title: Age-dependent changes in murine protein kinase and protease enzymes.
abstract: Hormone responsiveness is mediated by signal transduction mechanisms involving second messengers, such as cAMP and Ca2+, which regulate reversible changes in the phosphorylation state of proteins. During senescence individuals frequently exhibit a diminished responsiveness to hormones. We examined changes in enzymes involved in protein phosphorylation reactions that might account for this decreased adaptiveness in old mice, and observed the following post-maturational changes: (1) cAMP-dependent protein kinase (Pk-A) specific activity decreased in spleen cytosol and in the particulate fractions of lung, spleen and liver of 24-month-old mice as compared to 2-month-old mice. Splenic cytosolic Pk-A activity decreased by 18 months of age, while particulate activity decreased by 6 months; (2) The amount of 8-N3-[32P]cAMP, a photoaffinity analog of cAMP, incorporated into Pk-A regulatory (R)-subunits from spleen and liver particulate fractions decreased, while photolabeling of R-subunit degradative products with this analog in heart and spleen cytosol increased. (3) Age-dependent increases in membrane-associated protease activities were found in all organs, along with a decrease in cytosolic lung calpain activity. These proteolytic changes may account for the enhanced R-subunit degradation and decreased Pk-A activities observed during senescence. (4) Age-dependent alterations in Ca2+/phospholipid-dependent protein kinase (Pk-C) are organ specific: lung, liver, brain, and heart demonstrate no change in Pk-C activity, while spleen exhibits decreased activity. We hypothesize that these age-dependent alterations in kinase and proteolytic activities may be in part responsible for changes in cellular response to hormonal stimulation, differentiation signals, and antigen responsiveness during senescence.
authors.affiliation: Molecular and Environmental Toxicology Program, School of Pharmacy, University of Colorado, Boulder 80309-0297.
authors.forename: E J
authors.initials: EJ
authors.lastname: Blumenthal
authors.forename: A M
authors.initials: AM
authors.lastname: Malkinson
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D001386:Azides / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D008297:Male; D051379:Mice; D009929:Organ Size; D011480:Protease Inhibitors / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*
chemical_list: D001386:Azides; D011480:Protease Inhibitors; C017042:8-azidoadenosine-3',5'-monophosphate; D000242:Cyclic AMP; D011494:Protein Kinases; D011493:Protein Kinase C; D002154:Calpain