Identification of a novel actin isoform in hepatocellular carcinoma

Objective: Altered actin isoform expression occurs in some pathological conditions including muscular malignancies. This study was to investigate whether a similar event occurs in hepatocellular carcinoma. Methods: Cellular RNA was extracted from cancerous and non-cancerous hepatoma tissues. Reverse transcription (RT)-PCR followed by cloning and sequencing was performed to obtain populations of actin sequences. Phylogenetic analysis was carried out to identify novel actin isoforms. Interaction between the novel actin isoform and other cellular proteins was examined by the yeast two-hybrid system. The relative amounts of the novel actin isoform in the cancerous and non-cancerous tissues were further assayed using real-time PCR with specific primers. Results: When compared between the cancerous and non-cancerous tissues, the proportion of non-β-actins in the cancerous parts increased significantly in three of four cases included. Among the non-β-actins, a novel group of isoforms was identified, temporarily named κ-actins. Two genetically closely related sequences, FKSG30 and an actin-like sequence in the Cat Eye syndrome region, were found to cluster with the κ-actins. Protein interaction assay indicated that the interaction between κ-actin and prefoldin 2 was greatly diminished. The relative amounts of κ-actin increased in 12 of 20 cancerous tissues assayed. Conclusions: A novel class of actin isoforms was expressed in some hepatocellular carcinoma tissues, replacing β-actins to become the major constituents of actin cytoskeleton.