Differential expression of smooth muscle alpha-like actin between benign and malignant human pigment tissues

When examining proteins in human pigment tissues, we found that a third actin-like protein, in addition to beta- and gamma-actin was more frequent and in a larger amount in benign tissues such as blue nevus and nevus pigmentosus, than in malignant melanoma. This third actin-like protein was immunologically stained with monoclonal antibodies reacting with several actin species and specific for smooth muscle alpha-actin. We propose that this third actin-like protein is probably smooth muscle alpha-actin and that different expressions of this third actin may possibly serve as a sensitive biochemical marker for the diagnosis of human malignant melanoma.