NSD1 supports cell growth and regulates autophagy in HPV-negative head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Despite advances in therapeutic management and immunotherapy, the 5-year survival rate for head and neck cancer remains at ~66% of all diagnosed cases. A better definition of drivers of HPV-negative HNSCC that are targetable points of tumor vulnerability could lead to significant clinical advances. NSD1 is a histone methyltransferase that catalyzes histone H3 lysine 36 di-methylation (H3K36me2); mutations inactivating NSD1 have been linked to improved outcomes in HNSCC. In this study, we show that NSD1 induces H3K36me2 levels in HNSCC and that the depletion of NSD1 reduces HNSCC of cell growth in vitro and in vivo. We also find that NSD1 strongly promotes activation of the Akt/mTORC1 signaling pathway. NSD1 depletion in HNSCC induces an autophagic gene program activation, causes accumulation of the p62 and LC3B-II proteins, and decreases the autophagic signaling protein ULK1 at both protein and mRNA levels. Reflecting these signaling defects, the knockdown of NSD1 disrupts autophagic flux in HNSCC cells. Taken together, these data identify positive regulation of Akt/mTORC1 signaling and autophagy as novel NSD1 functions in HNSCC, suggesting that NSD1 may be of value as a therapeutic target in this cancer.

NSD1 supports cell growth and regulates autophagy in HPV-negative head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Despite advances in therapeutic management and immunotherapy, the five-year survival rate for head and neck cancer remains at ~66% of all diagnosed cases. A better definition of drivers of HPV-negative HNSCC that are targetable points of tumor vulnerability could lead to significant clinical advances. NSD1 is a histone methyltransferase which catalyzes histone H3 lysine 36 di-methylation (H3K36me2); mutations inactivating NSD1 have been linked to improved outcomes in HNSCC. In this study, we show that NSD1 induces H3K36me2 levels in HNSCC, and that the depletion of NSD1 reduces HNSCC of cell growth in vitro and in vivo. We also find that NSD1 strongly promotes activation of the Akt/mTORC1 signaling pathway. NSD1 depletion in HNSCC induces an autophagic gene program activation, causes accumulation of the p62 and LC3B-II proteins, and decreases the autophagic signaling protein ULK1 at both protein and mRNA levels. Reflecting these signaling defects, knockdown of NSD1 disrupts autophagic flux in HNSCC cells. Taken together, these data identify positive regulation of Akt/mTORC1 signaling and autophagy as novel NSD1 functions in HNSCC, suggesting that NSD1 may be of value as a therapeutic target in this cancer.

Musashi-2 (MSI2) regulation of DNA damage response in lung cancer

Lung cancer is one of the most common types of cancers worldwide. Non-small cell lung cancer (NSCLC), typically caused by KRAS and TP53 driver mutations, represents the majority of all new lung cancer diagnoses. Overexpression of the RNA-binding protein (RBP) Musashi-2 (MSI2) has been associated with NSCLC progression. To investigate the role of MSI2 in NSCLC development, we compared the tumorigenesis in mice with lung-specific Kras -activating mutation and Trp53 deletion, with and without Msi2 deletion (KP versus KPM2 mice). KPM2 mice showed decreased lung tumorigenesis in comparison with KP mice what supports published data. In addition, using cell lines from KP and KPM2 tumors, and human NSCLC cell lines, we found that MSI2 directly binds ATM/Atm mRNA and regulates its translation. MSI2 depletion impaired DNA damage response (DDR) signaling and sensitized human and murine NSCLC cells to treatment with PARP inhibitors in vitro and in vivo . Taken together, we conclude that MSI2 supports lung tumorigenesis, in part, by direct positive regulation of ATM protein expression and DDR. This adds the knowledge of MSI2 function in lung cancer development. Targeting MSI2 may be a promising strategy to treat lung cancer.

Significance

This study shows the novel role of Musashi-2 as regulator of ATM expression and DDR in lung cancer.

Regulation of VEGFR2 and AKT Signaling by Musashi-2 in Lung Cancer

Lung cancer is the most frequently diagnosed cancer type and the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) represents most of the diagnoses of lung cancer. Vascular endothelial growth factor receptor-2 (VEGFR2) is a member of the VEGF family of receptor tyrosine kinase proteins, which are expressed on both endothelial and tumor cells, are one of the key proteins contributing to cancer development, and are involved in drug resistance. We previously showed that Musashi-2 (MSI2) RNA-binding protein is associated with NSCLC progression by regulating several signaling pathways relevant to NSCLC. In this study, we performed Reverse Protein Phase Array (RPPA) analysis of murine lung cancer, which suggests that VEGFR2 protein is strongly positively regulated by MSI2. Next, we validated VEGFR2 protein regulation by MSI2 in several human lung adenocarcinoma cell line models. Additionally, we found that MSI2 affected AKT signaling via negative PTEN mRNA translation regulation. In silico prediction analysis suggested that both VEGFR2 and PTEN mRNAs have predicted binding sites for MSI2. We next performed RNA immunoprecipitation coupled with quantitative PCR, which confirmed that MSI2 directly binds to VEGFR2 and PTEN mRNAs, suggesting a direct regulation mechanism. Finally, MSI2 expression positively correlated with VEGFR2 and VEGF-A protein levels in human lung adenocarcinoma samples. We conclude that the MSI2/VEGFR2 axis contributes to lung adenocarcinoma progression and is worth further investigations and therapeutic targeting.

Regulation of VEGFR2 and AKT signaling by Musashi-2 in lung cancer

Lung cancer is the most frequently diagnosed cancer type and the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) represents most of the lung cancer. Vascular endothelial growth factor receptor-2 (VEGFR2) is a member of the VEGF family of receptor tyrosine kinase proteins, expressed on both endothelial and tumor cells which is one of the key proteins contributing to cancer development and involved in drug resistance. We previously showed that Musashi-2 (MSI2) RNA-binding protein is associated with NSCLC progression by regulating several signaling pathways relevant to NSCLC. In this study, we performed Reverse Protein Phase Array (RPPA) analysis of murine lung cancer which nominated VEGFR2 protein as strongly positively regulated by MSI2. Next, we validated VEGFR2 protein regulation by MSI2 in several human NSCLC cell line models. Additionally, we found that MSI2 affected AKT signaling via negative PTEN mRNA translation regulation. In silico prediction analysis suggested that both VEGFR2 and PTEN mRNAs have predicted binding sites for MSI2. We next performed RNA immunoprecipitation coupled with quantitative PCR which confirmed that MSI2 directly binds to VEGFR2 and PTEN mRNAs, suggesting direct regulation mechanism. Finally, MSI2 expression positively correlated with VEGFR2 and VEGF-A protein levels in human NSCLC samples. We conclude that MSI2/VEGFR2 axis contributes to NSCLC progression and is worth further investigations and therapeutic targeting.

IL27 Signaling Serves as an Immunologic Checkpoint for Innate Cytotoxic Cells to Promote Hepatocellular Carcinoma

Although inflammatory mechanisms driving hepatocellular carcinoma (HCC) have been proposed, the regulators of anticancer immunity in HCC remain poorly understood. We found that IL27 receptor (IL27R) signaling promotes HCC development in vivo. High IL27EBI3 cytokine or IL27RA expression correlated with poor prognosis for patients with HCC. Loss of IL27R suppressed HCC in vivo in two different models of hepatocarcinogenesis. Mechanistically, IL27R sig-naling within the tumor microenvironment restrains the cytotoxicity of innate cytotoxic lymphocytes. IL27R ablation enhanced their accumulation and activation, whereas depletion or functional impairment of innate cytotoxic cells abrogated the effect of IL27R disruption. Pharmacologic neutralization of IL27 signaling increased infiltration of innate cytotoxic lymphocytes with upregulated cytotoxic molecules and reduced HCC development. Our data reveal an unexpected role of IL27R signaling as an immunologic checkpoint regulating innate cytotoxic lymphocytes and promoting HCC of different etiologies, thus indicating a therapeutic potential for IL27 pathway blockade in HCC.

SIGNIFICANCE

HCC, the most common form of liver cancer, is characterized by a poor survival rate and limited treatment options. The discovery of a novel IL27-dependent mechanism controlling anticancer cytotoxic immune response will pave the road for new treatment options for this devastating disease. This article is highlighted in the In This Issue feature, p. 1825.

Abstract 874: MSI2 regulates VEGFR2 signaling and tumor progression in NSCLC

Lung cancer holds second place in incidence and first place in mortality among all cancers, both in men and women, with metastasis contributing to the vast majority of deaths. Recently, expression of vascular endothelial growth factor receptor-2 (VEGFR2) on both endothelial and tumor cells was demonstrated as one of the key mechanisms contributing to growth of non-small cell lung cancer (NSCLC), the most common subtype of lung cancer. VEGFR2 dependent signaling is critical both for tumor autocrine functions related to NSCLC migration, and in paracrine control of tumor angiogenesis through action on tumor-proximal endothelial cells, suggesting a potential mechanism for growth control. Several drugs targeting VEGFR2 signaling pathway demonstrated their clinical efficacy in NSCLC setting, including VEGFR2 and VEGF-A inhibitors, VEGF-A/PIGF trap. Recently our group demonstrated that RNA-binding protein Musashi-2 (MSI2) is driving progression and metastasis of NSCLC. MSI2 regulates mRNA translation of multiple targets, its expression is upregulated in the metastasis-competent murine and human lung cancer cell lines and is progressively elevated in lung cancer samples. The goal of this study is to define the role of MSI2 in sustaining VEGFR2 signaling during NSCLC progression. Using reverse RNA immunoprecipitation (RIP) qPCR analysis, we demonstrate that MSI2 directly binds VEGFR2 mRNA. Reverse protein phase array (RPPA) of several NSCLC cell line models with expression or knockdown of MSI2 and subsequent direct validation showed that MSI2 strongly and positively regulates expression of VEGFR2. Subsequent mechanistical analysis revealed that MSI2 knockdown leads to decreased VEGFR2 protein and mRNA levels expression in several NSCLC cell lines in vitro, resulting in increased apoptosis via inhibition of VEGFR2 signaling pathway. To better characterize MSI2 biology, we’ve crossed the B6/129S4-Msi2tm1.1Cjl/J (M2) mice with B6/129S/Sv-Krastm3Tyj/J;Trp53tm1Brn/J (KP) mice and generated novel B6/129S/Sv-KP;Msi2-/- (KPM2) mouse model. Induction of tumorigenesis in KP mice using Cre adenovirus leads to development of lung adenocarcinoma. Induction of lung-specific Cre resulted in tumorigenesis in both KP and KPM2 mice. Interestingly, we observed significant decrease in both total lung tumor number and total lung tumor burden in KPM2 compared to KP mice. Next, we established three novel KP and KPM2 derived cell lines from mouse lung tumors and found that KPM2 cell lines demonstrate reduced proliferation capacity and VEGFR2 mRNA level relative to KP cell lines. Additional studies to understand an impact of MSI2 deletion in KP cell lines are ongoing. Taken together, MSI2 is a promising target for NSCLC treatment, as this protein regulates VEGFR2 signaling and apoptosis in cell models and contributes to KP tumorigenesis in vivo.

Citation Format: Igor Bychkov, Alexander Deneka, Iuliia Topchu, Petr Makhov, Alexander Kudinov, Anna Nikonova, John Karanicolas, Erica Golemis, Christopher Lengner, Hossein Borghaei, Jyoti Patel, Yanis Boumber. MSI2 regulates VEGFR2 signaling and tumor progression in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 874.

Abstract 3718: NSD histone methyltransferases drive cell proliferation in HPV-negative head and neck squamous cell carcinoma (HNSCC)

Histone modifications play important role in regulating the function and structure of chromatin. Abnormal histone methylation is often detected during tumor development and progression. NSD1, NSD2, and NSD3 are key histone methyltransferases (HMTs) that catalyze lysine 36 dimethylation (K36me2) at histone H3. Inactivating NSD1 mutations are frequent in head neck squamous cell carcinoma (HNSCC) commonly occur in HPV-negative oropharyngeal (OP) carcinoma and laryngeal carcinomas (LC), and define a novel prognostic subtype in LC, where they associate with dramatically improved overall and progression-free survival. Here, we explored the biological impact of the loss of function of NSD1 in head neck squamous carcinoma (HNSCC). First, we discovered that HNSCC cells with a damaging mutation in NSD1 have reduced K36me2 methylation levels relative to NSD1 wild-type HNSCC cells. Second, we also found slower cell proliferation in NSD1 mutant cell line (SCC4) in comparison with other NSD1 WT cell lines. To further investigate the biologic impact of NSDs, we knocked down NSD1 and NSD2 with shRNA in different histologic subtypes of HNSCC cell lines (JHU011, JHU022, Cal27, and FaDu cell lines). We discovered that depletion of NSD1 and NSD2 results in a reduction of K36me2 and a significant decrease in cell proliferation and clonogenic formation in HNSCC, but not in lung cancer cells. Next, we performed a flow cytometry-based assay and found that NSD1/NSD2 depletion in HNSCC cells causes a significant increase in apoptosis level. We also probed for gene expression and signaling in HNSCC cells following NSD1 depletion using RNA sequencing and reverse protein phase array (RPPA) approaches. From a list of RPPA candidate targets of NSD1, we confirmed the decrease in the protein and mRNA level of Phosphatidylinositol-5-Phosphate 4-Kinase Type 2 Beta (PIP4K2B), but not other members of this family (PIP4K2A and PIP4K2C). PIP4K2B may regulate the ratio of lipid messengers PI5P and PI(4,5)P2 (substrate and reaction product, respectively). The level of phosphorylation of mitogen-activated kinase p70S6 was also decreased under NSD1 knockdown. PIP4K2B siRNA depletion has also led to a significant decrease in HNSCC proliferation. Taken together, this data supports the idea that NSD1 is required for HNSCC cell proliferation via PIP4K2B. Downstream signaling, gene expression effects, and possible cell cycle regulation by NSD enzymes remain to be investigated in more detail. Further, NSDs might be attractive targets for drug development, and targeting NSD1/NSD2 enzymes may be a new strategy for improving outcomes in HNSCC patients.

Citation Format: Iuliia Topchu, Rajendra Pangeni, Igor Bychkov, Petr Makhov, John Karanicolas, Jindan Yu, Erica Golemis, Jochen Lorch, Yanis Boumber. NSD histone methyltransferases drive cell proliferation in HPV-negative head and neck squamous cell carcinoma (HNSCC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3718.

PPP2R2A prostate cancer haploinsufficiency is associated with worse prognosis and a high vulnerability to B55α/PP2A reconstitution that triggers centrosome destabilization

The PPP2R2A gene encodes the B55α regulatory subunit of PP2A. Here, we report that PPP2R2A is hemizygously lost in ~42% of prostate adenocarcinomas, correlating with reduced expression, poorer prognosis, and an increased incidence of hemizygous loss (>75%) in metastatic disease. Of note, PPP2R2A homozygous loss is less common (5%) and not increased at later tumor stages. Reduced expression of B55α is also seen in prostate tumor tissue and cell lines. Consistent with the possibility that complete loss of PPP2R2A is detrimental in prostate tumors, PPP2R2A deletion in cells with reduced but present B55α reduces cell proliferation by slowing progression through the cell cycle. Remarkably, B55α-low cells also appear addicted to lower B55α expression, as even moderate increases in B55α expression are toxic. Reconstitution of B55α expression in prostate cancer (PCa) cell lines with low B55α expression reduces proliferation, inhibits transformation and blocks xenograft tumorigenicity. Mechanistically, we show B55α reconstitution reduces phosphorylation of proteins essential for centrosomal maintenance, and induces centrosome collapse and chromosome segregation failure; a first reported link between B55α/PP2A and the vertebrate centrosome. These effects are dependent on a prolonged metaphase/anaphase checkpoint and are lethal to PCa cells addicted to low levels of B55α. Thus, we propose the reduction in B55α levels associated with hemizygous loss is necessary for centrosomal integrity in PCa cells, leading to selective lethality of B55α reconstitution. Such a vulnerability could be targeted therapeutically in the large pool of patients with hemizygous PPP2R2A deletions, using pharmacologic approaches that enhance PP2A/B55α activity.

IL-27 receptor-regulated stress myelopoiesis drives abdominal aortic aneurysm development

Abdominal aortic aneurysm (AAA) is a prevalent life-threatening disease, where aortic wall degradation is mediated by accumulated immune cells. Although cytokines regulate inflammation within the aorta, their contribution to AAA via distant alterations, particularly in the control of hematopoietic stem cell (HSC) differentiation, remains poorly defined. Here we report a pathogenic role for the interleukin-27 receptor (IL-27R) in AAA, as genetic ablation of IL-27R protects mice from the disease development. Mitigation of AAA is associated with a blunted accumulation of myeloid cells in the aorta due to the attenuation of Angiotensin II (Ang II)-induced HSC expansion. IL-27R signaling is required to induce transcriptional programming to overcome HSC quiescence and increase differentiation and output of mature myeloid cells in response to stress stimuli to promote their accumulation in the diseased aorta. Overall, our studies illuminate how a prominent vascular disease can be distantly driven by a cytokine-dependent regulation of bone marrow precursors.

Abstract 955: Musashi-2 regulates EGFR expression in NSCLC, cell proliferation and survival, response to EGFR inhibitors in EGFR-mutant NSCLC

Musashi-2 (MSI2) is an RNA-binding protein that regulates mRNA translation. We recently established that MSI2 is elevated in a subset of non-small cell lung cancer (NSCLC) tumors upon progression and drives NSCLC metastasis, in part based on activity supporting a TGF-beta/SMAD3/claudin signaling cascade. Here, reverse phase protein array (RPPA) analysis of MSI2-depleted versus control KrasLA1/+;P53R172HΔG/+ murine NSCLC cell lines identified a significant upregulation of HER3 (ERBB3) upon MSI2 depletion. Negative MSI2-dependent regulation of ERBB3 protein was confirmed in multiple murine and human NSCLC models, based on analysis of MSI2 depletion or overexpression. Further, MSI2 positively regulated expression of the epidermal growth factor receptor (EGFR) protein in the same models. Comparing EGFR and KRAS driven models, we found that MSI2 depletion significantly impairs cell proliferation and clonogenicity only in EGFR-mutant NSCLC cell lines. Using RNA immunoprecipitation analysis coupled with qPCR, we show that MSI2 directly binds to EGFR and, to a lesser extent, to HER3 mRNA. MSI2 mRNA binding was correlating with the presence of predicted MSI2 binding sites in corresponding mRNAs. Taken together, this data suggest direct regulation of EGFR protein expression by MSI2 at post transcriptional level. NSCLC lung tissue microarray immunohistochemistry analysis revealed that MSI2 total positivity by H-score, 2+/3+ and 3+ positivity correlated with EGFR 3+ staining. Finally, EGFR inhibitors erlotinib and afatinib synergized with MSI2 depletion in EGFR mutant models, suggesting that therapeutic targeting of MSI2 could be of clinical value, especially in EGFR-mutant lung cancer. In vivo experiments of erlotinib treatments of wild type or MSI2 depleted tumors are ongoing and these results will be presented.

Citation Format: Alexander Kudinov, Petr Makhov, Bulat Faezov, Igor Bychkov, Alexander Deneka, Emmanuelle Nicolas, Kathy Q Q. Caid, Rohan Brebione, Eleanor Avrilf, Anna S. Nikonova, Ilya G. Serebriiskii, Hossein Borghaei, Erica A. Golemis, Yanis Boumber. Musashi-2 regulates EGFR expression in NSCLC, cell proliferation and survival, response to EGFR inhibitors in EGFR-mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 955.

IL-27 Receptor Signaling potentiates Angiotensin II induced myelopoiesis and promotes Abdominal Aortic Aneurysm

Abdominal Aortic Aneurysm (AAA) is a vascular disease, where aortic wall degradation is in part mediated by the accumulation of immune cells leading to aortic wall rupture and bleeding which is often fatal for the patient. Smoking, age, male gender, hypertension and atherosclerosis are major risk factors, however the mechanism of AAA development is still elusive. Though cytokines regulate the inflammatory milieu within the aortic wall, their possible role in systemic regulation of this disease, particularly in the control of hematopoietic stem cell proliferation, myeloid cell differentiation and their subsequent accumulation in AAA remains poorly defined.

Here we report an unexpected pathogenic role of IL-27R signaling in the development of AAA. We found that in an animal model of AAA, prolonged infusion of Angiotensin (Ang) II robustly induces AAA formation in hyperlipidemic Apoe−/− and Apoe−/−Il27ra+/− mice but not in IL-27R deficient Apoe−/− mice. This mitigation of AAA formation in Apoe−/−Il27ra−/− mice is associated with a blunted accumulation of myeloid cells in suprarenal aortas due to a reduction of Ang II-induced hematopoietic stem and progenitor cell (HSPCs) expansion. We found that the absence of IL-27R signaling engages transcriptional programs that promote HSCs self-renewal program and suppress myeloid lineage differentiation, resulting in decreased mature myeloid cell production and thus a concomitant lack of Ang II-induced myeloid cell accumulation in the suprarenal aortas.

Collectively, these data demonstrate that IL-27R signaling influences AAA development by potentiating Ang II induced myelopoiesis and may represent a molecular point of therapeutic intervention in AAA.

Unexpected Activities in Regulating Ciliation Contribute to Off-target Effects of Targeted Drugs

PURPOSE

For many tumors, signaling exchanges between cancer cells and other cells in their microenvironment influence overall tumor signaling. Some of these exchanges depend on expression of the primary cilium on nontransformed cell populations, as extracellular ligands including Sonic Hedgehog (SHH), PDGFRα, and others function through receptors spatially localized to cilia. Cell ciliation is regulated by proteins that are themselves therapeutic targets. We investigated whether kinase inhibitors of clinical interest influence ciliation and signaling by proteins with ciliary receptors in cancer and other cilia-relevant disorders, such as polycystic kidney disease (PKD).

EXPERIMENTAL DESIGN

We screened a library of clinical and preclinical kinase inhibitors, identifying drugs that either prevented or induced ciliary disassembly. Specific bioactive protein targets of the drugs were identified by mRNA depletion. Mechanism of action was defined, and activity of select compounds investigated.

RESULTS

We identified multiple kinase inhibitors not previously linked to control of ciliation, including sunitinib, erlotinib, and an inhibitor of the innate immune pathway kinase, IRAK4. For all compounds, activity was mediated through regulation of Aurora-A (AURKA) activity. Drugs targeting cilia influenced proximal cellular responses to SHH and PDGFRα. In vivo, sunitinib durably limited ciliation and cilia-related biological activities in renal cells, renal carcinoma cells, and PKD cysts. Extended analysis of IRAK4 defined a subset of innate immune signaling effectors potently affecting ciliation.

CONCLUSIONS

These results suggest a paradigm by which targeted drugs may have unexpected off-target effects in heterogeneous cell populations in vivo via control of a physical platform for receipt of extracellular ligands.

Abstract 112: IL-27 Receptor Signaling Potentiates Angiotensin II Induced Myelopoiesis and Promotes Abdominal Aortic Aneurysm

Abdominal Aortic Aneurysm (AAA) is a vascular disease, where aortic wall degradation is mediated by accumulated immune cells. Several cytokines have been suggested to play role in AAA, however the role of cytokines in immune cell accumulation and AAA progression remains poorly defined. Here we report an unexpected role of IL-27R signaling in the development of AAA. We found that in an animal model of AAA, prolonged infusion of Angiotensin (Ang) II robustly induced AAA formation in hyperlipidemic Apoe -/- and Apoe -/- Il27ra +/- mice but failed to do so in Apoe -/- Il27ra -/- mice. This mitigation of AAA formation in Apoe -/- Il27ra -/- mice was associated with a blunted accumulation of pathogenic myeloid cells in suprarenal aortas resulting from a reduction in Ang II-induced hematopoietic stem and progenitor cell (HSPCs) expansion. We found that in the absence of IL-27R signaling HSPCs were unable to fully downregulate p21 expression in response to Ang II, which impeded the ability of Apoe -/- Il27ra -/- HSPCs to proliferate. Collectively, these data demonstrate that IL-27R signaling influences AAA development by activating emergency hematopoiesis in response to elevated Ang II. Further, they provide new insights into how the immunoregulatory cytokine IL-27 drives a prominent lethal vascular disease by distant regulation of stress/emergency hematopoiesis.

Abstract LB-320: Reconstituting B55/protein phosphatase 2A activity in B55/PP2A-defective prostate cancer cells suppresses proliferation and tumorigenicity through pleiotropic mechanisms

Prostate cancer accounts for close to 30,000 deaths annually in the United States. The most frequent alteration in the prostate oncogenome landscape is loss of chromosome 8p, which is also observed in other epithelial tumors. This region harbors NKX3.1, a prostate specific tumor suppressor, but 8p copy number loss does not correlate with its mRNA expression. The PPP2R2A gene, which encodes a regulatory subunit of protein phosphatase 2 (PP2A) designated B55, is located in 8p21.2 and is hemizygously lost in more that 50% of prostate adenocarcinomas. TCGA data analysis shows that hemizygous loss of PPP2R2A correlates with its reduced expression, poorer prognosis and that loss of PPP2R2A increases with metastasis to more than 80%. Of note, while homozygous loss is less common (4-10%), deletion of other subunits of the B55, but not other PP2A regulatory families, increases dramatically with metastasis despite their independent chromosomal locations. However, functional evidence that PPP2R2A acts as an haploinsufficient tumor suppressor and the potential mechanisms implicated are lacking. We have identified prostate cancer (PrCa) cell lines with reduced expression of B55 and shown that reconstitution of B55 expression reduces proliferation and induces senescence and loss of viability. B55 reconstitution in PC3 cells, an AR-negative model of human castration-resistant prostate cancer (CRPC), also blocks transformation in vitro and tumorigenicity in SCID mice. Reconstitution of B55 in PCa cells with reduced expression (PC3 and DU145 cells) induces cell cycle defects in G1, G2/M and mitosis diminishing and delaying phosphorylation of pRB pocket proteins and mitotic substrates and altering associated kinase networks. Mitogenic signaling is also attenuated. Importantly, the effects of B55 reconstitution are at least partially mimicked via treatment of these cells with PP2A activating drugs, which have anti-tumorigenic activity, indicating that development of specific B55/PP2A activating drugs targeting the unaltered B55 alleles remaining in PCa cells may have therapeutic potential for a high proportion of prostate tumors and perhaps other epithelial tumors such as luminal B breast and ovarian cancers which share this alteration.

Citation Format: Ziran Zhao, Alison Kurimchak, Petr Makhov, Katherine Johnson, Vladimir Kolenko, James Duncan, Xavier Graña. Reconstituting B55/protein phosphatase 2A activity in B55/PP2A-defective prostate cancer cells suppresses proliferation and tumorigenicity through pleiotropic mechanisms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-320. doi:10.1158/1538-7445.AM2017-LB-320

Abstract 668: The Role of IL-27 Receptor Signaling in the Development of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a cardiovascular disease, which is characterized by aortic wall dilation with subsequent rupture and internal bleeding. Inflammatory reactions in the vessel wall are likely essential for AAA pathogenesis, just like they are important for the development of another vascular pathology- atherosclerosis, which can predispose to AAA formation in a context-dependent manner. While inflammatory cytokines were shown to promote atherosclerosis and AAA, little is known about contribution of anti-inflammatory cytokines with regard to their ability to control vascular inflammation. Interleukin (IL)-27 signaling is required to suppress atherosclerosis development but its function in AAA remains unknown.

We utilize Angiotensin II (AngII) model to evaluate the role of IL-27R signaling in pathogenesis of AAA. AngII containing pumps were surgically implanted into Il27ra-/- x Ldlr-/-; Il27ra -/- x Apoe-/- and Il27ra+/- littermate controls and AAA progression was analyzed 4 weeks later.

Surprisingly, we found attenuated AAA progression in Il27ra-/- mice compared to Il27ra+/- and wt counterparts. The latter developed large AAA with visual hemorrhage into the artery wall, while Il27ra-/- mice developed small AAA with fewer myeloid cells and T cells. Moreover, opposite to aortic arches, T cells in abdominal aortas of Il27ra-/- mice produced less inflammatory IL-17A, while IFNγ production was unchanged. Interestingly, we found enhanced production of “Th2-like” cytokines IL-4 and IL-13, by NK cells and Type 2 Innate lymphoid cells (ILC2) in Il27ra deficient mice, which correlated with the protection from AAA.

Overall, we conclude that immunoregulatory cytokine IL-27 can differentially control atherosclerosis and AAA development by regulating innate and adaptive immune cell recruitment and cytokine production in the aortic wall.

Piperlongumine promotes autophagy via inhibition of Akt/mTOR signalling and mediates cancer cell death

BACKGROUND

The Akt/mammalian target of rapamycin (mTOR) signalling pathway serves as a critical regulator of cellular growth, proliferation and survival. Akt aberrant activation has been implicated in carcinogenesis and anticancer therapy resistance. Piperlongumine (PL), a natural alkaloid present in the fruit of the Long pepper, is known to exhibit notable anticancer effects. Here we investigate the impact of PL on Akt/mTOR signalling.

METHODS

We examined Akt/mTOR signalling in cancer cells of various origins including prostate, kidney and breast after PL treatment. Furthermore, cell viability after concomitant treatment with PL and the autophagy inhibitor, Chloroquine (CQ) was assessed. We then examined the efficacy of in vivo combination treatment using a mouse xenograft tumour model.

RESULTS

We demonstrate for the first time that PL effectively inhibits phosphorylation of Akt target proteins in all tested cells. Furthermore, the downregulation of Akt downstream signalling resulted in decrease of mTORC1 activity and autophagy stimulation. Using the autophagy inhibitor, CQ, the level of PL-induced cellular death was significantly increased. Moreover, concomitant treatment with PL and CQ demonstrated notable antitumour effect in a xenograft mouse model.

CONCLUSIONS

Our data provide novel therapeutic opportunities to mediate cancer cellular death using PL. As such, PL may afford a novel paradigm for both prevention and treatment of malignancy.

Are all multi-targeted tyrosine kinase inhibitors created equal? An in vitro study of sunitinib and pazopanib in renal cell carcinoma cell lines

OBJECTIVES

We examined the in vitro cellular effects of the multi-targeted receptor tyrosine kinase inhibitors (TKIs) sunitinib and pazopanib on a series of human renal cell carcinoma (RCC) cell lines.

METHODS

The human RCC cell lines 769-P, 786-O, HRC-24, HRC-31, HRC-45, HRC-78, SK-26B, and SK-45 were treated with varying concentrations of sunitinib and pazopanib. Cellular proliferation and cellular death were assessed using the CellTiter-Blue Cell Viability Assay and the TUNEL assay, respectively. Effective doses (ED) for inhibition of cellular proliferation or induction of apoptosis were calculated for sunitinib and pazopanib in each RCC cell line.

RESULTS

Both sunitinib and pazopanib exhibited anti-proliferative activity to varying degree against all human RCC cell lines; however, sunitinib's effects were achieved at significantly lower concentrations. Moreover, sunitinib had a direct pro-apoptotic effect on all tested cell lines, while pazopanib failed to induce apoptosis in any of the examined human RCC cell lines even at maximal concentrations.

CONCLUSIONS

Although sunitinib and pazopanib are often used interchangeably in the clinical setting, our results suggest that in-vitro biological activity of the two agents differs. Sunitinib exhibits a cytotoxic effect on RCC cell lines, while pazopanib's activity is solely cytostatic. These data may be clinically relevant given the current lack of comparative in-vivo studies between the two agents.