cAMP-independent protein kinase activity is correlated with growth of rat mammary tumors

An important portion of the protein kinase activity in the 7,12-dimethylbenz(a)anthracene (DMBA) induced rat mammary tumour is inhibited by the bioflavonoid quercetin (10^-4 M). By partial purification on a DEAE Cellulose column it was shown that the quercetin-inhibitable enzyme activity can be eluted in a separate peak which contains markedly reduced cAMP-dependent protein kinase activity. Since quercetin does not affect the cAMP-dependent protein kinase activity, this drug becomes a potent tool for the quantitation of this special activity in the tumor. By hormonal manipulation, namely ovariectomy and estrogen treatment, it was shown that changes in the growth rate of the tumour were closely correlated with the magnitude of these special protein kinase activities. These results suggest a possible cause-and-effect relationship between cyclic AMP-independent protein kinase activity and tumour malignancy in this chemically induced tumor. These data are similar to recent findings in viral-induced malignant transformation.