Characterization of adenosine cyclic 3':5'-monophosphate-binding proteins in human neuroblastoma
Imashuku, S.; Fossett, M.C.; Green, A.A.
Cancer Research 39(8): 3006-3013
1979
ISSN/ISBN: 0008-5472 PMID: 222441 Document Number: 142168
Cyclic(c)AMP-binding proteins were studied in human neuroblastoma, a tumor thought to be responsive to the antitumor effect of cAMP. Cytosol from this tumor contains at least 6 high-affinity, cAMP-binding proteins with apparent MW ranging from 36,000-55,000 by sodium dodecyl sulfate:polyacrylamide gel electrophoresis. The bands representing the cAMP-binding proteins were detected on the gel by photoaffinity labeling with 8-azido-cAMP-[32P]triethylammonium salt. However, only 2 types of cAMP-dependent protein kinases, a minor type I and a major type II, were resolved by DEAE-cellulose column chromatography. The cAMP-binding proteins were copurified with either type I or II protein kinases. A protein with a MW of 47,000 seems to represent the regulatory subunit of type I, and 2 proteins with MW of 55,000 and 51,000 appear to be heterogenous regulatory subunits of type II enzyme. These 3 proteins incorporated 60-90% of the total 8-azido-cAMP-[32P]triethylammonium salt in the majority of tumor tissues examined. Other smaller MW proteins were the proteolytic products of these 3 proteins. Proteolysis of cAMP-binding proteins increased in vitro during experimental procedures and data demonstrate that it probably also occurs in vivo. However, it is unknown if the proteolytic activity in tumor cells may affect the normal function of the native regulatory subunits of cAMP-dependent protein kinases. The relative amounts of proteins with MW of 55,000, 51,000 and 47,000 are variable from one tumor to another. Since these cAMP-binding proteins may differ functionally, it is essential to define their roles in the regulation of growth and differentiation of human neuroblastoma.