Effects of estrogen and prolactin on thymidine kinase isozyme activities in DMBA-induced rat mammary tumor.

Effects of prolactin or estrogen on the activity of the pyrimidine salvage pathway enzyme thymidine kinase (TK) in 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors were investigated in ovariectomized rats. Prolactin induced by perphenazine administration significantly enhanced the activities of total TK or its isozyme in the tumors. This specific TK isozyme separated by DEAE-cellulose column chromatography was suggested to be involved in DNA synthesis because it was not affected by dCTP. Its Mr was estimated to be approx. 100 000 by high-performance liquid chromatography. In contrast, estrogen alone did not raise the activity of the specific TK isozyme in the tumors.