Calcium-dependent regulatory protein of cyclic nucleotide metabolism in normal and transformed chicken embryo fibroblasts.

Abstract

The concentration of a Ca-binding protein modulator of 3'':5''-cyclic nucleotide phosphodiesterase (EC 3.1.4.17;3'':5''-cyclic nucleotide 5''-nucleotidohydrolase) activity is increased in chicken embryo fibroblasts on transformation by Rous sarcoma virus. This modulator protein from fibroblasts, which has roughly the same molecular size, charge and functional properties as that isolated from chicken brain comprises approximately 1.32% of the soluble protein in homogenates of fibroblasts infected and transformed by Rous sarcoma virus. The modulator comprises approximately 0.30% of the soluble protein in homogenates of normal fibroblasts from confluent cultures and 0.36% of the soluble protein in homogenates of fibroblasts infected with a transformation-defective mutant of Rous sarcoma virus. Modulator levels in normal fibroblasts at subconfluent cell densities are 0.42-0.76% of the homogenate soluble protein, i.e., between that found in confluent normal fibroblasts and fibroblasts transformed by Rous sarcoma virus. These observations suggest that the levels of the modulator protein are elevated under conditions in which chicken embryo fibroblasts are undergoing rapid growth and have decreased cyclic AMP levels.