Abstract 2805: LPA-dependent regulation of VCAM-1 in the ovarian cancer metastatic microenvironment and its impact on mesothelial invasion.
Authors: Raines Timothy A. , Lynch Kevin R. , Slack-Davis Jill K. 
Published: August 2014

Ovarian cancer is the leading cause of gynecological cancer deaths in the United States due in large part to the advanced stage of disease at diagnosis. The poor prognosis is attributed to ovarian cancer metastasis to the peritoneal cavity and the accumulation of ascites, which contains elevated levels of several growth factors and cytokines including lysophosphatidic acid (LPA), a bioactive lipid that promotes ovarian cancer proliferation and survival as well as activities relevant to metastasis including migration and invasion. Ovarian cancer metastasis is a complex process that involves attachment to and invasion through the mesothelium and has been associated with vascular cell adhesion molecule 1 (VCAM-1). Previously we have shown that VCAM-1 is preferentially expressed on the mesothelium of patients with ovarian cancer where it functions to promote mesothelial invasion. Inhibition of VCAM-1 function reduces tumor burden and increases survival in a mouse model, implicating VCAM-1 as an important target for the treatment of ovarian cancer. Since LPA promotes ovarian cancer migration and invasion, we questioned whether it also influenced the mesothelium to regulate invasion. Using a co-culture system to measure ovarian cancer cell invasion of the mesothelium, treatment with a VPC51299, a LPA1/3 receptor antagonist, which targets both the cancer cells and the mesothelium, resulted a dose dependent decrease in mesothelial invasion. Importantly, specific targeting of the mesothelium using siRNA directed at the LPA1 receptor also diminished ovarian cancer cell invasion of the mesothelium. Additionally, we observed that siRNA knockdown of the LPA receptor diminished VCAM-1 expression; re-expression of VCAM-1 to endogenous levels in cells lacking LPA receptor expression restored mesothelial invasion. To determine how LPA regulated VCAM-1 expression, human mesothelial cells derived from ovarian cancer patients (LP9 or LP3) were subjected to siRNA inhibition of LPA1 receptor expression and protein and mRNA expression were evaluated. The results revealed a significant decrease in VCAM-1 protein expression but no impact on VCAM-1 mRNA levels, indicating that LPA does not have a major role in the regulation of VCAM-1 transcription as has been reported in other systems. Rather, it implicates LPA in the regulation of VCAM-1 protein expression. To investigate whether LPA regulates VCAM-1 protein stability, LP9 cells were treated with a eukaryotic translation inhibitor, cycloheximide, for increasing periods of time. VCAM-1 protein half-life decreased after treatment with cycloheximide and LPA1 knockdown compared to control. Taken together, these observations indicate that in addition to targeting the cancer cells, LPA influences the tumor microenvironment to promote mesothelial invasion in part by regulating VCAM-1 protein stability.

Citation Format: Timothy A. Raines, Kevin R. Lynch, Jill K. Slack-Davis. LPA-dependent regulation of VCAM-1 in the ovarian cancer metastatic microenvironment and its impact on mesothelial invasion. [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 2805. doi:10.1158/1538-7445.AM2013-2805