3-Formylchromone Counteracts STAT3 Signaling Pathway by Elevating SHP-2 Expression in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading cancers that contribute to a large number of deaths throughout the globe. The signal transducer and activator of transcription 3 (STAT3) is a tumorigenic protein that is overactivated in several human malignancies including HCC. In the present report, the effect of 3-formylchromone (3FC) on the STAT3 signaling pathway in the HCC model was investigated. 3FC downregulated the constitutive phosphorylation of STAT3 and non-receptor tyrosine kinases such as JAK1 and JAK2. It also suppressed the transportation of STAT3 to the nucleus and reduced its DNA-binding ability. Pervanadate treatment overrode the 3FC-triggered STAT3 inhibition, and the profiling of cellular phosphatase expression revealed an increase in SHP-2 levels upon 3FC treatment. The siRNA-driven deletion of SHP-2 led to reinstate STAT3 activation. 3FC downmodulated the levels of various oncogenic proteins and decreased CXCL12-driven cell migration and invasion. Interestingly, 3FC did not exhibit any substantial toxicity, whereas it significantly regressed tumor growth in an orthotopic HCC mouse model and abrogated lung metastasis. Overall, 3FC can function as a potent agent that can display antitumor activity by targeting STAT3 signaling in HCC models.

Dynamic cell cycle-dependent phosphorylation modulates CENP-L-CENP-N centromere recruitment

The kinetochore is a macromolecular structure that is required to ensure proper chromosome segregation during each cell division. The kinetochore is assembled upon a platform of the 16-subunit Constitutive Centromere Associated Network (CCAN), which is present at centromeres throughout the cell cycle. The nature and regulation of CCAN assembly, interactions, and dynamics required to facilitate changing centromere properties and requirements remain to be fully elucidated. The CENP-LN CCAN sub-complex displays a unique cell cycle-dependent localization behavior, peaking in S phase. Here, we demonstrate that phosphorylation of CENP-L and CENP-N controls CENP-LN complex formation and localization in a cell cycle-dependent manner. Mimicking constitutive phosphorylation of either CENP-L or CENP-N or simultaneously preventing phosphorylation of both proteins prevents CENP-LN localization and disrupts chromosome segregation. Together, our work suggests that cycles of phosphorylation and dephosphorylation are critical for CENP-LN complex recruitment and dynamics at centromeres to enable cell cycle-dependent CCAN reorganization.

Leukemic Cells Expressing ETV6-Frk Identified in a Refractory B-ALL Patient Are Sensitive to Dasatinib in Vitro

[Background] ETV6-FRK is a rare kinase-related fusion gene which was identified only in acute myeloid leukemia (Hosoya N, et al. Genes Chromosomes Cancer. 2005). Herein, we firstly identified ETV6-FRK fusion gene in a patient with high-risk pediatric B cell precursor ALL (B-ALL). Because FRK is Src family tyrosine kinase, we performed functional analysis of ETV6-FRK to establish molecular targeting therapy. [Patient] A 11-year-old boy with B-ALL was refractory to conventional chemotherapy and received allogeneic bone marrow transplantation (allo-BMT) following two courses of blinatumomab. This patient maintains complete remission for three months after allo-BMT. Cytogenetic analysis demonstrated t(6;12)(q21;p13) as a part of complex karyotype. Targeted capture mRNA sequencing identified ETV6-FRK fusion transcript in this patient. [Materials and methods] ETV6-FRK fusion was validated by RT-PCR of the diagnostic leukemic sample from this patient. Full length of ETV6-FRK cDNA was cloned into retroviral vector with Tet-On system. Then, Ba/F3 cells, which are IL-3 dependent murine pro B-ALL cells, were transduced with retroviral vector to establish Ba/F3 cells expressing ETV6-FRK (Ba/F3-ETV6-FRK) under doxycycline (DOX) dependent manner. Ba/F3-ETV6-FRK was analyzed whether IL-3 independent growth was achieved. To determine whether aberrant activation of FRK-STAT pathway as the downstream effects of ETV6-FRK, activation of FRK-STAT pathway was evaluated by western blot. Finally, in cytotoxic assay, proliferation of Ba/F3-ETV6-FRK was assessed under the media with various concentrations of dasatinib, a tyrosine kinase inhibitor. [Results and discussions] Sequencing of RT-PCR product revealed that ETV6 exon 4 was fused in-frame to FRK exon 3, creating an ETV6-FRK fusion gene. The ETV6-FRK fusion gene produced a chimeric protein consisting of the entire pointed (PNT) oligomerization domain of ETV6 and the kinase domain of FRK (Fig 1). The expression of ETV6-FRK in Ba/F3 cells under DOX dependent manner was confirmed by western blot. Ba/F3-ETV6-FRK proliferated without IL-3 in contrast to Ba/F3 cells not expressing ETV6-FRK (p<0.01), suggesting ETV6-FRK had proliferation activity. Western blot analysis revealed constitutive phosphorylation of tyrosine residues of ETV6-FRK and STAT5/STAT3/STAT1, suggesting constitutive activation of FRK-STATs pathway was associated with IL-3 independent proliferation activity of ETV6-FRK. Considering that dasatinib, which is Src-kinase inhibitor, could block constitutive phosphorylation of ETV6-FRK, we hypothesized that dasatinib might block the IL-3 independent proliferation of Ba/F3-ETV6-FRK. In vitro killing assay showed that dasatinib suppressed efficiently the proliferation of Ba/F3-ETV6-FRK with 50% inhibitory concentration (IC50) 1.64 ± 0.02 nM, although dasatinib didn't show any effect on Ba/F3 cells not expressing ETV6-FRK (Fig. 2). Annexin V assay determined that 35.8 ± 6.9 % of Ba/F3-ETV6-FRK with dasatinib (10nM, 48hrs) were apoptotic than Ba/F3 cells not expressing ETV6-FRK (Fig. 3, p<0.01). These findings suggested that dasatinib abolished the proliferation activity of ETV6-FRK selectively. [Conclusion] We identified the first patient of pediatric high-risk B-ALL harboring ETV6-FRK fusion by targeted capture mRNA sequencing, who was refractory to the conventional chemotherapy. We also provide the first evidence that dasatinib could abrogate proliferation activity of ETV6-FRK in vitro, suggesting that dasatinib might be effective for the patient with B-ALL carrying a ETV6-FRK fusion. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

The role of HER2 and HER3 in HER2-amplified cancers beyond breast cancers

HER2 and HER3 play key driving functions in the pathophysiology of HER2-amplified breast cancers, but this function is less well characterized in other cancers driven by HER2 amplification. This study aimed to explore the role of HER2 and HER3 signaling in other types of HER2-amplified cancer. The expression and signaling activity of HER2, HER3, and downstream pathway proteins were studied in cell panels representing HER2-amplified cancers of the breast, bladder, colon and rectal, stomach, esophagus, lung, tongue, and endometrium along with controls lacking HER2 amplification. We report that HER2-amplified cancers are addicted to HER2 across different cancer types and the depth of addiction is best linked with the expression level of HER2, but not with HER3 expression. We report that the expression and constitutive phosphorylation of HER3 are ubiquitous in HER2-amplified breast cancer cell lines, but much more variable in HER2-amplified cancer cells from other tissues. We observed the lapatinib-induced compensatory upregulation of HER3 signaling in many types of HER2-amplified cancers, although with much variability. We find that HER3 expression is essential for in vivo tumorigenic growth in some HER2-amplified tumors but not others. Importantly HER3 expression level does not correlate well with its functional importance. More biomarkers will be needed to guide the optimal use of HER3 inhibitors in HER2-amplified cancers from non-breast origin. Unlike oncogenes activated through mutational events, the activation of HER2 through overexpression represents a gradient of activities and depth of addiction and the response to inhibitors follows a similar gradient.

IRE1 Alpha/XBP1 Axis Sustains Primary Effusion Lymphoma Cell Survival by Promoting Cytokine Release and STAT3 Activation

Primary Effusion Lymphoma (PEL) is a highly aggressive B cell lymphoma associated with Kaposi’s Sarcoma-associated Herpesvirus (KSHV). It is characterized by a high level of basal Endoplasmic Reticulum (ER) stress, Unfolded Protein Response (UPR) activation and constitutive phosphorylation of oncogenic pathways such as the Signal Transducer and activator of Transcription (STAT3). In this study, we found that the inositol requiring kinase (IRE) 1alpha/X-box binding protein (XBP1) axis of UPR plays a key role in the survival of PEL cells, while double stranded RNA-activated protein kinase-like ER kinase (PERK) and activating transcription factor (ATF) 6 slightly influence it, in correlation with the capacity of the IRE1alpha/XBP1 axis to induce the release of interleukin (IL)-6, IL-10 and Vascular-Endothelial Growth Factor (VEGF). Moreover, we found that IRE1alpha/XBP1 inhibition reduced STAT3 Tyr705 phosphorylation and induced a pro-survival autophagy in PEL cells. In conclusion, this study suggests that targeting the IRE1alpha/XBP1 axis represents a promising strategy against PEL cells and that the cytotoxic effect of this treatment may be potentiated by autophagy inhibition.

A Regulatory Loop of FBXW7-MYC-PLK1 Controls Tumorigenesis of MYC-Driven Medulloblastoma

Polo-like kinase 1 (PLK1) is highly expressed in group 3 medulloblastoma (MB), and it has been preclinically validated as a cancer therapeutic target in medulloblastoma. Here, we demonstrate that PLK1 inhibition with PCM-075 or BI6727 significantly reduces the growth of MB cells and causes a decrease of c-MYC mRNA and protein levels. We show that MYC activates PLK1 transcription, while the inhibition of PLK1 suppresses MB tumor development and causes a decrease in c-MYC protein level by suppressing FBXW7 auto poly-ubiquitination. FBXW7 physically interacts with PLK1 and c-MYC, facilitating their protein degradation by promoting ubiquitination. These results demonstrate a PLK1-FBXW7-MYC regulatory loop in MYC-driven medulloblastoma. Moreover, FBXW7 is significantly downregulated in group 3 patient samples. The overexpression of FBXW7 induced apoptosis and suppressed proliferation in vitro and in vivo, while constitutive phosphorylation mutation attenuated its tumor suppressor function. Altogether, these findings demonstrated that PLK1 inhibition stabilizes FBXW7 in MYC-driven MB, thus revealing an important function of FBXW7 in suppressing medulloblastoma progression.

Constitutive activation of the EGFR–STAT1 axis increases proliferation of meningioma tumor cells

Background Meningiomas are the most frequent primary brain tumors of the central nervous system. The standard of treatment is surgery and radiotherapy, but effective pharmacological options are not available yet. The well-characterized genetic background stratifies these tumors in several subgroups, thus increasing diversification. We identified epidermal growth factor receptor–signal transducer and activator of transcription 1 (EGFR–STAT1) overexpression and activation as a common identifier of these tumors. Methods We analyzed STAT1 overexpression and phosphorylation in 131 meningiomas of different grades and locations by utilizing several techniques, including Western blots, qPCR, and immunocytochemistry. We also silenced and overexpressed wild-type and mutant forms of the gene to assess its biological function and its network. Results were further validated by drug testing. Results STAT1 was found widely overexpressed in meningioma but not in the corresponding healthy controls. The protein showed constitutive phosphorylation not dependent on the JAK–STAT pathway. STAT1 knockdown resulted in a significant reduction of cellular proliferation and deactivation of AKT and ERK1/2. STAT1 is known to be activated by EGFR, so we investigated the tyrosine kinase and found that EGFR was also constitutively phosphorylated in meningioma and was responsible for the aberrant phosphorylation of STAT1. The pharmaceutical inhibition of EGFR caused a significant reduction in cellular proliferation and of overall levels of cyclin D1, pAKT, and pERK1/2. Conclusions STAT1–EGFR-dependent constitutive phosphorylation is responsible for a positive feedback loop that causes its own overexpression and consequently an increased proliferation of the tumor cells. These findings provide the rationale for further studies aiming to identify effective therapeutic options in meningioma.