Nuclear α1-Antichymotrypsin Promotes Chromatin Condensation and Inhibits Proliferation of Human Hepatocellular Carcinoma Cells

BACKGROUND & AIMS: alpha 1-Antichymotrypsin (alpha 1-ACT), a member of the serpin family (SERPINA3), is an acute-phase protein secreted by hepatocytes in response to cytokines such as oncostatin M. alpha 1-ACT is a protease inhibitor thought to limit tissue damage produced by excessive inflammation-associated proteolysis. However, alpha 1-ACT also is detected in the nuclei of cells, where its activities are unknown. Expression of alpha 1-ACT is down-regulated in human hepatocellular carcinoma (HCC) tissues and cells; we examined its roles in liver regeneration and HCC proliferation. METHODS: We measured levels of alpha 1-ACT messenger RNA in human HCC samples and healthy liver tissue. We reduced levels of alpha 1-ACT using targeted RNA interference in human HCC (HepG2) and mouse hepatocyte (AML12) cell lines, and overexpressed alpha 1-ACT from lentiviral vectors in Huh7 (HCC) cells and adeno-associated viral vectors in livers of mice. We assessed proliferation, differentiation, and chromatin compaction in cultured cells, and liver regeneration and tumor formation in mice. RESULTS: Reducing levels of alpha 1-ACT promoted proliferation of HCC cells in vitro. Oncostatin M up-regulated alpha 1-ACT expression and nuclear translocation, which inhibited HCC cell proliferation and activated differentiation of mouse hepatocytes. We identified amino acids required for alpha 1-ACT nuclear localization, and found that alpha 1-ACT inhibits cell-cycle progression and anchorage-independent proliferation of HCC cells. HCC cells that overexpressed alpha 1-ACT formed smaller tumors in mice than HCC cells that did not express the protein. alpha 1-ACT was observed to self-associate and polymerize in the nuclei of cells; nuclear alpha 1-ACT strongly bound chromatin to promote a condensed state that could prevent cell proliferation. CONCLUSIONS: alpha 1-ACT localizes to the nuclei of hepatic cells to control chromatin condensation and proliferation. Overexpression of alpha 1-ACT slows the growth of HCC xenograft tumors in nude mice.