Atp8a1 deletion increases the proliferative activity of hematopoietic stem cells by impairing PTEN function.

PURPOSE: The eukaryotic cell plasma membrane contains several asymmetrically distributed phospholipids, which is maintained by the P4-ATPase flippase complex. Herein, we demonstrated the biological effects and mechanisms of asymmetrical loss in hematopoietic stem cells (HSCs). METHODS: An Atp8a1 knockout mouse model was employed, from which the HSC (long-term HSCs and short-term HSCs) population was analyzed to assess their abundance and function. Additionally, competitive bone marrow transplantation and 5-FU stress assays were performed. RNA sequencing was performed on Hematopoietic Stem and Progenitor Cells, and DNA damage was assayed using immunofluorescence staining and comet electrophoresis. The protein abundance for members of key signaling pathways was confirmed using western blotting. RESULTS: Atp8a1 deletion resulted in slight hyperleukocytosis, associated with the high proliferation of HSCs and BCR/ABL1 transformed leukemia stem cells (LSCs). Atp8a1 deletion increased the repopulation capability of HSCs with a competitive advantage in reconstitution assay. HSCs without Atp8a1 were more sensitive to 5-FU-induced apoptosis. Moreover, Atp8a1 deletion prevented HSC DNA damage and facilitated DNA repair processes. Genes involved in PI3K-AKT-mTORC1, DNA repair, and AP-1 complex signaling were enriched and elevated in HSCs with Atp8a1 deletion. Furthermore, Atp8a1 deletion caused decreased PTEN protein levels, resulting in the activation of PI3K-AKT-mTORC1 signaling, further increasing the activity of JNK/AP-1 signaling and YAP1 phosphorylation. CONCLUSION: We identified the role of Atp8a1 on hematopoiesis and HSCs. Atp8a1 deletion resulted in the loss of phosphatidylserine asymmetry and intracellular signal transduction chaos.

TSPAN32 suppresses chronic myeloid leukemia pathogenesis and progression by stabilizing PTEN.

We report herein that TSPAN32 is a key node factor for Philadelphia (Ph+) leukemia pathogenesis. We found that TSPAN32 expression was repressed by BCR-ABL and ectopic TSPAN32 expression upon Imatinib treatment inhibited the proliferation of Ph+ cell lines. Tspan32 overexpression significantly prevented BCR-ABL induced leukemia progression in a murine model and impaired leukemia stem cell (LSC) proliferation. LSCs represent an obstacle for chronic myeloid leukemia (CML) elimination, which continually replenish leukemia cells and are associated with disease relapse. Therefore, the identification of essential targets that contribute to the survival and self-renewal of LSCs is important for novel curative CML. Mechanistically, TSPAN32 was shown to interact with PTEN, increased its protein level and caused a reduction in PI3K-AKT signaling activity. We also found that TSPAN32 was repressed by BCR-ABL via the suppression of an important transcription factor, TAL1. Ectopic expression of TAL1 significantly increased TSPAN32 mRNA and protein level, which indicated that BCR-ABL repressed TSPAN32 transcription by decreasing TAL1 expression. Overall, we identified a new signaling axis composed of "BCR-ABL-TAL1-TSPAN32-PTEN-PI3K-AKT". Our findings further complement the known mechanisms underlying the transformation potential of BCR-ABL in CML pathogenesis. This new signaling axis also provides a potential means to target PI3K-AKT for CML treatment.

FLI1 accelerates leukemogenesis through transcriptional regulation of pyruvate kinase-L/R and other glycolytic genes.

In cancer cells, multiple oncogenes and tumor suppressors control glycolysis to sustain rapid proliferation. The ETS-related transcription factor Fli1 plays a critical role in the induction and progression of leukemia, yet, the underlying mechanism of this oncogenic event is still not fully understood. In this study, RNAseq analysis of FLI1-depleted human leukemic cells revealed transcriptional suppression of the PKLR gene and activation of multiple glycolytic genes, such as PKM1/2. Pharmacological inhibition of glycolysis by PKM2 inhibitor, Shikonin, significantly suppressed leukemic cell proliferation. FLI1 directly binds to the PKLR promoter, leading to the suppression of this inhibitor of glycolysis. In accordance, shRNA-mediated depletion of PKLR in leukemic HEL cells expressing high levels of FLI1 accelerated leukemia proliferation, pointing for the first time to its tumor suppressor function. PKLR knockdown also led to downregulation of the erythroid markers EPOR, HBA1, and HBA2 and suppression of erythroid differentiation. Interestingly, silencing of PKLR in HEL cells significantly increased FLI1 expression, which was associated with faster proliferation in culture. In FLI1-expressing leukemic cells, lower PKLR expression was associated with higher expression of PKM1 and PKM2, which promote aerobic glycolysis. Finally, injection of pyruvate, a known inhibitor of glycolysis, into leukemia mice significantly suppressed leukemogenesis. These results demonstrate that FLI1 promotes leukemia in part by inducing glycolysis, implicates PKLR in erythroid differentiation, and suggests that targeting glycolysis may be an attractive therapeutic strategy for cancers driven by FLI1 overexpression.

The suppressive functions of Rora in B lineage cell proliferation and BCR/ABL1-induced B-ALL pathogenesis.

RORA plays an important role in regulating circadian rhythms, inflammation, metabolism and cellular development. Herein, we explore the roles of Rora in B cell proliferation and differentiation, as well as in Ph+ B-ALL. By using Roraloxp/loxp Mx-1-Cre mice, Rora was deleted in hematopoietic cells post Pipc induction. Rora deficiency mice were associated with an obvious accumulation of B cells in the peripheral blood, bone marrow, and spleen. On the other hand, activation of Rora with Cholesterol sulfate (CS) was associated with decreased B cell numbers. RNA-seq analysis revealed that the transcription level of Lmo1 was decreased in Rora deficient B cells. Moreover, the expression of RORA was shown to be decreased in Ph+ B-ALL cells compared to peripheral blood derived B cells from healthy donors. The overexpression of Rora in BaF3 cells with BCR/ABL1 was also associated with impeded the cell growth and an increased apoptotic rate compared to cells transduced with BCR/ABL1 alone. The co-expression of BCR/ABL1 and Rora induced B-ALL mouse model was associated with the significant inhibition of BCR/ABL1-transformed cell growth and prolonged the survival of the diseased mice. These results suggest a novel role for Rora in B cell development and Ph+ leukemogenesis.

Current insights into the role of Fli-1 in hematopoiesis and malignant transformation.

Fli-1, a member of the ETS family of transcription factors, was discovered in 1991 through retroviral insertional mutagenesis as a driver of mouse erythroleukemias. In the past 30 years, nearly 2000 papers have defined its biology and impact on normal development and cancer. In the hematopoietic system, Fli-1 controls self-renewal of stem cells and their differentiation into diverse mature blood cells. Fli-1 also controls endothelial survival and vasculogenesis, and high and low levels of Fli-1 are implicated in the auto-immune diseases systemic lupus erythematosus and systemic sclerosis, respectively. In addition, aberrant Fli-1 expression is observed in, and is essential for, the growth of multiple hematological malignancies and solid cancers. Here, we review the historical context and latest research on Fli-1, focusing on its role in hematopoiesis, immune response, and malignant transformation. The importance of identifying Fli-1 modulators (both agonists and antagonists) and their potential clinical applications is discussed.

A critical ETV4/Twist1/Vimentin axis in Ha-RAS-induced aggressive breast cancer.

RAS oncogenes are major drivers of diverse types of cancer. However, they are largely not druggable, and therefore targeting critical downstream pathways and dependencies is an attractive approach. We have isolated a tumorigenic cell line (FE1.2), which exhibits mesenchymal characteristics, after inoculating Ha-Ras-expressing retrovirus into mammary glands of rats, and subsequently isolated a non-aggressive revertant cell line (FC5). This revertant has lost the rat Ha-Ras driver and showed a more epithelial morphology, slower proliferation in culture, and reduced tumorigenicity in vivo. Re-expression of human Ha-RAS in these cells (FC5-RAS) reinduced mesenchymal morphology, higher proliferation rate, and tumorigenicity that was still significantly milder than parental FE1.2 cells. RNA-seq analysis of FC5-RAS vs FC5-Vector cells identified multiple genes whose expressions were regulated by Ha-RAS. This analysis also identified many genes including those controlling cell growth whose expression was altered by loss of HA-Ras in FC5 cells but remained unchanged upon reintroduction of Ha-RAS. These results suggest that targeting the Ha-Ras driver oncogene induces partial tumor regression, but it still denotes strong efficacy for cancer therapy. Among the RAS-responsive genes, we identified Twist1 as a critical mediator of epithelial-to-mesenchymal transition through the direct transcriptional regulation of vimentin. Mechanistically, we show that Twist1 is induced by the ETS gene, ETV4, downstream of Ha-RAS, and that inhibition of ETV4 suppressed the growth of breast cancer cells driven by the Ha-RAS pathway. Targeting the ETV4/Twist1/Vimentin axis may therefore offer a therapeutic modality for breast tumors driven by the Ha-RAS pathway.

FLI1 regulates inflammation-associated genes to accelerate leukemogenesis.

Inflammation plays a critical role in cancer initiation and progression, and is induced by inflammatory factors that are direct target of oncogenes and tumor suppressors. The ETS related transcription factor Fli-1 is involved in the induction and progression of various cancers; yet its role in inflammation is not well-defined. Using RNAseq analysis, we herein demonstrate that FLI1 induces the inflammatory pathway in erythroleukemia cells. Majority of genes within the TNF signaling pathway including TNF and IL1B were identified as transcriptional targets of FLI1. TNF expression is indirectly regulated by FLI1 through upregulation of another ETS related oncogene, SPI1/PU.1. Pharmacological inhibition of TNF significantly inhibited leukemia cell proliferation in culture. In contrast, IL1B expression is directly regulated by FLI1 through promoter binding and transcriptional activation. The secreted factor IL1B binds its canonical receptors to accelerate cancer progression through changes in the surrounding tumor microenvironment, fostering cell survival, proliferation and migration. Through network analysis, we identified IL1B-interacting genes whose expression is also regulated by FLI1. Among these, IL1B-interacting proteins, FOS, JUN, JUNB and CASP1 are negatively regulated by FLI1. Treatment of leukemia cells with inhibitors of AP1 (TAN IIA) and CASP1 (765VX) significantly accelerated FLI1-dependent leukemia progression. These results emphasize the significance of FLI1 in regulating the inflammatory pathway. Targeting these inflammatory genes downstream of FLI1 offers a novel strategy to treat leukemic progression associated with overexpression of this oncogenic ETS transcription factor.

Propofol mediates pancreatic cancer cell activity through the repression of ADAM8 via SP1.

Propofol is a commonly used anesthetic with controversial effects on cancer cells. A growing number of studies have demonstrated that low concentrations of propofol are associated with tumor suppression and when used as an intravenous anesthesia improved recurrence­free survival rates for many cancers, but deeper insights into its underlying mechanism are needed. The study detailed herein focused upon the effect of propofol on pancreatic cancer cells and the mechanism by which propofol reduces A disintegrin and metalloproteinase 8 (ADAM8) expression. The ability of propofol to impact the proliferation, migration and cell cycle of pancreatic cancer cell lines was assessed in vitro. This was mechanistically explored following the identification of SP1 binding sites within ADAM8, which enabled the regulatory effects of specificity protein 1 (SP1) on ADAM8 following propofol treatment to be further explored. Ultimately, this study was able to show that propofol significantly inhibited the proliferation, migration and invasion of pancreatic cancer cells and decreased the percentage of cells in S­phase. Propofol treatment was also shown to repress ADAM8 and SP1 expression, but was unable to affect ADAM8 expression following knockdown of SP1. Moreover, a direct physical interaction between SP1 and ADAM8 was verified using co­immunoprecipitation and dual­luciferase reporter assays. Cumulatively, these results suggest that propofol represses pathological biological behaviors associated with pancreatic cancer cells through the suppression of SP1, which in turn results in lower ADAM8 mRNA expression and protein levels.

ERK activation via A1542/3 limonoids attenuates erythroleukemia through transcriptional stimulation of cholesterol biosynthesis genes.

BACKGROUND: Cholesterol plays vital roles in human physiology; abnormal levels have deleterious pathological consequences. In cancer, elevated or reduced expression of cholesterol biosynthesis is associated with good or poor prognosis, but the underlying mechanisms are largely unknown. The limonoid compounds A1542 and A1543 stimulate ERK/MAPK by direct binding, leading to leukemic cell death and suppression of leukemia in mouse models. In this study, we investigated the downstream consequences of these ERK/MAPK agonists in leukemic cells. METHODS: We employed RNAseq analysis combined with Q-RT-PCR, western blot and bioinformatics to identify and confirm genes whose expression was altered by A1542 and A1543 in leukemic cells. ShRNA lentiviruses were used to silence gene expression. Cell culture and an animal model (BALB/c) of erythroleukemia induced by Friend virus were utilized to validate effects of cholesterol on leukemia progression. RESULTS: RNAseq analysis of A1542-treated cells revealed the induction of all 18 genes implicated in cholesterol biosynthesis. Expression of these cholesterol genes was blocked by cedrelone, an ERK inhibitor. The cholesterol inhibitor lovastatin diminished ERK/MAPK activation by A1542, thereby reducing leukemic cell death induced by this ERK1/2 agonist. Growth inhibition by cholesterol was observed both at the intracellular level, and when orally administrated into a leukemic mouse model. Both HDL and LDL also suppressed leukemogenesis, implicating these lipids as important prognostic markers for leukemia progression. Mechanistically, knockdown experiments revealed that the activation of SREBP1/2 by A1542-A1543 was responsible for induction of only a sub-set of cholesterol biosynthesis genes. Induction of other regulatory factors by A1542-A1543 including EGR1, AP1 (FOS + JUN) LDLR, IER2 and others may cooperate with SREBP1/2 to induce cholesterol genes. Indeed, pharmacological inhibition of AP1 significantly inhibited cholesterol gene expression induced by A1542. In addition to leukemia, high expression of cholesterol biosynthesis genes was found to correlate with better prognosis in renal cancer. CONCLUSIONS: This study demonstrates that ERK1/2 agonists suppress leukemia and possibly other types of cancer through transcriptional stimulation of cholesterol biosynthesis genes.

FLI1 Induces Megakaryopoiesis Gene Expression Through WAS/WIP-Dependent and Independent Mechanisms; Implications for Wiskott-Aldrich Syndrome.

Wiskott-Aldrich Syndrome, WAS/WAVE, is a rare, X-linked immune-deficiency disease caused by mutations in the WAS gene, which together with its homolog, N-WASP, regulates actin cytoskeleton remodeling and cell motility. WAS patients suffer from microthrombocytopenia, characterized by a diminished number and size of platelets, though the underlying mechanism is not fully understood. Here, we identified FLI1 as a direct transcriptional regulator of WAS and its binding partner WIP. Depletion of either WAS or WIP in human erythroleukemic cells accelerated cell proliferation, suggesting tumor suppressor function of both genes in leukemia. Depletion of WAS/WIP also led to a significant reduction in the percentage of CD41 and CD61 positive cells, which mark committed megakaryocytes. RNAseq analysis revealed common changes in megakaryocytic gene expression following FLI1 or WASP knockdown. However, in contrast to FLI1, WASP depletion did not alter expression of late-stage platelet-inducing genes. N-WASP was not regulated by FLI1, yet its silencing also reduced the percentage of CD41+ and CD61+ megakaryocytes. Moreover, combined knockdown of WASP and N-WASP further suppressed megakaryocyte differentiation, indicating a major cooperation of these related genes in controlling megakaryocytic cell fate. However, unlike WASP/WIP, N-WASP loss suppressed leukemic cell proliferation. WASP, WIP and N-WASP depletion led to induction of FLI1 expression, mediated by GATA1, and this may mitigate the severity of platelet deficiency in WAS patients. Together, these results uncover a crucial role for FLI1 in megakaryocyte differentiation, implicating this transcription factor in regulating microthrombocytopenia associated with Wiskott-Aldrich syndrome.

Ubash3b promotes TPA-mediated suppression of leukemogenesis through accelerated downregulation of PKCδ protein.

Acquired drug-resistance, often involving downregulation or mutations in the target protein, is a major caveat in precision medicine. Understanding mechanisms of resistance to therapeutic drugs may unravel strategies to overcome or prevent them. We previously identified phorbol ester (PE) compounds such as TPA that induce Protein Kinase δ (PKCδ), thereby suppressing leukemogenesis. Here we identified erythroleukemia cell lines that resist PEs and showed that reduced PKCδ protein expression underlies drug resistance. Reduced level of PKCδ in resistant cell lines was due to its phosphorylation followed by protein degradation. Indeed, proteasome inhibition prevented PE-induced loss of PKCδ. Accordingly, a combination of TPA and the proteasome inhibitor ALLN significantly suppressed leukemia in a mouse model of leukemia. PKCδ downregulation by TPA was independent of the downstream MAPK/ERK/P38/JNK pathway. Instead, expression of ubiquitin-associated and SH3 domain-containing protein b (Ubash3b) was induced by TPA, which leads to PKCδ protein dephosphorylation and degradation. This specific degradation was blocked by RNAi-mediated depletion of Ubash3b. In drug-sensitive leukemic cells, TPA did not induce Ubash3b, and consequently, PKCδ levels remained high. A PE-resistant cell line derived from PE-treated sensitive cells exhibited very low PKCδ expression. In these drug resistance cells, a Ubash3b independent mechanism led to PKCδ degradation. Thus, PE compounds in combination with proteasome or specific inhibitors for Ubash3b, or other factors can overcome resistance to TPA, leading to durable suppression of leukemic growth. These results identify Ubash3b as a potential target for drug development.

A C21-steroidal derivative suppresses T-cell lymphoma in mice by inhibiting SIRT3 via SAP18-SIN3.

The SIN3 repressor complex and the NAD-dependent deacetylase SIRT3 control cell growth, and development as well as malignant transformation. Even then, a little known about cross-talks between these two chromatin modifiers or whether their interaction explored therapeutically. Here we describe the identification of a C21-steroidal derivative compound, 3-O-chloroacetyl-gagamine, A671, which potently suppresses the growth of mouse and human T-cell lymphoma and erythroleukemia in vitro and preclinical models. A671 exerts its anti-neoplastic effects by direct interaction with Histone deacetylase complex subunit SAP18, a component of the SIN3 suppressor complex. This interaction stabilizes and activates SAP18, leading to transcriptional suppression of SIRT3, consequently to inhibition of proliferation and cell death. The resistance of cancer cells to A671 correlated with diminished SAP18 activation and sustained SIRT3 expression. These results uncover the SAP18-SIN3-SIRT3 axis that can be pharmacologically targeted by a C21-steroidal agent to suppress T-cell lymphoma and other malignancies.

Characterization of the transcriptional response of Candida parapsilosis to the antifungal peptide MAF-1A.

Candida parapsilosis is a major fungal pathogen that leads to sepsis. New and more effective antifungal agents are required due to the emergence of resistant fungal strains. MAF-1A is a cationic antifungal peptide isolated from Musca domestica that is effective against a variety of Candida species. However, the mechanism(s) of its antifungal activity remains undefined. Here, we used RNA-seq to identify differentially expressed genes (DEGs) in Candida parapsilosis following MAF-1A exposure. The early (6 h) response included 1,122 upregulated and 1,065 downregulated genes. Late (18 h) responses were associated with the increased expression of 101 genes and the decreased expression of 151 genes. Upon MAF-1A treatment for 18 h, 42 genes were upregulated and 25 genes were downregulated. KEGG enrichment showed that the DEGs in response to MAF-1A were mainly involved in amino acid synthesis and metabolism, oxidative phosphorylation, sterol synthesis, and apoptosis. These results indicate that MAF-1A exerts antifungal activity through interference with Candida parapsilosis cell membrane integrity and organelle function. This provides new insight into the interaction between Candida parapsilosis and this antimicrobial peptide and serves as a reference for future Candida parapsilosis therapies.

Whole Exome Sequencing Identifies Candidate Genes Associated with Hereditary Predisposition to Uveal Melanoma.

PURPOSE: To identify susceptibility genes associated with hereditary predisposition to uveal melanoma (UM) in patients with no detectable germline BAP1 alterations. DESIGN: Retrospective case series from academic referral centers. PARTICIPANTS: Cohort of 154 UM patients with high risk of hereditary cancer defined as patients with 1 or more of the following: (1) familial UM, (2) young age (<35 years) at diagnosis, (3) personal history of other primary cancers, and (4) family history of 2 or more primary cancers with no detectable mutation or deletion in BAP1 gene. METHODS: Whole exome sequencing, a cancer gene panel, or both were carried out. Probands included 27 patients with familial UM, 1 patient with bilateral UM, 1 patient with congenital UM, and 125 UM patients with strong personal or family histories, or both, of cancer. Functional validation of variants was carried out by immunohistochemistry, reverse-transcriptase polymerase chain reaction, and genotyping. MAIN OUTCOME MEASURES: Clinical characterization of UM patients with germline alterations in known cancer genes. RESULTS: We identified actionable pathogenic variants in 8 known hereditary cancer predisposition genes (PALB2, MLH1, MSH6, CHEK2, SMARCE1, ATM, BRCA1, and CTNNA1) in 9 patients, including 3 of 27 patients (11%) with familial UM and 6 of 127 patients (4.7%) with a high risk for cancer. Two patients showed pathogenic variants in CHEK2 and PALB2, whereas variants in the other genes each occurred in 1 patient. Biallelic inactivation of PALB2 and MLH1 was observed in tumors from the respective patients. The frequencies of pathogenic variants in PALB2, MLH1, and SMARCE1 in UM patients were significantly higher than the observed frequencies in noncancer controls (PALB2: P = 0.02; odds ratio, 8.9; 95% confidence interval, 1.5-30.6; MLH1: P = 0.04; odds ratio, 25.4; 95% confidence interval, 1.2-143; SMARCE1: P = 0.001; odds ratio, 2047; 95% confidence interval, 52-4.5e15, respectively). CONCLUSIONS: The study provided moderate evidence of gene and disease association of germline mutations in PALB2 and MLH1 with hereditary predisposition to UM. It also identified several other candidate susceptibility genes. The results suggest locus heterogeneity in predisposition to UM. Genetic testing for hereditary predisposition to cancer is warranted in UM patients with strong personal or family history of cancers, or both.

DNA repair gene expression is associated with differential prognosis between HPV16 and HPV18 positive cervical cancer patients following radiation therapy.

Cervical cancers are almost always induced by HPV infections, of which HPV16 and HPV18 are predominant. Cancers associated with these strains are induced through DNA repair factors and have a differential response to radiation therapy. Hence this study focuses on finding DNA repair gene expression differences in HPV16 and HPV18 positive cervical cancers after radiation therapy. A higher number of somatic mutations were observed in HPV16 positive cervical tumours for patients that were disease free when compared to those who recurred/progressed. Moreover, hierarchal clustering of RNAseq data from The Cancer Genome Atlas was conducted to identify groups of DNA repair genes associated with a differential prognosis for cervical cancer following postoperative radiation therapy. TP53BP1, MCM9 (at higher than mean levels), POLR2F and SIRT6 (at lower than mean levels), were associated with an increase in patients experiencing cervical cancer recurrence/progression following postoperative radiation therapy when HPV18 positive, but not HPV16 positive. The expression patterns of these genes provide an explanation for the higher rate of postoperative radiation therapy resistance associated with HPV18 positive cervical cancer patients. Therefore, HPV18 positive cervical tumours may be more likely retain a greater non-homologous end joining and homologous recombination pathway activity, which could dampen the effect of postoperative radiation therapy. Moreover, greater susceptibility to postoperative radiation therapy could be caused by the reliance of cervical cancer cells upon the single-strand annealing and nucleotide excision pathways for repair of DNA damage.

Erythropoietin Signaling in the Microenvironment of Tumors and Healthy Tissues.

Erythropoietin (EPO), the primary cytokine of erythropoiesis, stimulates both proliferation and differentiation of erythroid progenitors and their maturation to red blood cells. Basal EPO levels maintain the optimum levels of circulating red blood cells. However, during hypoxia, EPO secretion and its expression is elevated drastically in renal interstitial fibroblasts, thereby increasing the number of erythroid progenitors and accelerating their differentiation to mature erythrocytes. A tight regulation of this pathway is therefore of paramount importance. The biological response to EPO is commenced through the involvement of its cognate receptor, EPOR. The receptor-ligand complex results in homodimerization and conformational changes, which trigger downstream signaling events and cause activation or inactivation of critical transcription factors that promote erythroid expansion. In recent years, recombinant human EPO (rEPO) has been widely used as a therapeutic tool to treat a number of anemias induced by infection, and chemotherapy for various cancers. However, several studies have uncovered a tumor promoting ability of EPO in man, which likely occurs through EPOR or alternative receptor(s). On the other hand, some studies have demonstrated a strong anticancer activity of EPO, although the mechanism still remains unclear. A thorough investigation of EPOR signaling could yield enhanced understanding of the pathobiology for a variety of disorders, as well as the potential novel therapeutic strategies. In this chapter, in addition to the clinical relevance of EPO/EPOR signaling, we review its anticancer efficacy within various tumor microenvironments.

FLI1 promotes protein translation via the transcriptional regulation of MKNK1 expression.

The disruption of protein translation machinery is a common feature of cancer initiation and progression, and drugs that target protein translation offer new avenues for therapy. The translation initiation factor, eukaryotic initiation factor 4E (eIF4E), is induced in a number of cancer cell lines and is one such candidate for therapeutic intervention. Friend leukemia integration 1 (FLI1) is a potent oncogenic transcription factor that promotes various types of cancer by promoting several hallmarks of cancer progression. FLI1 has recently been implicated in protein translation through yet unknown mechanisms. This study identified a positive association between FLI1 expression and mitogen­activated protein kinase (MAPK)­interacting serine/threonine kinase1 (MKNK1), the immediate upstream regulator of the eIF4E initiation factor. The short hairpin RNA (shRNA)­mediated silencing or overexpression of FLI1 in leukemic cell lines downregulated or upregulated MKNK1 expression, respectively. Promoter analysis identified a potent FLI1 binding site in the regulatory region of the MKNK1 promoter. In transient transfection experiments, FLI1 increased MKNK1 promoter activity, which was blocked by mutating the FLI1 binding site. FLI1 specifically affected the expression of MKNK1, but not that of MKNK2. The siRNA­mediated downregulation of MKNK1 downregulated the expression of survivin (BIRC5) and significantly suppressed cell proliferation in culture. FLI1 inhibitory compounds were shown to downregulate this oncogene through the suppression of MAPK/extracellular­regulated kinase (ERK) signaling and the subsequent activation of miR­145, leading to a lower MKNK1 expression and the suppression of leukemic growth. These results uncover a critical role for FLI1 in the control of protein translation and the importance of targeting its function and downstream mediators, such as MKNK1, for cancer therapy.

Heterogeneity in Mitogen-Activated Protein Kinase (MAPK) Pathway Activation in Uveal Melanoma With Somatic GNAQ and GNA11 Mutations.

Purpose: The activation of the mitogen-activated protein kinase (MAPK) pathway has been suggested as the major downstream target when GNAQ and GNA11 (GNAQ/11) are mutated in uveal melanoma (UM). However, clinical trials with single agent MEK inhibitor showed no clinical significance in altering the overall outcome of the disease in UM; therefore, we investigated the correlation between naturally occurring mutations in GNAQ/11 and activation of MAPK pathway in vivo in primary UM. Methods: Screening for activating mutations in codons 183 and 209 of GNAQ/11 was carried out by sequencing and restriction fragment length polymorphism (RFLP) in a cohort of 42 primary UM. Activation of the MAPK pathway and other potential downstream signals was assessed by immunohistochemistry and/or Western blot analysis. Potential downstream signaling of mutant and wild type GNAQ/11 was studied by transient transfection assay in nonmutant cell lines. Results: Somatic mutations in GNAQ/11 were observed in 35/42 (83.3%) of primary UM. Tumors with GNAQ/11 mutations showed variations in the activation of ERK1/2 with significant tumor heterogeneity. Weak and undetectable ERK1/2 activation was observed in 4/35 (11.4%) and 8/35 (22.9%) of the GNAQ/11 mutant UM, respectively. Tumor heterogeneity of GNAQ/11 mutations was also observed in a subset of tumors. Conclusions: Our results indicate that there is marked variation in MAPK activation in UM with GNAQ/11 mutations. Thus, GNAQ/11 mutational status is not a sufficient biomarker to adequately predict UM patient responses to single-agent selective MEK inhibitor therapy.

Analysis of the exome aggregation consortium (ExAC) database suggests that the BAP1-tumor predisposition syndrome is underreported in cancer patients.

The BAP1-tumor predisposition syndrome (BAP1-TPDS) has been recently identified to predispose patients to a variety of cancers and preneoplastic lesions. About 130 unrelated probands have been identified worldwide; however, the impact of the syndrome is suspected to be much larger given the diversity of the cancer phenotype. To evaluate the frequency of germline BAP1 mutations in the general and cancer populations, we analyzed the Exome Aggregation Consortium (ExAC), a database that contains 53105 exomes of unrelated individuals unaffected by cancer (general population) and exomes of 7601 unrelated individuals affected by cancer provided by the Cancer Genome Atlas (TCGA, cancer subjects). BAP1 null variants were seen at much higher frequency in the cancer subjects (0.0526%) compared to the general population (0.00188%) with a relative risk of 27.93 and (P = 0.0011, [95% CI: 3.122-249.883], Fisher's exact test). We also studied a reported BAP1 null variant, c.1203T > G, p.T401* (rs200156887), observed commonly in the general population. Sequencing and restriction fragment polymorphism of the RT-4 cell line that contains this variant revealed that it is in fact a 3bp deletion/insertion, c.1201_1203delinsGAG, a likely benign missense alteration p.Y401E explaining the relative high frequency of this variant in the general population. In conclusion, germline null mutations in BAP1 have a significantly higher frequency in cancer patients than the general population. Given the low frequency of reported families with BAP1-TPDS, our results suggest that the syndrome is underreported especially in patients with cancer.

Shear stress regulated gene expression and angiogenesis in vascular endothelium.

The behavior of vascular EC is greatly altered in sites of pathological angiogenesis, such as a developing tumor or atherosclerotic plaque. Until recently it was thought that this was largely due to abnormal chemical signaling, i.e., endothelial cell chemo transduction, at these sites. However, we now demonstrate that the shear stress intensity encountered by EC can have a profound impact on their gene expression and behavior. We review the growing body of evidence suggesting that mechanotransduction, too, is a major regulator of pathological angiogenesis. This fits with the evolving story of physiological angiogenesis, where a combination of metabolic and mechanical signaling is emerging as the probable mechanism by which tight feedback regulation of angiogenesis is achieved in vivo.