Abstract 1854: Evidence that RARs interact with Src family kinases and that inhibition of Src family kinase activity can affect the growth response of SKOV3 ovarian cancer cell to atRA

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Chemotherapy resistance is a major cause of ovarian cancer treatment failure. All trans-retinoic acid (atRA) is a promising therapeutic agent due to its growth suppressing activity however, not all ovarian carcinomas are growth inhibited by atRA. Understanding the underlying mechanisms of atRA action in ovarian cancer is crucial to overcome chemotherapy resistance. Recent studies have reported novel nongenomic actions of atRA and retinoic acid receptors (RARs). The main goal of this work was to study nongenomic actions of RARs. A SH3 domain phage display was performed to identify proteins that interact with the proline rich region of RARγ. Our results indicated that RARγ proline rich region binds to the SH3 domain of Src family kinase proteins (SFKs) Lyn, Src and Yes. Immunofluorescence assays showed that RARγ colocalizes in the cell cytoplasm with Lyn, Src and Yes. Proximity ligation assays were performed to determine whether RARs and Lyn, Src and Yes interact in vivo. Our results showed that RARα and RARγ but not RARβ form a complex with both Lyn and Src. No interaction was found between any of the RARs and Yes. Interaction between RARs and SFKs was found to be directly correlated with phosphorylation of Y419 in Src and Y397 in Lyn. We have previously shown that the ovarian cancer cell line CAOV3 is sensitive to growth inhibition by atRA while the ovarian cancer cell line SKOV3 is resistance to atRA growth repression. Since SFKs such as Src and Lyn are known to regulate cancer cell growth, we next investigated the effect of inhibiting SFKs activity on the atRA regulated growth response of these cell lines. CAOV3 and SKOV3 cells were treated with atRA (1μM) alone or in combination with varying doses of SFKs inhibitors PP1 and PP2 and analyzed for cell growth inhibition. CAOV3 but not SKOV3 cells were growth arrested by atRA. Both PP1 and PP2 caused growth inhibition in both cell lines. Interestingly, when atRA was combined with either of the SFKs inhibitors, SKOV3 but not CAOV3 cells exhibited growth inhibition greater than that observed with PP1 or PP2 alone. These data demonstrate that inhibition of SFKs activity converts the growth response of SKOV3 cells from atRA resistant to atRA sensitive. Analysis of cell cycle regulators in atRA and PP1 treated CAOV3 cells showed that both p27 and p130 are up-regulated while CDK6 is down-regulated. On the other hand, in SKOV3 cells treated with atRA and PP1, p130 is unaffected while p27, cyclin A, CDK1, CDK2 and CDK6 are down-regulated. In conclusion, we have confirmed the interaction between RARγ and Src and describe for the first time the interaction between RARα and both Lyn and Src, and RARγ and Lyn. We also provide evidence that reduction of SFKs activity and atRA treatment but not atRA treatment alone can inhibit the growth of SKOV3 cells. This suggests that SFKs activity must be reduced in order for atRA to inhibit cell growth in at least some ovarian carcinomas. Citation Format: Thais Acquafreda Lakind, Kenneth Soprano, Dianne Soprano. Evidence that RARs interact with Src family kinases and that inhibition of Src family kinase activity can affect the growth response of SKOV3 ovarian cancer cell to atRA. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1854. doi:10.1158/1538-7445.AM2015-1854