Enzymic characteristics and effects of testosterone treatment on nucleolar and chromatin-associated histone phosphokinase activity of rat ventral prostate

Differential localization and androgen sensitivity of prostatic nuclear protein kinases in euchromatin and heterochromatin fractions

We have examined the distribution and androgenic regulation of protein kinases and phosphoproteins in euchromatin and heterochromatin fractions of rat ventral prostate chromatin. Available procedures to prepare euchromatin and heterochromatin fractions were found to result in the loss of various chromatin-associated protein kinases even though there was no gross change in the gel electrophoretic profile of proteins in these fractions. This loss was prevented by the addition of 0.5 mM phenylmethylsulfonyl fluoride throughout the preparative procedures, which indicates that the protein kinases associated with the chromatin may be particularly susceptible to proteolytic degradation during further subfractionation. By utilizing an improved method for fractionation of chromatin, we have demonstrated a marked enrichment of protein kinase activity (towards phosvitin and endogenous chromosomal proteins) in the euchromatin fraction as compared with heterochromatin. Both of these fractions were also examined for the incorporation of 32P into two main classes of nonhistone proteins (namely, H2SO4-soluble and -insoluble nonhistones). The amount of 32P incorporated into heterochromatin-associated proteins of both classes was markedly less than that in the euchromatin-associated proteins. Protein kinase activities (especially those active towards phosvitin and nonhistone proteins) in the euchromatin fraction as compared with the heterochromatin were significantly reduced within 24 h after androgenic deprivation in the animal. The decreased phosphorylation of nonhistone proteins could be attributed to the loss of endogenous protein kinase activity. The results indicate that not only are chromatin-associated protein phosphokinases preferentially localized in euchromatin fractions but also that these euchromatin-associated protein kinases display the greatest sensitivity to androgenic status of the animal.

Differential effects of polyamines on the phosphorylation of chromatin-associated proteins

Studies are presented on the nature of chromatin-associated phosphoproteins whose phosphorylation is influenced by polyamines. After labelling with 32P, chromatin-associated proteins were separated into four fractions. Fraction I comprised neutral and basic non-histone phosphoproteins, including high-mobility-group non-histones; fraction II consisted mostly of histones; fraction III consisted of a class of (salt-soluble) acidic non-histone phosphoproteins; and fraction IV consisted of residual (salt-insoluble) acidic non-histone phosphoproteins. The average relative distribution of protein in the four fractions (I-IV) was about 1:4:2:1 for both liver and prostate. However, tissue-dependent differences were observed in the incorporation of 32P in various protein fractions. In the presence of polyamines (e.g. 1 mM-spermine or 2 mM-spermidine) maximal stimulation of phosphorylation was observed in non-histone proteins of fraction I (160-180%), followed by that in non-histone proteins of fraction III (80-110%). The phosphorylation of residual non-histone proteins in fraction IV, and the small extent of phosphorylation of histones in fraction II, remained unaltered in the presence of polyamines. Thus polyamines do not stimulate the phosphorylation of all non-histone proteins; their stimulative effect is most prominent in the phosphorylation of neutral and basic non-histone proteins and a class of salt-soluble acidic non-histone proteins. In accord with our hypothesis, these differential effects of polyamines on phosphorylation of endogenous non-histone proteins may relate to the conformation of these substrates rather than to endogenous kinases.

Presence and characterization of two protein kinase activities in human seminal fluid

The presence of two protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) activities has been demonstrated in human seminal fluid, utilizing partially dephosphorylated phosvitin and lysine-rich histones as model acceptor substrates. Both kinase activities were maximal in the presence of MgCl2 and a sulfhydryl-protecting agent such as dithiothreitol; however, the histone kinase was stimulated to a greater extent by the latter. The histone kinase displayed a broad shoulder of activity at pH values of 7.1 to 7.6 with optimal activity at pH 8.0, and was inhibited by increased ionic strength (53% at 160 mM NaCl) and by the cyclic AMP-dependent protein inhibitor from rabbit muscle. The kinase activity towards phosvitin exhibited a broad pH profile with maximal activity at pH 7.2, was slightly stimulated by NaCl (20% at 160 mM), and was unaffected by the cyclic AMP-dependent protein kinase inhibitor. Kinetic studies revealed more than one apparent Km for the protein substrates and ATP. These differences in enzymic properties of kinase activities towards phosvitin and lysine-rich histones strongly indicate the presence of multiple enzymes. It appears that the histone kinase activity is attributable to the free catalytic subunit of a cyclic AMP-dependent enzyme. The protein kinase activities of seminal fluids from vasectomized men were 12-20% of those found for seminal fluids of normal men. This suggests that sperm may be a major source of protein kinase activities in seminal fluid.

Phosphoproteins and protein kinase activities of ventral prostate chromatin during sexual maturation in the rat

1. In the ventral prostates of rats undergoing normal sexual development, chromatin-associated phosphokinase activities toward dephosphophosvitin and lysine-rich histones were maximal at 48 days of age, whereas phosphorylation of endogenous chromosomal proteins was greatest in the sexually mature adult. 2. Polyacrylamide gel electrophoretic analysis of chromatin proteins from these animals revealed age-dependent changes in the amount of phosphorylation of specific proteins. 3. These were most evident in highly phosphorylated H2SO4-soluble nonhistone proteins and in those nonhistones (13-16 K and 20-35 K mol. wt) which are insoluble in H2SO4.

Nuclear envelope of the seminal-vesicle epithelium

The nuclear envelope of seminal-vesicle epithelium was isolated by a procedure involving enzymic digestion with deoxyribonuclease I, sonication in the presence of 0.34 M-sodium citrate, and centrifugation through sucrose density gradients. The mass of envelope DNA was only 0.8% of that of envelope protein, and by transmission electron microscopy the envelope was 98-99% pure. We showed that the envelope possess a protein kinase activity which is uninfluenced by cyclic nucleotides. Both lysine-rich histone and dephosphophosvitin as substrates gave a greater specific activity than did envelope protein itself. Optimum requirements with respect to Na+, Mg2+, pH and ATP were established for each substrate, and the influence of other factors on enzyme activity was investigated. Data, obtained mainly with the use of lysine-rich histone, are presented which indicate that nuclear envelope from intact and 96 h-castrated guinea pigs may have equal protein kinase activities and, in separate experiments, equal phosphoprotein phosphatase activities. Clarification of these initial observations must await identification of the natural substrates or the envelope's phosphorylation-dephosphorylation reactions.

A modified paper-binding procedure for the assay of nucleus-associated protein phosphokinases

Previously existing paper-binding assay procedures gave results with large variations when employed for the measurement of nucleus-associated protein phosphokinase activities. However, a modified method, utilizing the binding of 32P-labeled phosphoprotein substrates to paper and employing washing procedures in 20% trichloroacetic acid at 60 degrees to 70 degrees C, gave highly reproducible results. This modified procedure was satisfactory with either chromatin or a nonhistone protein fraction derived therefrom as a source of enzyme, and dephosphophosvitin, lysine-rich histones, or casein as phosphoprotein substrates.

Effects of polyamines on prostatic chromatin- and non-histone-protein-associated protein kinase reactions

Studies are presented on the influence of polyamines on prostatic chromatin- and non-histone-protein-associated protein kinase reactions involving both exogenous and endogenous substrates. The activities toward the model acidic protein substrate, dephosphophosvitin, were maximal at 160--200mM-NaCl (or -KCl or -NH4Cl). Under these conditions, spermidine and spermine added in concentrations up to 2mM were essentially without effect. However, without addition of NaCl to the medium, marked stimulation of these reactions was elicited by these polyamines at 1--2mM concentrations. The stimulatory effects were not due to non-specific changes in the ionic strength or to substitution of spermine for Mg2+, as maximal stimulation by 1 mM-spermine was observed only at optimal (2--4mM) Mg2+ concentrations. Qualitatively similar effects of polyamines were observed with enzyme preparations from the prostates of castrated rats, and with chromatin and non-histone-protein preparations from other tissues besides ventral prostate. When phosphorylation of endogenous non-histone proteins of the chromatin was measured, spermine stimulated both the initial rates and the final extent of transphosphorylation, even in the presence of optimal concentration of NaCl. By contrast, spermine or spermidine had no effect on the chromatin- and non-histone-protein-associated protein kinase reactions determined with lysine-rich histones as substrates. Chemically NN-dimethylated dephosphophosvitin was a less active substrate for the chromatin-associated protein kinase, but its phosphorylation was more markedly stimulated by spermine in comparison with unmodified dephosphophosvitin. These observations hint that the polyamine stimulations of the various protein kinase reactions may be due to effects on the conformations of the non-histone protein substrates rather than on the kinases themselves.

Acidic-phosphoprotein phosphatase activity of rat ventral prostate nuclei: apparent lack of effect of androgens

A protein phosphatase activity has been demonstrated in nuclei of rat ventral prostate utilizing 32P-labelled phosvitin as a model acidic phosphoprotein substrate. This phosphoprotein phosphatase has a pH optimum of 6.7, is unaffected by the sulphydryl protecting agent 2-mercaptoethanol, and requires a divalent cation for maximal activity. Of the various divalent cations tested, Mg2+ is the most effective in reactivating the EDTA-inhibited enzyme. The phosphatase is inhibited by sodium flouride, sodium oxalate, N-ethylmaleimide, ATP and ADP but is relatively insensitive to ammonium molybdate. Increased ionic strength of the reaction medium also causes a reduction in the enzyme activity, e.g., by 48% at 200 mM sodium chloride. The activity of the acidic phosphoprotein phosphatase did not change significantly at 48 h or 96 h post-orchiectomy when expressed per unit of nuclear protein. However, it is reduced by approx. 30% at these times after castration if based on DNA content. The decline in activity per nucleus reflects the decrease in the realtive nuclear protein content observed at 48 h or 96 h post-orchiectomy. This suggests that the decline in the phosphorylation of prostatic nuclear acidic proteins which occurs upon androgen withdrawal is not due to increased nuclear phosphatase activity.