A study of 3':5'-cyclic mononucleotide-dependent protein kinase from canine prostate glands

Differential androgenic control of prostatic cytosolic cAMP-dependent and -independent protein kinases

Whether or not various cytosolic protein kinases (and especially the type I cAMP-dependent protein kinase) of rat ventral prostate are specifically regulated with respect to total activity or specific activity by androgen has been investigated. Following androgen deprivation, the total activity per prostate of cAMP-dependent protein kinase (with histone as substrate) changed little at 24 h, declining by about 20% at 96 h. Under these conditions, its specific activity remained unaltered at 24 h, but was markedly enhanced at 96 h postorchiectomy. Type II cAMP-dependent protein kinase in rat ventral prostate cytosol was the only form of cAMP-dependent protein kinases present as determined by measurement of catalytic activity as well as [32P]-8-N3-cAMP binding to the regulatory subunits. There was no alteration in the distribution of the isoenzymes of cAMP-dependent protein kinases or the response of these kinase activities to cAMP owing to castration of animals. The prostatic cytosol also contains free regulatory subunit (with molecular weight similar to that of regulatory subunit R1) which coelutes with type II cAMP-dependent protein kinase. This finding was confirmed by using [32P]-8-N3-cAMP photoaffinity labeling of cAMP-binding proteins. With respect to cAMP-independent protein kinase (measured with dephosphophosvitin as substrate), a decline of 31% in its specific activity was observed in cytosol of prostates from rats castrated for a period of 24 h without significant further change at later periods following castration. However, there was a marked progressive reduction in total activity of this enzyme per prostate (loss of 72% at 96 h postorchiectomy). The increase in specific activity of cAMP-dependent, but not cAMP-independent, protein kinase in the face of decreasing total activity in the cytosol at later periods of castration (e.g., at 96 h) may reflect a slower loss of the former enzyme protein than the bulk of the cytosolic proteins. Administration of testosterone to castrated animals prevented these changes. These data do not indicate a specific regulation by steroid of the type I cAMP-dependent protein kinase in the prostate. Rather, the cAMP-independent protein kinase (with dephosphophosvitin as substrate) appears to be modulated by the androgenic status of the animal.

Studies on glutathione metabolism in ventral prostate and chemically induced prostatic carcinoma in rats

Glutathione content and the activity of glutathione reductase were examined in ventral prostate and chemically induced 11095 squamous-cell prostatic carcinoma in rats. Castration produced a significant reduction in the levels of reduced (GSH) and oxidized (GSSG) glutathione and glutathione reductase activity in the prostate. Replacement of testosterone (50 mg/kg) daily for 7 days to castrated animals elevated the reduced glutathione level and the activity of glutathione reductase almost to normal limits. Squamous-cell carcinoma was implanted in castrated and intact animals. Tumor growth in normal rats produced a decrease of almost 30% in the weight of the ventral prostate at 21 days post-implantation, although the glutathione levels remained unaffected. Much greater activity of glutathione reductase was detected in the tumor in comparison to the values noted for the normal tissue. The tumor also showed significantly higher values for the GSH/GSSG ratio. No apparent difference could be found in the rate of the growth of tumors whether implanted in normal or castrated animals. The levels of reduced and oxidized glutathione and glutathione reductase activity also seemed identical in tumors obtained from both groups of animals. Administration of testosterone (50 mg/kg) or beta-estradiol (2 mg/kg) daily for 11 days to tumor-bearing castrated animals did not alter the levels of glutathione and glutathione reductase activity. A significantly higher level of blood reduced glutathione was found in tumor-bearing rats in comparison to that seen for the normal subjects. Our results demonstrate that androgen depletion and replacement therapy influence the metabolism of glutathione in rat ventral prostate. Squamous-cell carcinoma of the prostate appears to differ from the normal tissue with respect to the observed androgen effects. There is dissimilarity in the metabolism of glutathione in the two tissues since greater activity of glutathione reductase and lower values of reduced glutathione were seen in the tumor as compared to those of the ventral prostate. Treatment with beta-estradiol, an antiprostatic agent, does not seem to influence the growth or glutathione metabolism of squamous-cell carcinoma of the prostate. The observed changes in blood glutathione levels might prove to be useful as an index of rapid growth of the neoplastic tissue.

3',5'-cyclic-nucleotide-dependent protein kinase of squamous cell carcinoma of the prostate

An adenosine 3'5'-cyclic-monophosphate (Cyclic AMP)-dependent protein kinase has been identified and partially purified from the rat prostate tumor induced by 20-methylcholanthrene. This enzyme is stimulated 2- to 3-fold by the nucleotide. Equilibrium studies at pH 5.0 suggest the presence of a major class of binding site for cyclic AMP with an association constant of approximately 10(8) M-1. The concentration of binding site is about 1 pmol/mg of protein of the enzyme preparation. The enzyme is stimulated by other cyclic nucleotides as well, but only by higher concentrations. In comparing the ability of different histone subfractions, casein and protamine, to serve as substrate for this particular protein kinase, maximal cyclic-AMP-dependent enzyme activity was observed with histones. The results suggest that factors contributing to the malignant growth of the prostatic tissue do not directly involve changes in the characteristics of a cyclic-AMP-dependent protein kinase.

The regulation of cell proliferation by calcium and cyclic AMP

Calcium, in partnership with cyclic AMP, controls the proliferation of non-tumorigenic cells in vitro and in vivo. While it does not seem to be involved in the proliferative activation of cells such as hepatocytes (in vivo) or small lymphocytes (in vitro), it does control two later stages of prereplicative (G1) development. It must be one of the very many regulatory and permissive factors affecting early prereplicative development, because severe calcium deprivation reversibly arrests some types of cell early in the G1 phase of their growth-division cycle in vitro. However, calcium more specifically and much more often regulates a later (mid or late G1) stage of prereplicative development. Thus, regardless of its severity or the type of cell, calcium deprivation in vitro or in vivo reversibly stops proliferative development at that part of the G1 phase in which the cellular cyclic AMP content transiently rises and the synthesis of the four deoxyribonucleotides begins. The evidence points to calcium and the cyclic AMP surge being co-generators of the signal committing the cell to DNA synthesis. The evidence is best explained so far by the cyclic AMP surge causing a surge of calcium ions which combine with molecules of the multi-purpose, calcium-dependent, regulator protein calmodulin (CDR) somewhere between the cell surface and the cytosol. The resulting Ca-calmodulin complexes then stimulate many different (and possibly membrane-associated) enzymes such as protein kinases, one of which produces the DNA-synthetic initiator. Calcium has little or no influence on the proliferation of tumor cells. Some possible explanations of this very important loss of control are considered.

Alteration in testicular cyclic AMP system in the rat following vasectomy

Endogenous cyclic AMP levels and the activities of adenylate cyclase, cyclic AMP-dependent and independent protein kinases were examined in testes of mature rats bilaterally vasectomized for one, three and seven months. Although no significant alteration in testicular cyclic AMP was detected one month following vasectomy, marked decreases (by 55% and 32%, respectively) were seen three and seven months postvasectomy. Likewise, vasectomy also resulted in a significant decrease (by 25%) in the activity of testicular adenylate cyclase three and seven months after vasectomy. Although soluble cyclic AMP-dependent protein kinase activity remained unaffected three months postvasectomy, the activity of the cyclic nucleotide-dependent enzyme was significantly increased (by 21%) when compared to the sham-operated controls. Furthermore, while the protein kinase ratio (--cyclic AMP/+cyclic AMP) was decreased in animals vasectomized for three months, the ability of the enzyme to bind (3H) cyclic AMP in vitro was significantly enhanced (18%). Rats vasectomized for seven months showed similar biochemical alterations but the effects of this procedure were more pronounced. Moreover, while short-term vasectomy increased the responsiveness of seminiferous tubular adenylate cyclase to in vitro stimulation by follicle stimulating hormone, the activity of the enzyme was also increased (by 100%) in the presence of luteinizing hormone in vasectomized rats. These data raise the possibility that changes in testicular function seen following vasectomy may be related to the alterations in cyclic AMP metabolism as well as in the sensitivity of testicular adenylate cyclase to regulation by gonadotropins.