Pathways for degradation of the catalytic subunit of cAMP-dependent protein kinase differ in wild-type and kinase-negative S49 mouse lymphoma cells.
The catalytic subunit of cAMP-dependent protein kinase radiolabeled with [35S]methionine in wild-type S49 mouse lymphoma cells was degraded with half-lives of approximately 9.2 h in unstimulated cells and approximately 4.5 h in cells stimulated with a membrane-permeable cAMP analog. Turnover in kinase-negative mutant cells was about three times faster than in stimulated wild-type cells and appeared to involve a unique 47-kDa intermediate. Levels of catalytic subunit protein revealed by Western immunoblotting were consistent with the measured differences in turnover, but whereas the protein was mostly soluble in wild-type cell extracts, it was almost entirely insoluble in the mutant cell extracts. A substantial fraction of the catalytic subunit labeled in a 5-min pulse was soluble in kinase-negative cell extracts, but most of this material was rendered insoluble by incubating the cells for an additional 30 min before extraction. Degradation of the catalytic subunit in kinase-negative, but not in wild-type, cells was inhibited strongly by two specific peptide aldehyde inhibitors of the proteasomal chymotrypsin-like activity. An inhibitor of the proteasomal protease that prefers branched-chain amino acids had less of an effect on catalytic subunit degradation in the mutant cells.
Lee
S L
SL
Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190, USA.
Steinberg
R A
RA
D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation; D006868:Hydrolysis; D008223:Lymphoma / Q000201:enzymology*; D051379:Mice; D014407:Tumor Cells, Cultured
D017868:Cyclic AMP-Dependent Protein Kinases