Elevated telomerase activity and minimal telomere loss in cord blood long-term cultures with extensive stem cell replication

Blood ◽  
2004 ◽  
Vol 103 (12) ◽  
pp. 4440-4448 ◽  
Author(s):  
Loretta Gammaitoni ◽  
Katja C. Weisel ◽  
Monica Gunetti ◽  
Kai-Da Wu ◽  
Stefania Bruno ◽  
...  
Keyword(s):  
Stem Cell ◽  
Cord Blood ◽  
Telomere Length ◽  
Severe Combined Immunodeficiency ◽  
Telomerase Activity ◽  
Clinical Value ◽  
Telomere Shortening ◽  
Cd34 Cells

Abstract Telomerase activity, telomere length, stem/progenitor cell production, and function of CD34+ cells from cord blood (CB), bone marrow, and mobilized peripheral blood were evaluated in long-term cultures. CB cells were cultured either on OP-9 stromal cells transduced with an adenovector expressing thrombopoietin (TPO) or stimulated by a cytokine cocktail in the absence of stroma, with, in one method, CD34+ cells reisolated at monthly intervals for passage. Continuous expansion of stem cells as measured by in vitro cobblestone area and secondary colony-forming assays was noted for 18 to 20 weeks and by severe combined immunodeficiency (SCID)-repopulating cells (SRCs), capable of repopulating and serially passage in nonobese diabetic/SCID mice, for 16 weeks. Despite this extensive proliferation, telomere length initially increased and only at late stages of culture was evidence of telomere shortening noted. This telomere stabilization correlated with maintenance of high levels of telomerase activity in the CD34+ cell population for prolonged periods of culture. Cytokine-stimulated cultures of adult CD34+ cells showed CD34+ and SRC expansion (6-fold) for only 3 to 4 weeks with telomere shortening and low levels of telomerase. There is clearly a clinical value for a system that provides extensive stem cell expansion without concomitant telomere erosion. (Blood. 2004;103:4440-4448)

scholarly journals Imetelstat Inhibits Telomerase and Prevents Propagation of ADAR1-Activated Myeloproliferative Neoplasm and Leukemia Stem Cells

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 18-18
Author(s):  
Wenxue Ma ◽  
Larissa Balaian ◽  
Phoebe Mondala ◽  
Yudou He ◽  
Cayla Mason ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Telomere Length ◽  
Mouse Models ◽  
Telomerase Activity ◽  
Rna Seq ◽  
Publicly Traded ◽  
Cd34 Cells

BACKGROUND Clonal stem cell derived myeloproliferative neoplasms (MPNs) have a propensity to evolve to acute myeloid leukemia (AML). Deregulation of the innate immune deaminase associated with RNA1 (ADAR1) has been linked to malignant progression and therapeutic resistance. Increased expression of the stem cell gene, human telomerase reverse transcriptase (hTERT), has also been linked with malignant transformation. However, the combinatorial role of ADAR1 and hTERT in the evolution of MPN stem cells to therapy resistant acute myeloid leukemia stem cells (LSCs) and the capacity of a telomerase inhibitor, imetelstat, to prevent survival and self-renewal of pre-LSC and LSC had not been established. Recent clinical trials show early signs of efficacy of imetelstat in treatment of myelofibrosis (MF). However, its role in selectively inhibiting pre-LSC transformation to self-renewing LSC has not been elucidated. Here we show that targeting telomerase activity prevents pre-LSC and LSC maintenance both in vitro and in vivo, suggesting telomerase inhibition as an effective strategy for preventing MPN progression. METHODS To quantify hTERT level and ADAR1 activity in the setting of normal HSPC and MPN stem cell evolution, whole genome sequencing (WGS) analysis was performed on 76 normal and MPN blood CD34+ cells and matching saliva samples. Results were compared with RNA-seq of 100 FACS purified young, aged, MPN and AML CD34+CD38- stem cells and CD34+CD38+ progenitor cells. Confocal fluorescence microscopic evaluation of stem cell ADAR1 and hTERT localization, telomere length by Flow-FISH and telomerase activity by TRAP assays, lentiviral ADAR1 overexpression and shRNA knockdown were performed. In vitro stromal co-cultures, and humanized immunocompromised mouse models were established to determine the impact of imetelstat (a oligonucleotide inhibitor of telomerase) on normal, MPN stem cell and LSC maintenance. RESULTS Combined hTERT overexpression, ADAR1 activation and a significant reduction in telomere length correlated with accelerated stem cell aging during MPN progression to AML. Increased ADAR1 mediated adenosine to inosine (A-to-I) transcript editing coincided with accelerated telomere shortening in high risk MPN stem cells. Moreover, lentiviral ADAR1 overexpression enhanced pre-LSC engraftment. Treatment with imetelstat reduced MPN stem cell and LSC propagation in stromal co-cultures as well as in humanized mouse models commensurate with reduced hTERT expression levels and telomerase activity and decreased ADAR1 editing activity. Specifically, stromal co-culture assays revealed that combined treatment with dasatinib at 1 nM, and imetelstat at 1 µM or 5 µM significantly inhibited survival and replating of blast crisis (BC) CML progenitors compared with aged bone marrow progenitors (p < 0.001, ANOVA). As a single agent, imetelstat (5 µM) inhibited survival and replating of pre-LSC derived from myelofibrosis compared with normal bone marrow progenitor samples (p < 0.001, ANOVA). In pre-LSC MPN NSG-SGM mouse models established from 4 different MF samples, a significant reduction in proliferation of human CD45+ cells (p < 0.01, t test) was observed in bone marrow and spleen, when compared with vehicle control. Treatment of humanized LSC mouse models, established with 5 different BC CML, with 30 mg/kg of imetelstat, 3 times a week for 4 weeks resulted in a significant reduction in proliferation of malignant progenitors and human CD45+ cells (p < 0.001, ANOVA). As measured by a Flow-FISH assay, abnormal telomere length was reversed by imetelstat treatment compared with mismatch control (p < 0.05, ANOVA). In addition, FACS analysis revealed a significant reduction in activated beta-catenin expression after imetelstat treatment of LSC engrafted mice compared with vehicle control (p < 0.01, ANOVA). Finally, RNA-seq analysis performed on human CD34+ cells from imetelstat treated LSC mouse models revealed a significant reduction in LSC harboring malignant ADAR1-mediated A-to-I editing at doses that spared normal hematopoietic stem cells. CONCLUSIONS Combined WGS and RNA-Seq analyses, lentiviral ADAR1 overexpression, stromal co-culture assays and humanized pre-LSC and LSC mouse model studies reveal that pre-LSC evolution into LSC coincides with both ADAR1 and hTERT activation, which can be prevented with imetelstat. Disclosures Rizo: Geron Corp: Current Employment, Current equity holder in publicly-traded company. Huang:Geron Corp: Current Employment, Current equity holder in publicly-traded company. Jamieson:Forty Seven Inc: Patents & Royalties; Bristol-Myers Squibb: Other.

Long-Term Coculture of Adult Human Healthy Donor CD34+ Cells Shows Elevation of Telomeres in a Subgroup of Donors Independent of Age, Stem Cell Function and Telomerase Activity.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1695-1695
Author(s):  
Katja C. Weisel ◽  
Kaida Wu ◽  
Lothar Kanz ◽  
Malcolm A.S. Moore
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Telomere Length ◽  
Healthy Donor ◽  
Progenitor Cell ◽  
Telomerase Activity ◽  
Suspension Cells ◽  
Telomere Shortening ◽  
Cd34 Cells

Abstract Long-term cytokine-supplemented or stromal cocultures of human CD34+ cells, particularly from cord blood (CB), show expansion of hematopoietic progenitors and stem cells. Ultimately, however cultures decline and terminally differentiate. Despite upregulation of telomerase activity in proliferating primitive hematopoietic cells, telomere shortening has generally been reported in long-term cultures of CB, bone marrow or G-CSF mobilized peripheral blood CD34+ cells. In earlier reports, we described a long-term culture of hematopoietic stem cells on a murine OP9 bone marrow stroma cell line transfected with an adenovector expressing thrombopoietin, which allowed an extensive proliferation and self-renewal of CB CD34+ cells for 4–5 months with sustained elevation of telomerase activity and without concomitant significant telomere shortening (Blood, 2004). Here, we evaluated adult healthy donor peripheral blood (PB) CD34+ cells in the same OP9/Tpo coculture system. To determine progenitor and stem cell production, standard CFC and 2ndry cobblestone area-forming cell assays (CAFC assayed at 5 weeks on MS5 stroma) were undertaken weekly with suspension cells. In addition telomere length was measured by telomere restriction fragment (TRF) assay, and telomerase activity by TRAP assay on input CD34+ cells, and weekly on culture suspension cells. Maximum total cell, CFC and CAFC production was seen in the first 4 weeks with up to 80-fold expansion in cell count, up to 4-fold expansion in CFC and up to 13-fold expansion in CAFC. Thereafter a continuous decrease in production of cells, CFC 2ndry CAFC was observed and cultures terminated at week 8. Mean telomere length of input PB CD34+ cells was 9,5 ± 0,5 kbp. After 4 weeks in culture, telomere length remained stable (9,6 ± 0,5 kbp). In 3/6 cultures terminated, cultures showed only a slightly decrease of telomere length compared to the input population (0,55 ± 0,1 kbp loss). However, in 2/6 cultures we could demonstrate an elevation of telomeres (+ 0,3 kbp) independent of a rapid loss of telomerase activity in all cultures during the culture period. Furthermore, the elevation of telomeres did not correlate with an enhanced stem/progenitor cell activity. These data confirm earlier results of granulocyte telomere change in myeloma patients following chemotherapy and tandem transplantation, where 154/193 patients showed an expected loss of telomeres during the treatment period, whereas 39/193 patients had an unexpected elevation of telomeres. We could now show in healthy donors that this phenomenon is independent of bone marrow stress due to chemotherapeutic treatment. In conclusion, we could show that the stromal coculture system with OP9/Tpo is highly effective in stem/progenitor cell expansion not only in CB but also in PB CD34+ cells. It is the first culture system, which allows expansion of hematpoietic cells without significant telomere erosion. We furthermore describe for the first time an age-independent healthy donor population which shows telomerase-independent, significant telomere elevation. Further studies have to demonstrate, if this phenomenon is potentially linked to a higher susceptibility for cancer disease.

scholarly journals High Integrity and Fidelity of Long-Term Cryopreserved Umbilical Cord Blood for Transplantation

2021 ◽  
Vol 10 (2) ◽  
pp. 293
Author(s):  
Gee-Hye Kim ◽  
Jihye Kwak ◽  
Sung Hee Kim ◽  
Hee Jung Kim ◽  
Hye Kyung Hong ◽  
...  
Keyword(s):  
Stem Cell ◽  
Cord Blood ◽  
Umbilical Cord ◽  
Umbilical Cord Blood ◽  
Clinical Applications ◽  
Hematopoietic Stem ◽  
Cd34 Cells ◽  
Hsc Transplantation

Umbilical cord blood (UCB) is used as a source of donor cells for hematopoietic stem cell (HSC) transplantation. The success of transplantation is dependent on the quality of cord blood (CB) units for maximizing the chance of engraftment. Improved outcomes following transplantation are associated with certain factors of cryopreserved CB units: total volume and total nucleated cell (TNC) count, mononuclear cell (MNC) count, and CD34+ cell count. The role of the storage period of CB units in determining the viability and counts of cells is less clear and is related to the quality of cryopreserved CB units. Herein, we demonstrate the recovery of viable TNCs and CD34+ cells, as well as the MNC viability in 20-year-old cryopreserved CB units in a CB bank (MEDIPOST Co., Ltd., Seongnam-si, Gyeonggi-do, Korea). In addition, cell populations in CB units were evaluated for future clinical applications. The stable recovery rate of the viability of cryopreserved CB that had been stored for up to 20 years suggested the possibility of uses of the long-term cryopreservation of CB units. Similar relationships were observed in the recovery of TNCs and CD34+ cells in units of cryopreserved and fresh CB. The high-viability recovery of long-term cryopreserved CB suggests that successful hematopoietic stem cell (HSC) transplantation and other clinical applications, which are suitable for treating incurable diseases, may be performed regardless of long-term storage.

Extensive Chromosome Instability in Acute Myeloid Leukemia Is Associated with Critical Telomere Shortening.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3376-3376
Author(s):  
Susan J.J. Swiggers ◽  
Marianne A. Kuijpers ◽  
Maartje J. de Cort ◽  
Berna Beverloo ◽  
J. Mark J.M. Zijlmans
Keyword(s):  
Telomere Length ◽  
Reciprocal Translocation ◽  
Genetic Instability ◽  
Myeloid Leukemia ◽  
Chromosomal Abnormalities ◽  
Chromosome Instability ◽  
Telomerase Activity ◽  
In Vitro Models ◽  
Telomere Shortening

Abstract Telomeres, the ends of linear chromosomes, have a critical role in protection against chromosome end-to-end fusion. Telomeres shorten in every cell division due to the end replication problem. Telomerase is a reverse transcriptase that adds telomeric DNA repeats to the ultimate chromosome end. In vitro models of long-term fibroblast cultures have identified two sequential mortality stages, senescence (M1) and crisis (M2). Senescence can be bypassed by loss of p53 or Rb function, whereas escape from crisis can only be achieved by activating a telomere maintenance mechanism, mostly telomerase reactivation. Cells that bypass senescence (M1) did not reactivate telomerase, resulting in further telomere shortening to a critical telomere length upon reaching crisis (M2). In these models, critical telomere shortening induces extensive chromosome instability, most likely via chromosome end-to-end fusions. Dicentric chromosomes lead to anaphase breakage-fusion-bridges resulting in multiple chromosomal aberrations. To investigate whether similar mechanisms may be involved in the development of genetic instability in human cancer, we studied telomere length and expression of critical telomeric proteins (TRF2 and POT1) in acute myeloid leukemia (AML) patients. AML is a good model for these studies since distinct subgroups of AML are characterized by either exchanges along chromosome arms (translocation or inversion), or by a complex karyotype with multiple chromosome aberrations. Groups were age-matched. Telomere length was studied in metaphase arrested leukemic cells using quantitative fluorescence in situ hybridization (Q-FISH) using a telomere-specific probe. Subsequently, metaphase spreads were hybridized with a leukemia-specific probe to confirm leukemic origin of each metaphase. Telomeres were significantly shorter in AML samples with multiple chromosomal abnormalities in comparison to AML samples with a reciprocal translocation/inversion or no abnormalities (mean±SEM=16±1.7 AFU, n=12 versus 29±4.3 AFU, n=18; p=0.015). Interestingly, telomerase activity level is significantly higher in AML samples with multiple chromosomal abnormalities, compared to AML samples with a reciprocal translocation or inversion (mean±SEM=330±95, n=11 versus 70±21, n=13; p=0.02). Expression levels of telomeric proteins TRF2 and POT1 were similar in these AML groups. Our observations suggest that, consistent with previous in vitro models in fibroblasts, critical telomere shortening may have a role in the development of genetic instability in human AML. Critically short telomeres in association with high levels of telomerase activity suggest that AML cells with multiple chromosomal abnormalities have bypassed crisis (M2). The longer telomeres and low levels of telomerase activity in AML cells with a reciprocal translocation or inversion suggest that they originate from an earlier stage, preceding crisis. Consequently, telomere length modulation may have a role in cancer prevention.

Ex-Vivo Generation and Expansion of Both Lymphoid and Myeloid Lineages from Human Cord Blood (CB) HSC Using a Serum-Free Human Mesenchymal Stem Cell Based Culture System.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2888-2888
Author(s):  
Ana Frias ◽  
Christopher D. Porada ◽  
Kirsten B. Crapnell ◽  
Joaquim M.S. Cabral ◽  
Esmail D. Zanjani ◽  
...  
Keyword(s):  
Stem Cell ◽  
Cord Blood ◽  
Culture System ◽  
Ex Vivo ◽  
Cell Number ◽  
Human Cord Blood ◽  
Serum Free ◽  
Gm Csf ◽  
Cd34 Cells

Abstract The in vitro culture of a hematopoietic stem cell (HSC) graft with either media containing animal-derived components or a feeder layer with ill-defined pathogenic potential such as xenogeneic cell lines or cells modified by viral transformation poses risks that concern scientists and regulatory agencies. In the present studies, we avoided these risks by evaluating the ability of a human stromal-based serum free culture system (hu-ST) to support the ex-vivo expansion/maintenance of human CB HSC. CB CD34+ enriched cells were cultured in serum free medium in the presence of hu-ST with SCF, bFGF, LIF and Flt-3, and the cultures were analyzed for expansion, phenotype and clonogenic ability. We have previously reported the ability of this culture system to allow the successful expansion/maintenance of HSC along the myeloid pathway. In the present study, we investigated whether we could further develop this culture system to simultaneously expand myelopoiesis and lymphopoiesis in vitro. To this end, cord blood CD34+ cells were cultured for a total of 28 days and analyzed every 3 days for expansion and phenotype. There was a progressive increase in CD34 cell number with time in culture. The differentiative profile was primarily shifted towards the myeloid lineage with the presence of CD33, CD15, and CD14. However, a significant number of CD7+ cells were also generated. At week 2 of culture, we observed that 30% of the cells in the culture were CD7 positive. These CD7+CD2-CD3-CD5-CD56-CD16-CD34- cells were then sorted and either plated on top of new irradiated hu-ST layers in the presence of SCF, FLT-3, IL-7, IL-2, and IL-15, or cultured with IL-4, GM-CSF, and FLT-3 in the absence of stroma. Both of these cultures were maintained for an additional 2 weeks. In both sets of cultures, further expansion in the total cell number occurred with the time in culture, and by the end of the week 2, we observed that 25.3±4.18% of the cells had become CD56+ CD3-, a phenotype consistent with that of NK cells. Furthermore, cytotoxicity assays were performed and showed cytotoxic activity that increased in an E:T ratio-dependent fashion. 38.6% of the CD7+ cells grown in the presence of IL-4, GM-CSF, and FLT-3 became CD123+CD11c-, a phenotype characteristic of nonactivated dendritic cells, while 7.3–12.1% adopted an activitated dendritic cell phenotype CD83+CD1a+. In summary, we developed an in vitro culture system that reproducibly allows the effective ex vivo expansion of human cord blood HSCs while maintaining the capability of generating both myeloid and lymphoid hematopoiesis in vitro.

Telomerase Activity and Telomere Length of CD4+CD25+ Regulatory T-Cells under Conditions of In Vitro and In Vivo Expansion.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3857-3857
Author(s):  
Dominik G.F. Wolf ◽  
Anna M. Wolf ◽  
Christian Koppelstaetter ◽  
Holger F. Rumpold ◽  
Gert Mayer ◽  
...  
Keyword(s):  
T Cells ◽  
Regulatory T Cells ◽  
Telomere Length ◽  
Cancer Patients ◽  
Telomerase Activity ◽  
Telomere Maintenance ◽  
Healthy Human ◽  
Telomere Shortening

Abstract The expandability of CD4+CD25+ regulatory T-cells (Treg) has been shown in vitro and in vivo. Activation of telomerase activity is a prerequisite for clonal expansion and telomere maintenance in T-cells. There is currently no data available on the expression and function of telomerase in proliferating Treg. Analyses of telomere length by flow-FISH, real-time PCR and Southern blotting revealed that Treg isolated from healthy human volunteers have significantly shortened telomeres when compared to CD4+CD25− T-cells. However, telomere length is not further shortened in Treg isolated from the peripheral blood of cancer patients, despite the observation that the regulatory T-cell pool of these patients was significantly enlarged. To gain further insight into maintenance of telomere length of Treg, we induced in vitro proliferation of Treg by stimulation with anti-CD3 and IL-2. This led to a rapid increase of telomerase activity, as determined by PCR-ELISA. However, when we focused on the proliferating fraction of Treg using a sorting strategy based on the dilution of CFSE, we could show a significant telomere shortening in Treg with high proliferative and immmuno-suppressive capacity. Of note, proliferating CFSElow Treg are characterized by high telomerase activity, which however seems to be insufficient to avoid further telomere shortening under conditions of strong in vitro stimulation. In contrast, under conditions of in vivo expansion of Treg in cancer patients, the induction of telomerase activity is likely to compensate for further telomere erosion. These data might be of importance when considering the application of in vitro expanded Treg for the treatment of GvHD or autoimmune diseases, as telomere shortening might be associated with genomic instability.

Maintenance of Telomere Length in Peripheral Blood CD4+CD25+ Regulatory T-Cells of Cancer Patients Despite Active Proliferation.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3309-3309
Author(s):  
Dominik Wolf ◽  
Holger Rumpold ◽  
Christian Koppelstaetter ◽  
Guenther Gastl ◽  
Eberhard Gunsilius ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Regulatory T Cells ◽  
Telomere Length ◽  
Cancer Patients ◽  
Peripheral Blood ◽  
Telomerase Activity ◽  
Telomere Shortening ◽  
Active Proliferation

Abstract CD4+CD25+ regulatory T-cells (Treg) are increased in the peripheral blood of cancer patients. It remains unclear whether this is due to redistribution or active proliferation. The latter would require the up-regulation of telomerase activity, whose regulation also remains unknown for Treg. We therefore isolated Treg and the respective CD4+CD25− control T-cell population from peripheral blood of cancer patients (n=23) and healthy age-matched controls (n=17). Analysis of their content of T-cell receptor excision circles (TREC) revealed that the observed increase of Treg frequencies in peripheral blood is due to active cycling rather than to redistribution from other compartments (i.e. secondary lymphoid organs or bone-marrow), as Treg from cancer patients are characterized by a significant decrease of TREC content when compared to TREC content of Treg isolated from healthy age-matched controls. Surprisingly, despite their proven in vivo proliferation, telomere length is not further shortened in Treg from peripheral blood of cancer patients as shown by Flow-Fish, Real-Time PCR and Southern Blotting. Accodingly, telomerase activity of Treg was readily inducible in vitro by OKT3 together with IL-2. Notably, sorting of in vitro proliferating Treg using dilution of CFSE revealed a significant telomere shortening in Treg with high proliferative capacity (i.e. CFSElow fraction) under conditions of strong in vitro stimulatory growth conditions despite a high telomerase activity. Thus, under conditions of strong in vitro stimulation induction of telomerase seems to be insufficient to avoid progressive telomere shortening. In contrast, in actively proliferating peripheral blood Treg from patients with epithelial malignancies induction of telomerase activity is likely to compensate for further telomere erosion.

The Polycomb Gene BMI1 Collaborates with BCR-ABL in Leukemic Transformation of Human Cord Blood CD34+ Cells.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1350-1350
Author(s):  
Aleksandra Rizo ◽  
Sandra Olthof ◽  
OS van Ronald ◽  
Bert HJ Dontje ◽  
Edo Vellenga ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Stem Cell ◽  
B Cells ◽  
Cord Blood ◽  
Bone Marrow Microenvironment ◽  
Leukemic Transformation ◽  
Human Cord Blood ◽  
Self Renewal ◽  
Cd34 Cells

Abstract Previously, we demonstrated that BMI1 acts as a stem cell maintenance factor for human stem/progenitor cells. Here, we report that BMI1 collaborates with BCR-ABL in inducing leukemogenic transformation of human cord blood (CB) CD34+ cells. BMI1 and BCR-ABL were co-expressed into CB CD34+ cells (further referred as B/B cells) using a retroviral approach and cells were transplanted into NOD-SCID mice. In two out of five mice we observed leukemia within 4 months after transplantation. Chimerism levels reached 80–90% in the bone marrow and peripheral blood and morphological analysis revealed the appearance of primitive blast-like human hematopoietic cells with features that recapitulate human lymphoid leukemia. The mice were lethargic, with splenomegaly and infiltration of leukemic cells in the spleen, liver and the bone marrow and immunophenotypical analyses revealed that the cells expressed CD34 and CD19. To further understand the mechanisms underlying the leukemic transformation we performed ex-vivo long-term cultures on bone marrow stroma. We observed that the double transduced B/B cells had a strong proliferative advantage and elevated self-renewal potential as compared to controls. Expanding cultures could be maintained for over 20 weeks and Cobblestone Area Forming Cells (CAFCs) could be harvested and replated to initiate new expanding cocultures. Stem cell frequencies were determined in Long-Term Culture-Initiating Cell (LTC-IC) assays and frequencies were enhanced over 100-fold as compared to controls. Depending on the MS5 co-culture conditions, both myeloid as well as lymphoid long-term cultures could be established, indicating that extrinsic factors might dictate the lineage fate of transformed cells. To determine the necessity of a bone marrow microenvironment, we performed stroma-free liquid cultures and observed that the B/B cells were capable of expanding over 23 weeks, BMI1 cells were able to grow for 16 weeks and, importantly, BCR-ABL cells were not able to propagate long-term in stromain-dependent cultures. Thus, these data suggest that BCR-ABL cells are still dependent on cues from the bone marrow microenvironment for long-term self-renewal, and that co-expression of the intrinsic stem cell regulator BMI1 might alleviate this necessity of BCR-ABL+ cells for a microenvironment. Experiments in which B/B-transduced cells were sorted into HSC, CMP, GMP and MEP populations indicated that long-term self-renewal and expansion could particularly be imposed on the HSC population, and much less efficiently on progenitor subpopulations. In order to study whether the B/B-leukemic stem cells could be targeted by Imatinib, we applied a short pulse of Imatinib to expanding MS5 cocultures for 7 days. While the vast majority of cells in all cultures did not survive, in the B/B-transduced group a population of immature cells remained that was capable of re-initiating proliferative cultures of self-renewing CAFCs with very high frequencies (1/96 as determined by LTC-IC assays). Finally, we asked whether retroviral introduction of BMI1 in BCR-ABL+ CD34+ cells isolated from CML patients in chronic phase that expressed low endogenous BMI1 levels would affect long-term growth and self-renewal. Upon overexpression of BMI1 we observed increased proliferation capacity of the BMI1 transduced CML cells, and cultures could be maintained for much longer periods than control-transduced cultures. In conclusion, our data indicate that BMI1 collaborates with BCR-ABL in leukemic transformation, and our human-based system should provide a useful model to study the pathology of leukemias and test new drug entities.

Functional p53 Is Required for Effective Telomerase Inhibition in BCRABL- Positive CML Cells in Vitro

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 572-572
Author(s):  
Ute Brassat ◽  
Stefan Balabanov ◽  
Melanie Braig ◽  
Daniel Bali ◽  
Kerstin Borgmann ◽  
...  
Keyword(s):  
Telomere Length ◽  
Growth Kinetics ◽  
Blast Crisis ◽  
Telomerase Activity ◽  
Gfp Expression ◽  
Telomere Shortening ◽  
Telomerase Inhibition ◽  
Group A ◽  
Group B

Abstract Telomeres consist of repeat structures such as (TTAGGG)n in vertebrates and are localized at the end of chromosomes. Replication-dependent telomere shortening due to the end-replication problem can be counteracted by upregulation of an endogenous reverse transcriptase called telomerase. Increasing evidence suggests that critical telomere shortening results in genetic instability which may promote tumour evolution and telomerase activation during which critically short telomeres are stabilised and ongoing tumour growth is facilitated. In Chronic myeloid leukemia (CML) the high turnover of the malignant clone is driven by the oncogene BCR-ABL and leads to accelerated telomere shortening in chronic phase (CP) compared to telomere length in healthy individuals. Telomere shortening has been demonstrated to be correlated with disease stage, duration, prognosis and response to molecular targeted treatment. Despite of the accelerated telomere shortening observed, telomerase activity is increased in CP CML and further upregulated with progression of the disease to accelerated phase or blast crisis (AP/BC). To investigate the effect of telomerase inhibition on BCR-ABL-positive cells, we expressed a dominant-negative mutant of hTERT (vector pOS DNhTERT-IRES-GFP) in K562 cells. The cells were single sorted and clones in addition to bulk cultures were long term expanded in vitro. The expression of the transgene DNhTERT was monitored by the expression of GFP and function of DNhTERT was analyzed by measurement of telomere length (by flow-FISH) and telomerase activity (TRAP assay). Evaluation of these parameters showed the following patterns of growth kinetics and telomere biology in individual clones: Two clones lost telomere repeats and were transiently delayed in growth kinetics but eventually escaped from crisis without loss of GFP expression (indicated by a re-increase in telomere length and growth rate, group A) Three other clones lost GFP expression after initial and significant telomere reduction indicating loss of the transgene (group B). Finally, telomere length and growth kinetics of two remaining clones and of the bulk culture cells remained unaffected by expression of DN-hTERT (group C). Of note, none of the clones analyzed either died or entered cell cycle arrest. Further analyses of one clone of group A revealed impaired DNA damage response indicated by two fold increase in number of γH2AX foci in comparison to control cells. Moreover, the expression pattern of genes involved in DNA repair was significantly altered (Dual chip®). Network analysis of the altered genes using MetaCore® software confirmed p53 as a key regulator in signaling of DNA damage in these cells. CML blast crisis cell lines such as K562 are typically negative for functional p53 and p16INK4. Therefore, we went on and investigate if the presence of functional p53 is required for the induction of telomere-mediated apoptosis or senescence in BCR-ABL-positive cells. For this purpose, we restored p53 in telomerase-negative clones by using an inducible system (vector pBABE p53ERtam) in two clones from group A and group B. Induction of p53 in cells with critically short telomeres (telomere length 4–5 kb) lead to immediate induction of apoptosis while vector control cells continued to escape from crisis. These results suggest that the success of strategies aimed at telomerase inhibition in CML is dependent on the presence of functional p53 in BCR-ABL-positive cells which argues in favour of applying these strategies preferentially in CP as opposed to BC.

scholarly journals Functional Diversification of Replication Protein A Paralogs and Telomere Length Maintenance in Arabidopsis

Genetics ◽  
2020 ◽  
Vol 215 (4) ◽  
pp. 989-1002
Author(s):  
Behailu B. Aklilu ◽  
François Peurois ◽  
Carole Saintomé ◽  
Kevin M. Culligan ◽  
Daniela Kobbe ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Telomere Length ◽  
Protein A ◽  
Replication Protein A ◽  
Telomerase Activity ◽  
Replication Protein ◽  
Telomeric Dna ◽  
Telomere Shortening ◽  
Replication Group

Replication protein A (RPA) is essential for many facets of DNA metabolism. The RPA gene family expanded in Arabidopsis thaliana with five phylogenetically distinct RPA1 subunits (RPA1A-E), two RPA2 (RPA2A and B), and two RPA3 (RPA3A and B). RPA1 paralogs exhibit partial redundancy and functional specialization in DNA replication (RPA1B and RPA1D), repair (RPA1C and RPA1E), and meiotic recombination (RPA1A and RPA1C). Here, we show that RPA subunits also differentially impact telomere length set point. Loss of RPA1 resets bulk telomeres at a shorter length, with a functional hierarchy for replication group over repair and meiosis group RPA1 subunits. Plants lacking RPA2A, but not RPA2B, harbor short telomeres similar to the replication group. Telomere shortening does not correlate with decreased telomerase activity or deprotection of chromosome ends in rpa mutants. However, in vitro assays show that RPA1B2A3B unfolds telomeric G-quadruplexes known to inhibit replications fork progression. We also found that ATR deficiency can partially rescue short telomeres in rpa2a mutants, although plants exhibit defects in growth and development. Unexpectedly, the telomere shortening phenotype of rpa2a mutants is completely abolished in plants lacking the RTEL1 helicase. RTEL1 has been implicated in a variety of nucleic acid transactions, including suppression of homologous recombination. Thus, the lack of telomere shortening in rpa2a mutants upon RTEL1 deletion suggests that telomere replication defects incurred by loss of RPA may be bypassed by homologous recombination. Taken together, these findings provide new insight into how RPA cooperates with replication and recombination machinery to sustain telomeric DNA.

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