Distribution and Properties of Type I and Type II Binding Proteins in the Cyclic Adenosine 3′:5′-Monophosphate-dependent Protein Kinase System in Wilms' Tumor

Abstract

We compared the relative amounts and properties of cyclic adenosine 3′:5′-monophosphate (cAMP)-binding proteins in surgical specimens of Wilms' tumor and normal kidney. Cytosolic fractions of both tissues contained type I and type II isozymes of cAMP-dependent protein kinase (adenosine triphosphate: protein phosphotransferase, EC 2.7.1.37). Among tumor samples, the mean ratio of type I to type II cAMP-binding activity was 2.76 ± 0.52 (S.D.) contrasted with 1.36 ± 0.23 for normal kidney (p < 0.001). The total soluble cAMP-binding activities in normal and malignant tissues differed only slightly. Photoaffinity labeling of cytosol from either tissue, using cyclic adenosine 3′:5′-[8-azido-³²P]monophosphate, disclosed three cAMP-binding proteins (M_r 47,000, 51,000, and 55,000) that were identified as regulatory subunits of the holoenzyme. Three lower-molecular-weight proteins with unknown function were considered to be proteolytic products of the larger proteins. The M_r 47,000 protein, a monomeric regulatory subunit of type I kinase, was clearly the dominant protein in tumor specimens, but it was much less abundant in normal kidney. The temperature sensitivities of the cAMP-binding proteins and their dissociation constants for cyclic adenosine 3′:5′-[8-azido-³²P]monophosphate incorporation did not differ appreciably between tumor and normal tissues. Wilms' tumor appears to have a full complement of regulatory subunits of cAMP-dependent protein kinase that are capable of normal cellular function.