Targeting the cytoskeleton inhibits proliferation of hepatoma cells by suppressing mitogenic signalling

Abstract

Hepatocellular carcinoma (HCC) develops almost exclusively on a background of chronic liver inflammation and cirrhosis. We have shown before, that hepatoma cells are able to sense and respond to the increased stiffness of the cirrhotic liver leading to increased cellular tension, stress fibre formation and proliferation. The FAK-Rho/ROCK-MLC2/Myosin pathway has been identified in other tissues to be a central regulator of cellular responses to increased environmental stiffness.The aim of the study was to evaluate the relevance of the stiffness-sensing pathway in the regulation of the cytoskeleton and to test, whether targeting this pathway might influence proliferation and survival of hepatoma cells. Therefore small compound inhibitors for FAK, ROCK and Myosin were evaluated in the human hepatoma cell lines HepG2 and Huh7 cultured on standard plastic (stiff) cell culture plates.Inhibitors for ROCK and Myosin reduced cellular spreading in the hepatoma cells, leading to a rounded phenotype with reduced stress fibres. In contrast upon FAK inhibition the cells were still spread out and displayed stress fibres albeit less organized in comparison to non-inhibited cells. Inhibitor treated cells displayed a reduced proliferative index and a reduced cell number after 5 days of treatment compared to untreated control cells. Accordingly, there was a dose-dependent inhibition of mitogenic signalling through Erk and Stat3 by all inhibitors. Cell survival was decreased in inhibitor treated cells after incubation with the chemotherapeutic drug cisplatin in a synergistical manner. The increased induction of apoptosis by cisplatin in inhibitor treated cells was verified by showing enhanced PARP cleavage compared to non-inhibited cells.In conclusion, interfering with the mechano-sensing machinery in the tumour cells might prove to be a new therapeutic target in HCCs arising in a stiff cirrhotic liver.