Abstract 288: Loss of a branched actin checkpoint in cancer cells

Abstract

Abstract Cell proliferation depends on multiple signals, such as growth factors, adhesion to the substratum and to neighboring cells. Cancer cells proliferate independently of these signals. The same stimuli also induce actin polymerization. Here we investigate whether the actin cytoskeleton plays a role in transmitting the proliferation signal. We found that inactivation of the Arp2/3 complex by either a chemical inhibitor or by siRNAs blocks S phase entry in untransformed human breast cell lines and in primary breast epithelial cells. In contrast, breast cancer cell lines did not respond to Arp2/3 inhibition. Inactivating the tumor suppressor p21WAF1/CIP1, or Rb, converts sensitive cells into unresponsive cells further highlighting that this response to Arp2/3 inactivation is at the heart of the transformation process. The depletion of the WAVE complex, the Arp2/3 activator that generates branched actin in lamellipodia, but not of other Arp2/3 activators, blocks cell cycle progression. Conversely, activation of WAVE by active Rac, or depletion of Arpin, which antagonizes WAVE, potentiates cell cycle progression. Together, these results show that branched actin networks generated in lamellipodia are sensed and convey an essential signal for S Phase entry. The signal that branched actin delivers integrates stimulation from soluble growth factor with mechanotransduction from cell adhesions to the substratum and to neighboring cells. This signaling pathway qualifies as a checkpoint, which is required in normal cells, but lost in transformed cells, that monitors the integrity of branched actin networks and instructs the cell as a response that the required conditions to proliferate are fulfilled. Citation Format: Nicolas Molinie, Svetlana Rubtsova, Alexis Gautreau. Loss of a branched actin checkpoint in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 288. doi:10.1158/1538-7445.AM2017-288