Jeremy D. Ward

LPA-mediated migration of ovarian cancer cells involves translocalization of Gαi2 to invadopodia and association with Src and β-pix

Lysophosphatidic acid (LPA) plays a critical role in the migration and invasion of ovarian cancer cells. However, the downstream spatiotemporal signaling events involving specific G protein(s) underlying this process are largely unknown. In this report, we demonstrate that LPA signaling causes the translocation of Gαi2 into the invadopodia leading to its interaction with the tyrosine kinase Src and the Rac/CDC42-specific guanine nucleotide exchange factor, β-pix. Our results establish that Gαi2 activates Rac1 through a p130Cas-dependent pathway in ovarian cancer cells. Moreover, our report reveals that knockdown of Gαi2 leads to loss of β-pix and active-Rac association in the invadopodia. We also show that knockdown of Gαi2 leads to the complete loss of translocation to p130Cas to focal adhesions. Finally, when Gαi2 is knocked down, this led to the total distribution of Src being shifted primarily from invadopodia and the leading edge of the cells to the perinuclear region, suggesting that Src is inactive in the absence of Gαi2. Overall, our report provides tantalizing evidence that Gαi2 is a critical signaling component of a large signaling complex in the invadopodia that if disrupted could serve as an excellent target for therapy in ovarian and potentially other cancers.

LPA Stimulates the Phosphorylation of p130Cas via Gαi2 in Ovarian Cancer Cells

Ovarian cancer is the most deadly gynecological cancer, with previous studies implicating lysophosphatidic acid (LPA) in the progression of approximately 90% of all ovarian cancers. LPA potently stimulates the tyrosine phosphorylation of p130Cas, a scaffolding protein, which, upon phosphorylation, recruits an array of signaling molecules to promote tumor cell migration. Our work presented here identifies Gαi2 as the major G protein involved in tyrosine phosphorylation of p130Cas in a panel of ovarian cancer cells consisting of HeyA8, SKOV3, and OVCA429. Our results also indicate that the G12 family of G proteins that are also involved in LPA-mediated migration inhibits tyrosine phosphorylation of p130Cas. Using p130Cas siRNA, we demonstrate that p130Cas is a necessary downstream component of LPA Gαi2-induced migration and collagen-1 invasion of ovarian cancer cells. Considering the fact that LPA stimulates invasive migration through the coordination of multiple downstream signaling pathways, our current study identifies a separate unique signaling node involving p130Cas and Gαi2 in mediating LPA-mediated invasive migration of ovarian cancer cells.

The gep proto-oncogene Gα12 mediates LPA-stimulated activation of CREB in ovarian cancer cells.

Lysophosphatidic acid (LPA) plays a critical role in the pathophysiology of ovarian cancers. Previous studies have shown that LPA stimulates the proliferation of ovarian cancer cells via Gα12. The present study utilizing Protein/DNA array analyses of LPA-stimulated HeyA8 cells in which the expression of Gα12 was silenced, demonstrates for the first time that Gα12-dependent mitogenic signaling by LPA involves the atypical activation cAMP-response element binding protein (CREB). Results indicate that the robust activation of CREB by LPA is an early event that can be monitored by the phosphorylation of SER133 of CREB as early as 3min. The findings that the expression of the constitutively activated mutant of Gα12 stimulates CREB even in the absence of LPA in multiple ovarian cancer cell lines confirm the direct role of Gα12 in the activation of CREB. This is further substantiated by the observation that the silencing of Gα12 drastically attenuates LPA-stimulated phosphorylation of CREB. Our results also establish that LPA-Gα12-dependent activation of CREB is through a cAMP-independent, but Ras-ERK-dependent mechanism. More significantly, our findings indicate that the expression of the dominant negative S133A mutant of CREB leads to a reduction in LPA-stimulated proliferation of HeyA8 ovarian cancer cells. Thus, results presented here demonstrate for the first time that CREB is a critical signaling node in LPA-LPAR and Gα12/gep proto-oncogene stimulated oncogenic signaling in ovarian cancer cells.

LPA Induces Metabolic Reprogramming in Ovarian Cancer via a Pseudohypoxic Response

Although hypoxia has been shown to reprogram cancer cells toward glycolytic shift, the identity of extrinsic stimuli that induce metabolic reprogramming independent of hypoxia, especially in ovarian cancer, is largely unknown. In this study, we use patient-derived ovarian cancer cells and high-grade serous ovarian cancer cell lines to demonstrate that lysophosphatidic acid (LPA), a lipid growth factor and GPCR ligand whose levels are substantially increased in ovarian cancer patients, triggers glycolytic shift in ovarian cancer cells. Inhibition of the G protein α-subunit Gαi2 disrupted LPA-stimulated aerobic glycolysis. LPA stimulated a pseudohypoxic response via Rac-mediated activation of NADPH oxidase and generation of reactive oxygen species, resulting in activation of HIF1α. HIF1α in turn induced expression of glucose transporter-1 and the glycolytic enzyme hexokinase-2 (HKII). Treatment of mice bearing ovarian cancer xenografts with an HKII inhibitor, 3-bromopyruvate, attenuated tumor growth and conferred a concomitant survival advantage. These studies reveal a critical role for LPA in metabolic reprogramming of ovarian cancer cells and identify this node as a promising therapeutic target in ovarian cancer.Significance: These findings establish LPA as a potential therapeutic target in ovarian cancer, revealing its role in the activation of HIF1α-mediated metabolic reprogramming in this disease. Cancer Res; 78(8); 1923-34. ©2018 AACR.

Abstract 31: Metabolic reprogramming in ovarian cancer

Ovarian cancer is currently the most lethal gynecologic malignancy, with no new significant changes in treatment options for these patients in the last 30 years. Importantly, ovarian cancer patients have increased levels of lysophosphatidic acid (LPA), a bioactive phospholipid in ascites and serum that has been linked to driving oncogenesis and progression of ovarian cancer. Accumulating evidence has implicated Hypoxia-inducible factor-1α (HIF-1α) as a critical mediator of the glycolytic shift observed in cancer cells. However, the precise biological role of LPA in regulating HIF-1α-mediated glycolytic shift is largely unknown. Therefore, we were interested in examining the potential role of LPA in promoting metabolic reprogramming in ovarian cancer via HIF-1α signaling. In this study, we identified a novel mechanism by which LPA upregulates HIF-1α expression via Gαi2 (the gip2 oncogene) in human ovarian cancer cells. This study demonstrates that LPA induces a glycolytic shift via LPA-mediated activation of Gαi2, which causes a subsequent upregulation of HIF-1α in ovarian cancer cells. Additionally, we show that LPA-signaling via Gαi2 induces an increase in the expression of Hexokinase-2 (HK2) and Glucose transporter 1 (GLUT1), which are known targets of HIF-1α. We also demonstrate that LPA induces an increase in extracellular acidification rate (ECAR) in a dose dependent manner in both ovarian cancer cell lines and in patient-derived cells taken from the ascites fluid of ovarian cancer patients using an XFe96 analyzer. Furthermore, we found that inhibition of Rac signaling caused a reduction in LPA-induced ECAR, identifying Rac as a critical downstream component of Gαi2-medidated increase of ECAR. Moreover, using NAC, an inhibitor of redox signaling, we found that this caused a decrease in LPA-induced ECAR in SKOV3-ip cells, indicating that inhibition of redox signaling abolishes LPA-induced ECAR in ovarian cancer cells. Similarly, the use of EUK-134, a scavenger of superoxide and H2O2, also decreased LPA-induced increase in ECAR. Altogether, these results indicate that LPA regulates glycolysis through redox signaling via a Gαi2-Rac-HIF1α-dependent signaling pathway. Most importantly, the Gαi2-Rac-dependent pathway identified in this study more than likely serves as a potential driver of HIF-1α-mediated metabolic changes in ovarian cancer cells and represents a potential target for therapy in these patients. Citation Format: JI HEE HA, Rangasudhagar Radhakrishnan, Jeremy D. Ward, Muralidharan Jayaraman, Danny N. Dhanasekaran. Metabolic reprogramming in ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 31.

Abstract 1057: LPA stimulates EMT of ovarian cancer cells via gip2 and gep oncogenes

Ovarian cancer is currently the most fatal gynecological cancer with a 5-year survival rate of only 45%. Recent studies have identified a critical role for lysophosphatidic acid (LPA) in the genesis and the progression of ovarian cancer. In order to identify transcription factors that are induced by LPA, a commercial pathway reporter array was used. Hypoxia induced factor 1 (HIF-1α) induction was the most prominent response showing more than 150 fold transcriptional activation compared with control. LPA treatment under normoxic and hypoxic (1% O2) conditions increased HIF-1α protein level, which leads to epithelial-to-mesenchymal transition (EMT) in the ovarian cancer cell line OVCA432. We also found that stimulation of the OVCA432 cells with LPA at normoxic and hypoxic conditions led to a significant increase of the mRNA and protein expression of the EMT transcription factor Twist. Immunofluorescent imaging confirmed that Twist levels were significantly up-regulated and that Twist was translocated to the nucleus as early as 4 hours after stimulation with LPA in both a normoxic and hypoxic environment. Additionally, immunofluorescent imaging showed that expression of E-cadherin on the periphery of the cell as well as in the whole cell was greatly reduced when cells were stimulated with LPA in normoxic and hypoxic conditions. Finally, our study demonstrated that LPA-mediated induction of EMT required both gip2 and gep oncogenes. Overall, our study indicated that the downstream components regulated by oncogenic G-proteins could potentially be targeted in the future to prevent EMT in ovarian cancer. Citation Format: Ji Hee Ha, Jeremy Ward, Danny N. Dhanasekaran. LPA stimulates EMT of ovarian cancer cells via gip2 and gep oncogenes. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1057. doi:10.1158/1538-7445.AM2014-1057

Abstract 3020: The gep protooncogene Gα12 mediates LPA-stimulated activation of CREB in ovarian cancer cells.

Lysophosphatidic acid (LPA), plays a critical role in the pathophysiology of ovarian cancers. Our previous studies have shown that LPA stimulates the proliferation of ovarian cancer cells through GNA12, the gep protooncogene Gα12. The present study is focused on identifying the Gα12-dependent mechanism through which LPA stimulates the proliferation of ovarian cancer cells. Using ovarian cancer cells in which the expression of Gα12 is silenced, we demonstrate here that Gα12-dependent mitogenic signaling by LPA involves the atypical activation of the transcription factor, cAMP-response element binding protein (CREB). Protein/DNA array analyses using LPA-stimulated Hey8 cells in which the expression of Gα12 was silenced indicated the potent but Gα12-dependent activation of CREB by LPA. After validating the array data with immunoblot analysis using antibodies specific to Ser133-phosphorylated active form of CREB, we demonstrate that the expression of the constitutively activated mutant of Gα12 stimulate the activation of CREB even in the absence of LPA whereas silencing of Gα12 abrogates such LPA-stimulated activation in multiple ovarian cancer cell lines. Furthermore, our results indicate that the robust activation of CREB by LPA is an early event, which can be monitored upon LPA stimulation from 3 minutes onwards. In addition, we establish that LPA/Gα12-dependent activation of CREB involves an atypical cAMP-independent mechanism involving Ras and ERK. More significantly, our findings indicate that the expression of the dominant negative mutant of CREB (S133A) leads to a reduction in LPA-stimulated increase in Cyclin A levels along with an attenuation of LPA-stimulated proliferation of these cells. Thus, these studies unravel a novel Gα12-dependent mechanism involving CREB through which LPA stimulates the proliferation of ovarian cancer cells. Citation Format: Ji Hee Ha, Danny Dhanasekaran, Jeremy Ward, Yoon Mi Yang, Sang Geon Kim, Lakshmi Varadarajalu. The gep protooncogene Gα12 mediates LPA-stimulated activation of CREB in ovarian cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3020. doi:10.1158/1538-7445.AM2013-3020

Abstract LB-24: LPA-mediated oncogenic signaling in ovarian cancer involves p130Cas

Ovarian cancer is the most deadly gynecological cancer and the need for new therapies is evidenced by the fact no new drugs targeting ovarian cancer have been identified. Recent studies have shown that lysophosphatidic acid (LPA), a lipid growth factor, is implicated in the genesis and progression of ovarian cancer, yet the majority of the mechanisms through which LPA promotes cancer genesis and progression remain to be elucidated. Therefore, the underlying theme of our research is to identify novel LPA-activated signaling nodes that can be targeted for therapy in ovarian cancer. Subjecting the lysates from HeyA8 ovarian cancer cells to a high-throughput antibody array analysis, we identified that LPA potently stimulates the tyrosine-phosphorylation of p130Cas, a scaffolding protein, which, upon phosphorylation, recruits an array of signaling molecules that promotes tumor cell proliferation, survival and metastasis. The antibody-array data was validated via immunoprecipitation of p130Cas and immunoblotting with a phospho-tyrosine specific antibody in a panel of ovarian cancer cells consisting of HeyA8, OVCA429, OVCA432 and SKOV3, establishing cell-type independent activation of p130Cas by LPA. Analyzing further, we have identified that tyrosine-410 of p130Cas is phosphorylated in response to LPA. Several past studies, including ours, have shown oncogenic signaling by LPA involves the activation of LPA receptors that are coupled to the α-subunits of the heterotrimeric G proteins, Gi, Gq, G12, and/or G13. To define the specific α-subunit that mediates LPA-induced p130Cas-phosphorylation, we monitored Tyr-410 phosphorylation of p130Cas in response to 20 μM of LPA (20 min) in HeyA8 cells in which the expression of Gαi2, Gαq, Gα12, or Gα13 was silenced by specific shRNAs. Our results indicated that only the silencing of Gαi2 abrogated LPA-mediated Tyr-410 phosphorylation of p130Cas. Since Gαi2 has been shown to play a critical role in LPA-LPAR coupled cell migration, we hypothesized that the LPA-LPAR-Gαi2-p130Cas signaling axis is involved in the invasive migration of ovarian cancer cells. To test this hypothesis, we examined whether the knocking down of p130Cas, via p130Cas-specific siRNA, attenuated LPA-mediated migration of ovarian cancer cells. Our results indicated that the silencing of p130Cas significantly inhibited LPA-stimulated migration of ovarian cancer cells by 58%. Thus, our study is the first to establish LPA-LPAR-Gαi2-mediated stimulation of p130Cas is involved in invasive migration of ovarian cancer cells. Overall, the results presented in our current study point to p130Cas as a critical signaling node in pathological LPA signaling and that by targeting LPA receptors, LPA production and/or the downstream kinases that phosphorylate p130Cas, it may be possible to disable the oncogenic signaling cascades activated by p130Cas in ovarian cancer and enhance the survival of ovarian cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-24. doi:1538-7445.AM2012-LB-24