CYCLIC ADENOSINE 3'-5'-MONOPHOSPHATE RECEPTOR PROTEINS IN HORMONE-DEPENDENT AND HORMONE-INDEPENDENT RAT MAMMARY-TUMORS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 41  (5) , 1840-1846
Abstract
Three major types of cAMP receptor proteins with MW of 39,000, 48,000 and 56,000 were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the tumor cytosols. The MW 48,000 and 56,000 receptor proteins appeared to be the regulatory subunits of cAMP-dependent protein kinase types I and II, respectively, and the MW 39,000 receptor protein was the proteolytic fragment of the MW 56,000 receptor protein. The relative amounts of these cAMP receptor proteins varied from one tumor type to another and showed no correlation with the hormone dependency of tumors. Under 2-dimensional gel electrophoresis, the MW 56,000 receptor protein from hormone-independent tumors migrated as a doublet and shifted to a more acidic or more basic charge than that of the receptor protein of hormone-dependent tumors. The alteration of the charge of the receptor did not affect the affinity for cAMP binding; hormone-dependent and hormone-independent tumor cytosols exhibited the Kd for cAMP of .apprx. 10-8 M. The MW 56,000 cAMP receptor protein from hormone-dependent tumors exhibited self-phosphorylation, but that from hormone-independent tumors did not. The diethylaminoethyl cellulose elution profiles of cAMP receptor proteins differed between hormone-dependent and -independent tumors; cAMP binding activity from hormone-dependent tumors coeluted with cAMP-dependent protein kinase activity, whereas most of the cAMP binding activity from hormone-independent tumors eluted at a higher ionic strength than did cAMP-dependent protein kinase activity. The charge alteration of cAMP receptor proteins, which appears to occur at a site remote from that of cAMP binding, may be associated with the hormone independency of mammary tumors.

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