Expression of a variant form of actin and additional polypeptide changes following chemical-induced in vitro neoplastic transformation of human fibroblasts.

Malignant human fibroblasts, transformed in vitro by a single chemical treatment, and the untransformed parental cells have been compared by two-dimensional gel electrophoresis of their proteins. One transformed cell line, HUT-14, exhibits an abundance of a new polypeptide, A' (pI 5.2; molecular weight 44,000), amounting to approximately 3% of the cellular protein. There are at least 23 additional differences in polypeptides out of greater than 1000 electrophoretically distinguishable species. The A' polypeptide has been identified as a variant form of actin by immunoprecipitation with anti-actin antibody and comparison of its tryptic peptide patterns with those produced by beta- and gamma-actin polypeptides also found in HUT-14 cells. A' is distinguishable from the normal forms of actin (alpha, beta, and gamma polypeptides) in that it is more acidic and migrates at a slower rate in sodium dodecyl sulfate gels. Synthesis of A' may occur as a result of a somatic mutation affecting one of the normal actin genes. The electrophoretic behavior of A' in two-dimensional gels is compatible with several mutation models.