Abstract POSTER-BIOL-1301: The receptor tyrosine kinase AXL modulates oncogenic signaling and epithelial mesenchymal transition in epithelial ovarian cancer
Authors: Antony Jane , Tan Tuan Zea , Paterson Andrew , Recchi Chiara , Gabra Hani , Thiery Jean Paul , Huang Ruby Yun-Ju 
Published: August 2015

Metastasis in epithelial ovarian cancer (EOC) is lethal, and results into a 5-year-survival rate lower than 30%. In EOC, tumor cells undergo Epithelial-Mesenchymal Transition (EMT) to attain the invasive and migratory potential crucial for metastasis. The analysis of molecular heterogeneity in EOC also demonstrated the important role of EMT. Our group has previously classified EOC tumors and cell lines into 5 distinct molecular subtypes based on their global gene expression patterns. Among these subtypes, the Mesenchymal subtype is believed to be driven by EMT. Receptor Tyrosine Kinases (RTKs), which play a pivotal role in proliferation and survival pathways, have been strongly indicated to mediate signals in EMT. Upon interrogating the kinome expression patterns by determining the top 10 ranked kinases in each molecular subtype, the RTK AXL was revealed to have a significantly high ranking in the Mesenchymal subtype. The purpose of this study is to elucidate the role of AXL in oncogenic signaling and EMT in EOC.

Western Blotting of total Axl protein in a panel of 40 EOC cell lines revealed a distinctive pattern among the 5 molecular subtypes. Upon ligand activation by Gas6 in Axl-expressing cell lines, pERK and pAkt, two signaling molecules downstream of Axl, displayed a unique temporal signaling pattern specific to the Mesenchymal subtype. This resulted into an implication of the preferential sensitivity to Axl-specific inhibitors in the Mesenchymal subtype. The IC-50 of R428, one small molecule inhibitor specific to Axl, was significantly lower in the Mesenchymal cell lines compared to the other subtypes (Average of 2.91 μM versus 9.38 μM; p-value=0.01)

Stable clones were generated by using shRNAs to knockdown AXL in Mesenchymal EOC lines. shAXL SKOV3 cells demonstrated a reversal of EMT evident by restoration of Ecadherin. siRNA mediated transient silencing of AXL showed a reduction in cell motility with decreased total displacement and velocity measured over 12 hours (31.98 μm compared to 44.59 μm, p-value=0.01; and 17.35 μm/second compared to 23.15 μm/second, pvalue= 0.03) measured by using single cell tracking. Survival analysis showed that AXL over expression correlated positively with poor overall survival of EOC in both univariate (HR=2.2 p-value=6.46e−11), and multivariate analysis (HR=1.513 p-value=0.0012).

In conclusion, AXL is significantly over-expressed and displays a unique signaling pattern in the Mesenchymal subtype of EOC. Knocking down AXL in the Mesenchymal cell lines affects their EMT phenotype and migratory properties. AXL is an independent prognostic factor for EOC and is a clinically relevant target that is potentially involved in cross talks between RTK oncogenic signaling and EMT.

Citation Format: Jane Antony, Tuan Zea Tan, Andrew Paterson, Chiara Recchi, Hani Gabra, Jean Paul Thiery, Ruby Yun-Ju Huang. The receptor tyrosine kinase AXL modulates oncogenic signaling and epithelial mesenchymal transition in epithelial ovarian cancer [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1301.