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 γ-actin in non-muscle cells. In addition, anti-pan actin antibody recognized the purified 44-kDa protein, whereas anti-muscle actin and anti-β-actin antibodies did not. Thus, we concluded that the 44-kDa protein was non-muscle γ-actin. An immunohistochemical study revealed that the non-muscle γ-actin accumulated next to the plasma membrane of liver parenchymal cells during regeneration. Moreover, the γ-actin level was augmented in primary cultured rat hepatocytes prior to DNA synthesis. Intracellular γ-actin in cultured hepatocytes was distributed across the entire basal plane after stimulation with hepatocyte mitogens. This change in the distribution of γ-actin correlated with the cell spreading that occurred during the G1/S phase transition. These findings indicated that γ-actin plays specific roles in the growth of liver parenchymal cells during liver regeneration.