SMP30 Interacts with ROCK1 to Inhibit HCC Invasiveness by Effecting the Epithelial-Mesenchymal Transition

Abstract

Background: The senescence marker protein 30 (SMP30) is a calcium-binding protein whose expression decreases with age, and is closely associated with hepatocellular carcinoma (HCC) development. The primary goal of this study was to examine the mechanistic effect of SMP30 on HCC migration and invasion. Methods: Bioinformatic and immunohistochemical approaches were used to examine the expression of SMP30 in HCC tissues and its relationship to patient survival. We investigated the effects of SMP30 expression on HCC cell proliferation, migration, invasion, and cell cycle dynamics. cDNA microarray technology was used to determine the gene expression profile of SK-Hep-1 cells following recombinant SMP30 overexpression to identify genes downstream of SMP30 that regulate HCC cell migration and invasion. We identified SMP30 interacting proteins by affinity purification-mass spectrometry (AP-MS) and co-immunoprecipitation/western blotting (COIP-WB). Results: SMP30 expression was lower in HCC tissues compared with normal liver tissues, and its expression positively correlated with overall survival in HCC patients. Additionally, SMP30 overexpression effectively blocked the migratory and invasive properties of SK-Hep-1 cells, but did not affect either proliferation rates or cell cycle. cDNA microarray results confirmed that many of the differentially expressed genes identified are involved in the process of epithelial-mesenchymal transition (EMT). AP-MS and COIP-WB experiments confirmed that Rho-associated protein kinase 1 (ROCK1) interacts with SMP30 in SK-Hep-1 cells, and ROCK1 is known to intimately regulate the EMT process. Conclusion: SMP30 inhibits HCC metastasis by influencing the expression of EMT-related proteins after interacting with ROCK1.

Keywords

• hepatocellular carcinoma
• senescence marker protein 30
• rho-associated protein kinase 1
• epithelial-mesenchymal transition