Polyamine-stimulated phosphorylation of prostatic spermine-binding protein is mediated only by cyclic AMP-independent protein kinases.
Spermine-binding protein (a rat ventral prostatic protein with high affinity for spermine) was phosphorylated in situ through the action of intrinsic cellular protein kinase(s), suggesting it to be a phosphoprotein in vivo. The purified protein served as a substrate in a number of cyclic AMP-independent protein kinase reactions in vitro, but not for cyclic AMP-dependent, Ca2+ + calmodulin-dependent or Ca2+ + phospholipid-dependent protein kinases. Available data indicate that at least one of the cyclic AMP-independent protein kinases (cytosolic protein kinase C2) may be physiologically relevant in mediating the phosphorylation of this protein. The phosphorylation reaction was stimulated several-fold in the presence of spermine. Spermidine was somewhat less effective, whereas putrescine, cadaverine and 1,6-hexanediamine were minimally active. Phospho amino acid analysis of 32P-labelled spermine-binding protein indicated that phosphoserine was the only labelled phospho amino acid. Spermine-binding protein did not undergo autophosphorylation, or modify the stimulative effect of spermine on the phosphorylation of other substrates such as non-histone proteins. In situ the phosphorylation of spermine-binding protein in tissue from castrated rats was markedly diminished as compared with the normal. Since the phosphorylation of spermine-binding protein appears to be mediated by cyclic AMP-independent protein kinase(s) whose activity in the prostate is under androgenic control, it is suggested that androgen-dependent modulation of the protein kinase(s) exerts a regulatory control (via phosphorylation-dephosphorylation) on the spermine-binding activity and stability of this protein in vivo. Further, since this protein is a substrate for only the cyclic AMP-independent protein kinases, it could serve as a tool for the investigation of such kinases.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism*; D011232:Chemical Precipitation; D002843:Chromatin / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009919:Orchiectomy; D010766:Phosphorylation; D011073:Polyamines / Q000494:pharmacology*; D011467:Prostate / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D000596:Amino Acids; D002352:Carrier Proteins; D002843:Chromatin; D047908:Intracellular Signaling Peptides and Proteins; D011073:Polyamines; C032603:Sbp protein, rat; D000242:Cyclic AMP; D011494:Protein Kinases