Abstract PD15-05: Sipa1 effects rock pathway in human breast cancer linking to HGF mediated changes in tight junction functions controlling metastasis

Background: SIPA1 (Signal-induced proliferation-associated gene 1) is a mitogen-inducible gene encoding a GTPase-activating protein for Rap1 and Rap2 and has been suggested to be involved in metastatic progression. We have previously shown SIPA1 may regulate barrier function in breast cancer cells as part of hepatocyte growth factor-determined changes and that this may be via a number of regulatory pathways, most likely via the ROCK pathway. Our aim with this current work was to definitively identify which pathway is involved. Methods: After knockdown of SIPA1 in MDA-MB-231 cells, they were treated to a number of inhibitors to proteins involved in pathways involved in TJ barrier function (ROCK, N-WASP, ARPs, WAVEs, MAPK, ERK, PLC-gamma). Following the identification of suitable inhibitor a large scale in vivo study was carried out using a tumour model of SIPA1 knockdown versus WT control was treated with/without inhibitors and immunohistochemistry (IHC) used to assess changes in tumour growth, architecture and protein expression. We also assessed the expression of SIPA-1 in a cohort of human breast cancer tissues using IHC. Results: After knockdown of SIPA1 in MDA-MB-231 cells, we subjected cells to a number of inhibitors to proteins involved in pathways involved barrier function (ROCK, N-WASP, ARPs, WAVEs, MAPK, ERK, PLC-gamma). Analysis of behaviour showed that knockdown cells no longer responded to the ROCK inhibitor (ROCKi Y-27632, p Citation Format: Chang Liu, Fiona Ruge, Lin Ye, Gregory M. Harrison, Wen G. Jiang, Tracey A. Martin. Sipa1 effects rock pathway in human breast cancer linking to HGF mediated changes in tight junction functions controlling metastasis [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD15-05.