Abstract 2635: ROR1-CAVIN3 interaction required for caveolae-dependent endocytosis and pro-survival signaling in lung adenocarcinoma

Abstract

Abstract TTF-1/NKX2-1, a homeobox-containing transcription factor indispensable for lung morphogenesis, was previously identified by four independent groups including us, as a “lineage-survival” oncogene involved in the pathogenesis of lung adenocarcinoma. We have further shown that TTF-1 induces expression of the receptor tyrosine kinase-like orphan receptor 1 (ROR1), which in turn sustains a favorable balance between pro-survival PI3K-AKT and pro-apoptotic ASK1-p38 signaling in both ROR1 kinase activity-dependent and -independent manner. It is interesting to note that while alterations in EGFR signaling are involved as a “driver” in lung adenocarcinoma pathogenesis, ROR1 appears to play a “sustainer role” for the EGFR-mediated signaling. Previously, we have also found an unanticipated function of this ROR1 receptor tyrosine kinase (RTK) as a scaffold of CAVIN1 and caveolin-1 (CAV1), two essential structural components of caveolae. This kinase-independent function of ROR1 facilitates the interactions of CAVIN1 and CAV1 at the plasma membrane, thereby preventing the lysosomal degradation of CAV1. Caveolae structures and pro-survival signaling towards AKT through multiple RTKs, including EGFR, MET, and IGF-IR are consequently sustained. Therefore, ROR1 is an attractive target for overcoming EGFT-TKI resistance due to various mechanisms such as EGFR T790M double mutation and bypass signaling from other RTKs. Caveolae function in vesicular and cholesterol trafficking, and have roles in internalization of cholera toxins and the SV40 virus, as well as glycosylphosphatidylinositol (GPI)-anchored proteins and various RTKs. Endocytosis supports various cellular functions, such as nutrient uptake, intracellular signaling, morphogenesis, and defense against pathogens, and is tightly regulated, while it also ensures an appropriate amplitude of growth factor signaling by recycling RTKs back to the cell surface or sorting them to lysosomes for degradation. Here we report that ROR1 possesses a novel scaffold function indispensable for efficient caveolae-dependent endocytosis. CAVIN3 was found to bind with ROR1 at a site distinct from sites for CAV1 and CAVIN1, a novel function required for proper CAVIN3 subcellular localization and caveolae-dependent endocytosis, but not caveolae formation itself. Furthermore, evidence of a mechanistic link between ROR1-CAVIN3 interaction and consequential caveolae trafficking, which was found to utilize a binding site distinct from those for ROR1 interactions with CAV1 and CAVIN1, with RTK-mediated pro-survival signaling towards AKT in early endosomes in lung adenocarcinoma cells was also obtained. The present findings warrant future study to enable development of novel therapeutic strategies for inhibiting the multifaceted scaffold functions of ROR1 in order to reduce the intolerable death toll from this devastating cancer. Citation Format: Tomoya Yamaguchi, Miyu Hayashi, Lisa Ida, Masatoshi Yamamoto, Can Lu, Taisuke Kajino, Jinglei Cheng, Masahiro Nakatochi, Hisanori Isomura, Motoshi Suzuki, Toyoshi Fujimoto, Takashi Takahashi. ROR1-CAVIN3 interaction required for caveolae-dependent endocytosis and pro-survival signaling in lung adenocarcinoma [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 2635.