Enhancement of gamma-actin protein during liver regeneration: its accumulation in a region adjacent to the hepatocyte plasma membrane.

We identified a protein with a molecular weight of about 44 kDa in an extract of rat regenerating liver. This protein was undetectable in normal, sham-operated, and completely regenerated liver. We also purified this 44-kDa protein from an extract of rat liver remnant after partial hepatectomy. The partial amino acid sequences of the purified protein were identical to those of gamma-actin in non-muscle cells. In addition, anti-pan actin antibody recognized the purified 44-kDa protein, whereas anti-muscle actin and anti-beta-actin antibodies did not. Thus, we concluded that the 44-kDa protein was non-muscle gamma-actin. An immunohistochemical study revealed that the non-muscle gamma-actin accumulated next to the plasma membrane of liver parenchymal cells during regeneration. Moreover, the gamma-actin level was augmented in primary cultured rat hepatocytes prior to DNA synthesis. Intracellular gamma-actin in cultured hepatocytes was distributed across the entire basal plane after stimulation with hepatocyte mitogens. This change in the distribution of gamma-actin correlated with the cell spreading that occurred during the G1/S phase transition. These findings indicated that gamma-actin plays specific roles in the growth of liver parenchymal cells during liver regeneration.