Induction of cytoskeletal vimentin and actin gene expression by a tumor-promoting phorbol ester in the human leukemic cell line K562.

The tumor-promoting phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) was found to induce the biosynthesis and deposition of two cytoskeletal components in the human erythroleukemic cell line K562 with apparent Mr = 55,000 and 46,000. A time course showed that maximal changes in these cytoskeletal components occurred as early as 24 h after treatment and were maintained at least as long as 72 h. By immunoprecipitation, one of the induced cytoskeletal components was identified as vimentin. There was approximately a 10-fold induction of vimentin biosynthesis following TPA treatment. The other TPA-induced protein was found to co-migrate with purified actin in sodium dodecyl sulfate-polyacrylamide gels. Neither of these proteins was induced in the closely related human erythroleukemic cell line, HEL. By in vitro protein synthesis directed by total cellular RNA isolated from K562 cells, induction of vimentin biosynthesis was found to correlate with increases in the level of vimentin mRNA activity. A time course showed that vimentin mRNA activity was detectably elevated as early as 3 h after TPA treatment and reached a maximum by 12 h then the level decreased. By RNA dot blot and Northern gel hybridization using a cloned human actin cDNA, we found that there was also an induction of actin mRNA. A time course showed that there was an elevation of actin mRNA as early as 1 h after TPA treatment. The level then increased to a maximum at 6 h, after which the level decreased. These results are consistent with the induction of vimentin and actin gene transcription by TPA in K562 cells.