Kappa-Actin Alters Hepatocellular Carcinoma Physiology in Cirrhotic Microenvironment

Abstract

Hepatocellular carcinoma (HCC) is the fifth most common cause of cancer-related mortality over the world, and liver cirrhosis was reported as the most important risk factor for HCC development. However, the roles of mechanotransduction in HCC have not been fully explored yet. Kappa-actin (κ-actin), a novel class of actin correlated with poor postoperative survival, was selected as our study model. We investigated how κ-actins regulate HCC cells using stiffness adjustable polymeric matrixes, which mimic the cirrhotic microenvironment. Different cellular physiology, such as proliferation, contact topography and 3-dimensional invasion, were observed in microenvironment with different stiffness. Interestingly, with high k-actin expression, we noticed the significantly decrease of focal adhesions (FAs) formation while substrate's stiffness > 16 kPa. Photoactive microscopy showed lower stability of k-actin structures, and the unstable actin organization can contribute to the decrease of FAs/Adherence junction (AJs) formations. Furthermore, the instability of AJs (E-cadherin) may correlate to the observed higher invasion of k-HCC in vitro. Traction force microscopy (TFM) was developed to further quantify the mechanical interactions at the ECM-cell/cell-cell interfaces. By measuring the deformation of polymeric gel substrates, the force balance at the contact surfaces can be reconstructed. We observed the ECM-cell traction force increased with the increasing substrate stiffness, and the traction force decreased with the k-actin expression, which consisted with the spatial pattern of FAs. In summary, we showed the expression of k-actin alters the formation of FAs/AJs in HCC, which can contribute to the observed high cell proliferation and invasion of HCC. Furthermore, using photoactive microscopy, we demonstrated the actin dynamics play the essential roles in FAs and AJs formation of HCC. These findings may contribute to our understanding about the influence of actins on HCC through mechanotransduction perspective.