Mutations of the Catalytic Subunit of Class IA PI3K Are Constitutively Active and Confer Factor-Independent Growth to Early Hematopoietic Cells.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1455-1455
Author(s):  
Stefan Horn ◽  
James McCubrey ◽  
Carol Stocking ◽  
Lorenz Truemper ◽  
Jorg Basecke
Keyword(s):  
Hot Spot ◽  
Hematopoietic Cells ◽  
Specific Inhibitor ◽  
Kinase Domain ◽  
Catalytic Subunit ◽  
Dependent Manner ◽  
Acute Leukemias ◽  
Activating Mutations ◽  
Exon 9

Abstract Background: Activating mutations of the catalytic subunit of class IA phosphoinositide 3-kinase alpha (PIK3CA) are clustered in small hot-spot regions of the PIK3CA gene, including exon 9 within the helical domain and exon 11 within the kinase domain. They have been linked to several human neoplasias, including colorectal, breast and hepatocellular cancers. In acute leukemias, PIK3CA mutations have not been investigated in larger chorts and so far only been observed in a few patients. Since the PI3K/Akt/GSK3beta pathway is an important signaling cascade of receptor tyrosine kinases (e.g. Flt3R, Kit) which are frequently activated in acute leukemias we investigated the functional activity of PIK3CA mutants. Materials and methods: We transfected early hematopoietic cells (Ba/F3 cell line) with PI3KCA exon 9 and 11 mutations and investigated the cells in an in vitro factor-independent growth assay and pharmacologic inhibition experiments. Results: We demonstrate that mutations in the helical or kinase domain of PIK3CA lead to the constitutive activation of PI3Kalpha in Ba/F3 cells, inducing factor-independent growth of the IL3-dependent cells. The frequency of IL3-independent Ba/F3 cells after tranfection with exon 9 and 11 PIK3CA mutants was equivalent to the frequency confered by PIK3CA mutants containing the membrane localization signal of either src or ras. Proliferation and survival of the cells were inhibited by the PI3K inhibitors LY294002 and Quercitin or an inhibitor of the PI3K downstream target Akt. Inhibition occurred in a dose- and time-dependent manner and could be reverted by addition of IL-3. One of the major targets of PI3K/Akt signaling is GSK3beta which becomes inactivated after Akt-mediated phosphorylation. By using a GSK3beta-specific inhibitor or LiCl we could show that the inactivation of GSK3beta alone did not result in factor-independent growth of Ba/F3 cells. However, GSK3beta inhibition led to a delay in the induction of cell death after IL3-withdrawal. Conclusion: Activating mutations of PIK3CA, associated with several human neoplasias and acute leukemia are functionally active in hematopoietic cells, confer factor independency and respond to PI3K/Akt inhibition.

Roscovitine, a specific inhibitor of cyclin-dependent protein kinases, reversibly inhibits chromatin condensation during in vitro maturation of porcine oocytes

Zygote ◽  
2001 ◽  
Vol 9 (4) ◽  
pp. 309-316 ◽  
Author(s):  
Carsten Krischek ◽  
Burkhard Meinecke
Keyword(s):  
Map Kinase ◽  
Protein Kinases ◽  
Chromatin Condensation ◽  
Specific Inhibitor ◽  
Histone H1 ◽  
Dependent Manner ◽  
Free Medium ◽  
Concentration Dependent Manner ◽  
Dependent Protein

In the present study the effects of roscovitine on the in vitro nuclear maturation of porcine oocytes were investigated. Roscovitine, a specific inhibitor of cyclin-dependent protein kinases, prevented chromatin condensation in a concentration-dependent manner. This inhibition was reversible and was accompanied by non-activation of p34cdc2/histone H1 kinase. It also decreased enzyme activity of MAP kinase, suggesting a correlation between histone H1 kinase activation and the onset of chromatin condensation. The addition of roscovitine (50 μM) to extracts of metaphase II oocytes revealed that the MAP kinase activity was not directly affected by roscovitine, which indicates a possible link between histone H1 and MAP kinase. Chromatin condensation occurred between 20 and 28 h of culture of cumulus-oocyte complexes (COCs) in inhibitor-free medium (germinal vesicle stage I, GV1: 74.6% and 13.7%, respectively). Nearly the same proportion of chromatin condensation was detected in COCs incubated initially in inhibitor-free medium for 20-28 h and subsequently in roscovitine-supplemented medium (50 μM) for a further 2-10 h (GV I: 76.2% and 18.8%, respectively). This observation indicates that roscovitine prevents chromatin condensation even after an initial inhibitor-free cultivation for 20 h. Extending this initial incubation period to ≥22 h led to an activation of histone H1 and MAP kinase and increasing proportions of oocytes exhibiting chromatin condensation in the presence of roscovitine. It is concluded that histone H1 kinase is involved in the induction of chromatin condensation during in vitro maturation of porcine oocytes.

scholarly journals An Intramolecular Association between Two Domains of the Protein Kinase Fused Is Necessary for Hedgehog Signaling

2004 ◽  
Vol 24 (23) ◽  
pp. 10397-10405 ◽  
Author(s):  
Manuel Ascano ◽  
David J. Robbins
Keyword(s):  
Signal Transduction ◽  
Protein Kinase ◽  
Hedgehog Signaling ◽  
Membrane Vesicles ◽  
Kinase Domain ◽  
Kinase Assay ◽  
Dependent Manner ◽  
Intramolecular Association

ABSTRACT The protein kinase Fused (Fu) is an integral member of the Hedgehog (Hh) signaling pathway. Although genetic studies demonstrate that Fu is required for the regulation of the Hh pathway, the mechanistic role that it plays remains largely unknown. Given our difficulty in developing an in vitro kinase assay for Fu, we reasoned that the catalytic activity of Fu might be highly regulated. Several mechanisms are known to regulate protein kinases, including self-association in either an intra- or an intermolecular fashion. Here, we provide evidence that Hh regulates Fu through intramolecular association between its kinase domain (ΔFu) and its carboxyl-terminal domain (Fu-tail). We show that ΔFu and Fu-tail can interact in trans, with or without the kinesin-related protein Costal 2 (Cos2). However, since the majority of Fu is found associated with Cos2 in vivo, we hypothesized that Fu-tail, which binds Cos2 directly, would be able to tether ΔFu to Cos2. We demonstrate that ΔFu colocalizes with Cos2 in the presence of Fu-tail and that this colocalization occurs on a subset of membrane vesicles previously characterized to be important for Hh signal transduction. Additionally, expression of Fu-tail in fu mutant flies that normally express only the kinase domain rescues the fu wing phenotype. Therefore, reestablishing the association between these two domains of Fu in trans is sufficient to restore Hh signal transduction in vivo. In such a manner we validate our hypothesis, demonstrating that Fu self-associates and is functional in an Hh-dependent manner. Our results here enhance our understanding of one of the least characterized, yet critical, components of Hh signal transduction.

scholarly journals Critical role for Epac1 in inflammatory pain controlled by GRK2-mediated phosphorylation of Epac1

2016 ◽  
Vol 113 (11) ◽  
pp. 3036-3041 ◽  
Author(s):  
Pooja Singhmar ◽  
XiaoJiao Huo ◽  
Niels Eijkelkamp ◽  
Susana Rojo Berciano ◽  
Faiza Baameur ◽  
...  
Keyword(s):  
Chronic Pain ◽  
Molecular Mechanism ◽  
Inflammatory Pain ◽  
Critical Role ◽  
Specific Inhibitor ◽  
Mechanical Hyperalgesia ◽  
Dependent Manner ◽  
Phosphorylation Event

cAMP signaling plays a key role in regulating pain sensitivity. Here, we uncover a previously unidentified molecular mechanism in which direct phosphorylation of the exchange protein directly activated by cAMP 1 (EPAC1) by G protein kinase 2 (GRK2) suppresses Epac1-to-Rap1 signaling, thereby inhibiting persistent inflammatory pain. Epac1−/− mice are protected against inflammatory hyperalgesia in the complete Freund’s adjuvant (CFA) model. Moreover, the Epac-specific inhibitor ESI-09 inhibits established CFA-induced mechanical hyperalgesia without affecting normal mechanical sensitivity. At the mechanistic level, CFA increased activity of the Epac target Rap1 in dorsal root ganglia of WT, but not of Epac1−/−, mice. Using sensory neuron-specific overexpression of GRK2 or its kinase-dead mutant in vivo, we demonstrate that GRK2 inhibits CFA-induced hyperalgesia in a kinase activity-dependent manner. In vitro, GRK2 inhibits Epac1-to-Rap1 signaling by phosphorylation of Epac1 at Ser-108 in the Disheveled/Egl-10/pleckstrin domain. This phosphorylation event inhibits agonist-induced translocation of Epac1 to the plasma membrane, thereby reducing Rap1 activation. Finally, we show that GRK2 inhibits Epac1-mediated sensitization of the mechanosensor Piezo2 and that Piezo2 contributes to inflammatory mechanical hyperalgesia. Collectively, these findings identify a key role of Epac1 in chronic inflammatory pain and a molecular mechanism for controlling Epac1 activity and chronic pain through phosphorylation of Epac1 at Ser-108. Importantly, using the Epac inhibitor ESI-09, we validate Epac1 as a potential therapeutic target for chronic pain.

scholarly journals Involvement of Cyclic Adenosine 3′,5′-Monophosphate in the Differential Regulation of Activin βA and βB Expression by Gonadotropin in the Zebrafish Ovarian Follicle Cells

Endocrinology ◽  
2003 ◽  
Vol 144 (2) ◽  
pp. 491-499 ◽  
Author(s):  
Yajun Wang ◽  
Wei Ge
Keyword(s):  
Oocyte Maturation ◽  
Ovarian Follicle ◽  
Mrna Level ◽  
Specific Inhibitor ◽  
Inhibitory Effect ◽  
Differential Regulation ◽  
Follicle Cells ◽  
Intracellular Camp ◽  
Dependent Manner

Activin is a dimeric protein consisting of two similar but distinct β-subunits, βA and βB. In our previous studies, both activin A (βAβA) and activin B (βBβB) have been demonstrated to stimulate oocyte maturation and promote oocyte maturational competence in the zebrafish. Follistatin, a specific activin-binding protein, can block both activin- and gonadotropin-induced final oocyte maturation in vitro, suggesting that activin is likely a downstream mediator of gonadotropin actions in the zebrafish ovary. In the present study, a full-length cDNA encoding zebrafish ovarian activin βA was cloned and sequenced. The precursor of zebrafish activin βA consists of 395 amino acids and its mature region exhibits about 78% homology with that of mammals. Using an in vitro primary culture of the ovarian follicle cells and semiquantitative RT-PCR assays, we examined the regulation of activin βA and βB expression by human chorionic gonadotropin (hCG) and its intracellular signal transduction mechanisms. hCG (15 IU/ml) increased the mRNA level of activin βA-subunit; however, it significantly down-regulated the steady-state expression level of activin βB in a time- and dose-dependent manner. The differential regulation of the two β-subunits by hCG could be mimicked by 3-isobutyl-1-methylxanthine, forskolin, and dibutyryl-cAMP, suggesting involvement of the intracellular cAMP pathway. Interestingly, H89 (a specific inhibitor of protein kinase A, PKA) could effectively block hCG- and forskolin-stimulated activin βA expression at 10 μm, but it was unable to reverse the inhibitory effects of hCG and forskolin on βB expression. This suggests that the hCG-stimulated activin βA expression is dependent on the activation of the cAMP-PKA pathway, whereas the inhibitory effect of hCG on activin βB expression is likely mediated by PKA-independent pathway(s).

scholarly journals β-Chemokines Enhance Parasite Uptake and Promote Nitric Oxide-Dependent Microbiostatic Activity in Murine Inflammatory Macrophages Infected with Trypanosoma cruzi

1999 ◽  
Vol 67 (9) ◽  
pp. 4819-4826 ◽  
Author(s):  
Júlio C. S. Aliberti ◽  
Fabiana S. Machado ◽  
Janeusa T. Souto ◽  
Ana P. Campanelli ◽  
Mauro M. Teixeira ◽  
...  
Keyword(s):  
Trypanosoma Cruzi ◽  
Neutralizing Antibodies ◽  
Specific Inhibitor ◽  
No Production ◽  
Dependent Manner ◽  
Macrophage Infection ◽  
Parasite Replication ◽  
Ifn Γ

ABSTRACT In the present study, we describe the ability of Trypanosoma cruzi trypomastigotes to stimulate the synthesis of β-chemokines by macrophages. In vivo infection with T. cruzi led to MIP-1α, RANTES, and JE/MCP1 mRNA expression by cells from peritoneal inflammatory exudate. In addition, in vitro infection with T. cruzi resulted in expression of β-chemokine MIP-1α, MIP-1β, RANTES, and JE mRNA by macrophages. The expression of the β-chemokine MIP-1α, MIP-1β, RANTES, and JE proteins by murine macrophages cultured with trypomastigote forms ofT. cruzi was confirmed by immunocytochemistry. Interestingly, macrophage infection with T. cruzi also resulted in NO production, which we found to be mediated mainly by β-chemokines. Hence, treatment with anti-β-chemokine-specific neutralizing antibodies partially inhibited NO release by macrophages incubated with T. cruzi parasites. Further, the addition of the exogenous β-chemokines MIP-1α, MIP-1β, RANTES, and JE/MCP-1 induced an increased T. cruzi uptake, leading to enhanced NO production and control of parasite replication in a dose-dependent manner. l-NMMA, a specific inhibitor of thel-arginine–NO pathway, caused a decrease in NO production and parasite killing when added to cultures of macrophages stimulated with β-chemokines. Among the β-chemokines tested, JE was more potent in inhibiting parasite growth, although it was much less efficient than gamma interferon (IFN-γ). Nevertheless, JE potentiates parasite killing by macrophages incubated with low doses of IFN-γ. Together, these results suggest that in addition to their chemotactic activity, murine β-chemokines may also contribute to enhancing parasite uptake and promoting control of parasite replication in macrophages and may play a role in resistance to T. cruziinfection.

scholarly journals Streptococcus gallolyticus Increases Expression and Activity of Aryl Hydrocarbon Receptor-Dependent CYP1 Biotransformation Capacity in Colorectal Epithelial Cells

2021 ◽  
Vol 11 ◽  
Author(s):  
Rahwa Taddese ◽  
Rian Roelofs ◽  
Derk Draper ◽  
Xinqun Wu ◽  
Shaoguang Wu ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Aryl Hydrocarbon Receptor ◽  
Specific Inhibitor ◽  
Intestinal Bacteria ◽  
Opportunistic Pathogen ◽  
Dependent Manner ◽  
Aryl Hydrocarbon ◽  
Streptococcus Gallolyticus

ObjectiveThe opportunistic pathogen Streptococcus gallolyticus is one of the few intestinal bacteria that has been consistently linked to colorectal cancer (CRC). This study aimed to identify novel S. gallolyticus-induced pathways in colon epithelial cells that could further explain how S. gallolyticus contributes to CRC development.Design and ResultsTranscription profiling of in vitro cultured CRC cells that were exposed to S. gallolyticus revealed the specific induction of oxidoreductase pathways. Most prominently, CYP1A and ALDH1 genes that encode phase I biotransformation enzymes were responsible for the detoxification or bio-activation of toxic compounds. A common feature is that these enzymes are induced through the Aryl hydrocarbon receptor (AhR). Using the specific inhibitor CH223191, we showed that the induction of CYP1A was dependent on the AhR both in vitro using multiple CRC cell lines as in vivo using wild-type C57bl6 mice colonized with S. gallolyticus. Furthermore, we showed that CYP1 could also be induced by other intestinal bacteria and that a yet unidentified diffusible factor from the S. galloltyicus secretome (SGS) induces CYP1A enzyme activity in an AhR-dependent manner. Importantly, priming CRC cells with SGS increased the DNA damaging effect of the polycyclic aromatic hydrocarbon 3-methylcholanthrene.ConclusionThis study shows that gut bacteria have the potential to modulate the expression of biotransformation pathways in colonic epithelial cells in an AhR-dependent manner. This offers a novel theory on the contribution of intestinal bacteria to the etiology of CRC by modifying the capacity of intestinal epithelial or (pre-)cancerous cells to (de)toxify dietary components, which could alter intestinal susceptibility to DNA damaging events.

scholarly journals Involvement of the vacuolar proton-translocating ATPase in multiple steps of the endo-lysosomal system and in the contractile vacuole system of Dictyostelium discoideum

1996 ◽  
Vol 109 (6) ◽  
pp. 1479-1495 ◽  
Author(s):  
L.A. Temesvari ◽  
J.M. Rodriguez-Paris ◽  
J.M. Bush ◽  
L. Zhang ◽  
J.A. Cardelli
Keyword(s):  
Morphological Changes ◽  
Specific Inhibitor ◽  
Fluid Phase ◽  
Contractile Vacuole ◽  
Dependent Manner ◽  
Concanamycin A ◽  
Latex Beads ◽  
And Function

We have investigated the effects of Concanamycin A (CMA), a specific inhibitor of vacuolar type H(+)-ATPases, on acidification and function of the endo-lysosomal and contractile vacuole (CV) systems of D. discoideum. This drug inhibited acidification and increased the pH of endo-lysosomal vesicles both in vivo and in vitro in a dose dependent manner. Treatment also inhibited endocytosis and exocytosis of fluid phase, and phagocytosis of latex beads. This report also confirms our previous conclusions (Cardelli et al. (1989) J. Biol. Chem. 264, 3454–3463) that maintenance of acidic pH in lumenal compartments is required for efficient processing and targeting of a lysosomal enzyme, alpha-mannosidase. CMA treatment compromised the function of the contractile vacuole complex as amoebae exposed to a hypo-osmotic environment in the presence of CMA, swelled rapidly and ruptured. Fluorescence microscopy revealed that CMA treatment induced gross morphological changes in D. discoideum cells, characterized by the formation of large intracellular vacuoles containing fluid phase. The reticular membranes of the CV system were also no longer as apparent in drug treated cells. Finally, this is the first report describing cells that can adapt in the presence of CMA; in nutrient medium, D. discoideum overcame the effects of CMA after one hour of drug treatment even in the absence of protein synthesis. Upon adaptation to CMA, normal sized endo-lysosomal vesicles reappeared, endo-lysosomal pH decreased, and the rate of endocytosis, exocytosis and phagocytosis returned to normal. This study demonstrates that the V-H(+)-ATPase plays an important role in maintaining the integrity and function of the endo-lysosomal and CV systems and that D. discoideum can compensate for the loss of a functional V-H(+)-ATPase.

Identification and Characterization of a Novel Jak2 Tyrosine Kinase Inhibitor.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3604-3604 ◽  
Author(s):  
Jacqueline Sayyah ◽  
David Ostrov ◽  
Peter Sayeski
Keyword(s):  
Growth Hormone ◽  
Tyrosine Kinase ◽  
In Silico ◽  
Jak2 V617f ◽  
Myeloproliferative Disorders ◽  
Kinase Domain ◽  
Dependent Manner ◽  
Dose Dependent ◽  
Tyrosine Autophosphorylation

Abstract Jak2 is a cytoplasmic tyrosine kinase that has been linked to hematological malignancies. Recently, a somatic Jak2 mutation (Jak2-V617F) has been identified in several myeloproliferative disorders such as polycythemia vera, essential thrombocythemia and myeloid metaplasia with myelofibrosis. These myeloproliferative disorders are characterized by unregulated expansion of one or more cells in the blood. The presence of the Jak2-V617F mutation in cells results in uncontrolled cell division and resistance to the negative feedback mechanisms that govern normal cell growth. The availability of a Jak2 tyrosine kinase specific inhibitor would facilitate our understanding of these Jak2-related disorders and perhaps serve a clinical benefit for patients. However, the most widely used Jak2 inhibitor, AG490, suffers from a general lack of specificity. Here, we used a novel approach to identify Jak2-specific inhibitors. We used in silico homology modeling of the Jak2 kinase domain to identify solvent accessible exposed pockets on the surface of the Jak2 protein. We then used a high-throughput program called DOCK to predict the ability of 20,000 small molecules to interact with a structural pocket adjacent to the ATP binding site of murine Jak2. The predicted binding energies of interaction between each compound and the Jak2 kinase domain were calculated and the top six scoring compounds were tested for their ability to inhibit Jak2 tyrosine kinase function in vitro. One of these compounds, 2-methyl-1-phenyl-4-pyridin-2-yl-2-(2-pyridin-2-ylethyl)butan-1-one (Z3) effectively inhibited Jak2-V617F and Jak2-WT autophosphorylation. We were able to show that Z3 inhibits total Jak2 tyrosine phosphorylation as well as Jak2 phosphorylation at the critical tyrosine 1007 residue in both a dose-and time-dependent manner. Z3 is able to reduce growth hormone-dependent Jak2 activation and is a direct inhibitor of Jak2-WT and Jak2-V617F tyrosine kinase autophosphorylation as measured by an in vitro kinase assay. Moreover, we found that Z3 inhibits proliferation of human erythroleukemia (HEL) cells, which express the Jak2-V617F mutation. In summary, this work demonstrates proof-of-principle concept that in silico molecular modeling can be used as a means to identify specific tyrosine kinase inhibitors. Z3 Inhibits Jak2 Tyrosine Autophosphorylation in a Dose-Dependent Manner Z3 Inhibits Jak2 Tyrosine Autophosphorylation in a Dose-Dependent Manner Z3 Inhibits Growth Hormone Mediated Jak2 Phosphorylation at Tyrosine 1007 Z3 Inhibits Growth Hormone Mediated Jak2 Phosphorylation at Tyrosine 1007

A Novel Method of Mobilizing Leukemia Initiating Cells by a Small Molecule Cdc42 Activity-Specific Inhibitor (CASIN) for Acute Myeloid Leukemia Therapy.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 13-13 ◽  
Author(s):  
Wei Liu ◽  
Benjamin Mizukawa ◽  
Mark Wunderlich ◽  
James F Johnson ◽  
James C. Mulloy ◽  
...  
Keyword(s):  
Small Molecule ◽  
Actin Polymerization ◽  
Specific Inhibitor ◽  
Conditional Knockout ◽  
Dependent Manner ◽  
Conventional Chemotherapy ◽  
Hematopoietic Stem ◽  
Bm Niche ◽  
Dose Dependent

Abstract Abstract 13 A large body of studies has proposed that leukemia initiating cells (LICs) are the culprit of leukemia relapse from conventional therapies. Like normal hematopoietic stem/progenitor cells (HSPCs), LICs are thought to reside in the bone marrow (BM) endothelial and/or endosteal niche. Although the full nature of LIC-niche interaction remains elusive, it has been postulated as a useful target for leukemia therapy based on a dual rationale: on one hand, the survival of LICs may depend upon interactions with specific niche, while on the other hand, chasing LICs out of the BM niche may drive quiescent LICs into active cell cycle, sensitizing them for conventional chemotherapy. Recent progresses in studying the PML tumor suppressor and the CXCR4-antagonist AMD3100 have provided strong support for such a rationale (Blood 113, 6215; Nature 453, 1072). The Rho GTPase family member Cdc42 is a central regulator of cell proliferation, adhesion, and migration by integrating signals from multiple cell surface receptors. Ablation of Cdc42 in HSPCs in a conditional knockout mouse model leads to massive egress of HSPCs from BM to the peripheral blood (PB), a phenotype attributable to deficiencies in HSPC adhesion, migration, and F-actin polymerization. We recently demonstrated that pharmacological targeting of Cdc42 by a small molecule Cdc42 activity-specific inhibitor (CASIN) transiently and specifically inhibits Cdc42 activity and mimics the Cdc42 knockout mobilization phenotype by suppressing HSPC adhesion, migration, and F-actin polymerization. CASIN appears to be active in this regard on both murine and human blood progenitors in vitro and in xenografted mice (Blood 112: 68a, Nature Biotechnology under revision). In the present studies, we hypothesize that pharmacological targeting of Cdc42 by CASIN is effective in mobilizing LICs from the BM niche, thus providing a new method for combinatory therapy against LICs. To test this hypothesis, we used MLL-AF9/N-Ras human AML cells (MA9/N-Ras), whereby the N-Ras G12D oncogene was introduced into MLL-AF9 transduced human CD34+ umbilical cord blood (HCB) cells. These cells grow vigorously in vitro independent of cytokine supplementation and induce AML readily in humanized NOD/SCID-SGM3 (SGM3) mice. Xenotransplant experiments confirmed that MA9/N-Ras cells are clonal inducers of leukemia with the property of LICs, as animals transplanted with either bulk cultures or with single cell derived cultures succumbed to AML with similar latencies. In MA9/N-Ras cells CASIN effectively inhibited downstream effectors of Cdc42 such as p-PAK, p-MLC and p-FAK in a dose-dependent manner. In the SGM3 mouse xenograft, we found CASIN administration (1.2 mg/kg, IV) transiently elicited mobilization of LICs from BM to PB by 20 minutes post injection. This was correlated with in vitro suppression of SDF-1α induced F-actin polymerization detected by FACS analysis and directional migration detected by a transwell assay upon CASIN treatment of the LICs (5-10 μM). Similar observations were made using Cdc42-specific shRNA knockdown of endogenous Cdc42 in the LICs. Continuous CASIN infusion into the xenografted mice for 5 days (1.2 mg/kg, IV, once daily) led to a potent induction of apoptosis of LICs detected by AnnexinV/7AAD staining. Significantly, the CASIN infusion showed no effects on the survival of HCB cells in xenografted SGM3 mice. In addition to a potential niche-dependent survival mechanism, the LICs, not normal HCB cells, appear to directly depend on Cdc42 for survival signals as further in vitro culture studies found that a 24-hour CASIN treatment resulted in a dose-dependent apoptosis of MA9/N-Ras cells, but not of normal HCBs. Finally, mouse genetic studies using MA9 transduced Mx-cre;Cdc42lox/lox BM cells transplanted into congenic BoyJ recipients showed that none of the mice with deleted Cdc42 upon pIpC injection developed AML while all mock-injected mice die from leukemia with less than 4 weeks latency, providing genetic evidence that Cdc42 is required for MA9-induced initiation of AML. Whether CASIN is effective in sensitizing the LICs to conventional chemotherapy in a combinatory regiment is currently under investigation. Our studies present a novel concept that pharmacological targeting of the intracellular signal transducer Cdc42 may have therapeutic value in eradicating LICs. Disclosures: No relevant conflicts of interest to declare.

scholarly journals The DNA-Dependent Protein Kinase Catalytic Subunit Is Phosphorylated In Vivo on Threonine 3950, a Highly Conserved Amino Acid in the Protein Kinase Domain

2006 ◽  
Vol 27 (5) ◽  
pp. 1581-1591 ◽  
Author(s):  
Pauline Douglas ◽  
Xiaoping Cui ◽  
Wesley D. Block ◽  
Yaping Yu ◽  
Shikha Gupta ◽  
...  
Keyword(s):  
Amino Acid ◽  
Protein Kinase ◽  
Kinase Domain ◽  
Catalytic Subunit ◽  
Protein Kinase Activity ◽  
Dependent Protein Kinase ◽  
Protein Kinase Domain ◽  
Dependent Protein

ABSTRACT The protein kinase activity of the DNA-dependent protein kinase (DNA-PK) is required for the repair of DNA double-strand breaks (DSBs) via the process of nonhomologous end joining (NHEJ). However, to date, the only target shown to be functionally relevant for the enzymatic role of DNA-PK in NHEJ is the large catalytic subunit DNA-PKcs itself. In vitro, autophosphorylation of DNA-PKcs induces kinase inactivation and dissociation of DNA-PKcs from the DNA end-binding component Ku70/Ku80. Phosphorylation within the two previously identified clusters of phosphorylation sites does not mediate inactivation of the assembled complex and only partially regulates kinase disassembly, suggesting that additional autophosphorylation sites may be important for DNA-PK function. Here, we show that DNA-PKcs contains a highly conserved amino acid (threonine 3950) in a region similar to the activation loop or t-loop found in the protein kinase domain of members of the typical eukaryotic protein kinase family. We demonstrate that threonine 3950 is an in vitro autophosphorylation site and that this residue, as well as other previously identified sites in the ABCDE cluster, is phosphorylated in vivo in irradiated cells. Moreover, we show that mutation of threonine 3950 to the phosphomimic aspartic acid abrogates V(D)J recombination and leads to radiation sensitivity. Together, these data suggest that threonine 3950 is a functionally important, DNA damage-inducible phosphorylation site and that phosphorylation of this site regulates the activity of DNA-PKcs.

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