Effect of poly-basic amino acids on the phosphorylation of various substrate proteins by cytosolic protein-tyrosine kinase from porcine spleen

Purification and characterization of the major tyrosine protein kinase from the human promyelocytic cell line, HL60

The major tyrosine protein kinase from HL60 (a human non-differentiated promyelocytic cell line) has been purified almost to homogeneity as judged by silver-stained SDS/PAGE. The procedure involved four chromatographic steps: DEAE-Sepharose, casein-agarose, cibacron-blue--agarose and hexyl-agarose. The purification resulted in more than 1000-fold enrichment in angiotensin II phosphorylation activity. A gel-sizing experiment, labeling with [35S]ATP[gamma s] and autophosphorylation of the enzyme in the presence of [gamma-32P]ATP, all led to the identification of a single protein species with a molecular mass of about 40 kDa. Western blot experiments showed that this protein does not belong to the src family and is not related to the abl and fes oncogene products. Phosphorylation of angiotensin II and casein by this 40-kDa human promyelocytic kinase was stimulated by high ionic strength especially from class IA metal salts. The Km for ATP was 2 microM and the Vmax 3.1 nmol.min-1.mg-1 using angiotensin II as a substrate. The kinase requires the presence of either Mn2+ or Mg2+ for full activity and utilizes ATP or dATP but not GTP as phosphate donor. Based on numerous biochemical observations, it was possible to demonstrate that kinase is different from any other tyrosine protein kinases described in the literature. This 40-kDa protein was used as a molecular tool for testing some tyrosine protein kinase inhibitors described in the literature. It is one of the rare tyrosine protein kinases purified from human cancer cells to date.

Protein kinase C isozymes epsilon and alpha in murine erythroleukemia cells

Protein kinase C (PKC) has a role in signal transduction during hexamethylene bisacetamide (HMBA)-induced differentiation of murine erythroleukemia cells (MELC). Separation of MELC PKC isozymes by hydroxylapatite chromatography yields a major peak (III) and a minor peak (II) of PKC activity, previously reported to contain the PKC alpha and beta isozymes, respectively. In the present study, we confirm that peak III activity is PKC alpha but show that peak II contains PKC epsilon and little or no PKC beta. Immunoblot analysis with isozyme-specific anti-alpha and anti-epsilon PKC antibodies detected PKC alpha in peak III and PKC epsilon in peak II. Peak III activity was markedly enhanced (up to 20-fold) by phosphatidylserine, diolein, and Ca2+, whereas addition of these cofactors to the reaction mixture stimulated peak II activity only 2- to 4-fold. RNase protection analysis of MELC RNA showed that PKC alpha and PKC epsilon RNAs were in a ratio of approximately 2:1, but PKC beta RNA was barely detectable. Taken together, these data indicate that MELC contain PKC alpha and PKC epsilon but little or no PKC beta.

Identification of the phosphorylation sites of H2B histone by a catalytic fragment of p72syk from porcine spleen

Phosphorylated sites of calf thymus H2B histone were investigated with a catalytic fragment of 72 kDa protein-tyrosine kinase (p72syk). Three of five tyrosine residues in H2B histone can be phosphorylated by this kinase. In this analysis, H2B histone was thoroughly phosphorylated in vitro with [gamma-32P]ATP and the kinase, and then digested with a lysylendopeptidase. The resulting radioactive phosphopeptides were separated by a reverse-phase column on high performance liquid chromatography. Subsequent sequential Edman degradation of the purified phosphopeptides revealed that 40Y, 83Y and 121Y were phosphorylated. 121Y is the major phosphorylated residue in H2B histone. No phosphorylation was detected in 37Y and 42Y. Although the consensus sequence was not defined from these analyses, our data suggest that higher-order structure(s) in addition to primary one may participate in recognition of H2B histone by this protein kinase.

Insulin-sensitive myelin basic protein phosphorylation on tyrosine residues

Rat brain plasma membranes were solubilized in detergent and a glycoprotein-enriched fraction was obtained by lectin affinity chromatography. This glycoprotein fraction contained insulin receptors, as well as protein kinases capable of phosphorylating some exogenously added substrates such as MAP2 (microtubule associated protein 2) and MBP (myelin basic protein), but not ribosomal protein S6. Phosphoamino acid analysis of MAP2 and MBP showed that phosphotyrosine residues, as well as phosphoserine/phosphotheronine residues, were present in both proteins under basal conditions. Whereas the addition of insulin to the rat brain membrane glycoprotein fraction in vitro had no effect on MAP2 phosphorylation, MBP phosphorylation was stimulated 2.7-fold in response to insulin. This phenomenon was dose-dependent, with half-maximal stimulation of MBP phosphorylation observed with 2 nM insulin. Phosphoamino acid analysis of MBP indicated that insulin stimulated the phosphorylation of tyrosine residues nearly three-fold, whereas the phosphorylation of serine or threonine residues was not increased. These results identify MBP as a substrate for the rat brain insulin receptor tyrosine-specific protein kinase in vitro.

Possible endogenous substrate proteins for cytosolic protein-tyrosine kinase from porcine spleen

1. Endogenous phosphate acceptor proteins by cytosolic protein-tyrosine kinase from porcine spleen (CPTK-40) were studied using subcellular fractions of porcine spleen and supernatant fraction of rat various tissues. 2. At least 13 phosphate acceptor proteins ranging from 94 to 26 kDa were observed in all but mitochondrial subcellular fractions. 3. Among the supernatant fraction of rat tissues, brain, testis and spleen contained many phosphate acceptor proteins. 4. The most heavily phosphorylated band of around 55 kDa which was commonly recognized among various tissues was confirmed as tubulin by the immunoreactivity with anti-tubulin antibody. 5. The results obtained in this paper indicate that CPTK-40 has the potential to catalyze the phosphorylation of numerous endogenous proteins including tubulin.

Basic polycations activate the insulin receptor kinase and a tightly associated serine kinase

The effects of cationic polyamino acids on phosphorylation of the insulin and insulin-like growth factor 1 receptor kinases were studied and the following observations were made. (a) Polylysine stimulated both tyrosine and serine phosphorylation of the insulin receptor and of additional proteins present in lectin-purified membrane preparations from rat liver. (b) Polylysine synergized with insulin to enhance phosphorylation of the insulin receptor and of additional proteins (pp40 and pp110). (c) Polylysine effects were more pronounced upon increasing the polylysine chain length. (d) The effect of polylysine was biphasic with an optimum at 100 micrograms/ml. (e) Polylysine was found ineffective in stimulating the phosphorylation of immobilized insulin receptors. Taken together, these findings support the notion that the action of polylysine involves conformational changes and presumably aggregation of soluble receptors. The same effects of polylysine were obtained with highly purified insulin receptor preparations. Under these conditions polylysine enhanced both serine and tyrosine phosphorylation of the insulin receptor, suggesting that polylysine stimulates the activity of the insulin receptor kinase, and of a serine kinase that is tightly associated with the insulin receptor.

Purification and characterization of a cytosolic protein-tyrosine kinase from porcine spleen

A cytosolic protein-tyrosine kinase has been highly purified from porcine spleen using [Val5]angiotensin II as a substrate. The purification procedure involves sequential column chromatographies on phosphocellulose, Sephacryl S-200, casein-Sepharose 4B, heparin-Sepharose CL-6B and anti-(4-aminobenzyl phosphonic acid)--Sepharose 4B. Analysis of the most highly purified preparation by SDS/PAGE revealed a major silver-stained band of molecular mass 40 kDa. The 40-kDa cytosolic protein-tyrosine kinase was purified approximately 10,000-fold with an overall yield of about 7%. It had autophosphorylation activity which was carried out by intramolecular catalysis. The stoichiometry of phosphate incorporation was about 1 mol phosphate/mol enzyme. In the autophosphorylation reaction, the apparent Km value for ATP was relatively low, 0.35 microM; Mn2+ was slightly preferred to Mg2+ as divalent cation. [Val5]Angiotensin II phosphorylation activity of the 40-kDa kinase increased with the amount of phosphate incorporated into the enzyme. A phosphate exchange reaction was observed during the autophosphorylation. These results suggest that the 40-kDa kinase described here is a different type of protein-tyrosine kinase than the enzymes so far reported.

Polyamines and basic proteins stimulate activation by cAMP and catalytic activity of Mucor rouxii cAMP-dependent protein kinase

Partial activation of Mucor rouxii cAMP-dependent protein kinase by cAMP was obtained when kemptide was used as substrate, but complete activation was attained with cAMP plus protamine or histone. Full activation could not be achieved by increasing kemptide or cAMP concentration. Complete activation by cAMP could be obtained by addition of 10 microM polylysine, 10 microM lysine-rich histone or 0.5 mM spermine plus spermidine. The degree of stimulation could be up to 5-fold, depending on the amount of enzyme in the assay. The same concentrations of polycations increased 1.5-2.3-fold the Vmax of kemptide phosphorylation by the free catalytic subunits of both Mucor and bovine heart protein kinases; 10 microM polyarginine inhibited completely the activity of both enzymes.

Diverse effects of poly-basic amino acids, heparin and ionic strength on the phosphorylation of various substrates by cytosolic protein-tyrosine kinase from porcine spleen

1. Effects of poly-basic amino acids, heparin and ionic strength on the activity of cytosolic protein-tyrosine kinase from porcine spleen (CPTK-40) have been studied. 2. Both polylysine and polyarginine stimulated the phosphorylation of [Val5]angiotensin II and E11 G1 (synthetic peptide of EDAEYAARRRG), but could neither stimulate nor inhibit the phosphorylation of random copolymers; poly(EY)4:1 and poly(EAY)6:3:1. 3. Heparin stimulated the phosphorylation of poly(EY)4:1 by 2.5-fold, however, it inhibited those of E11G1, poly(EAY)6:3:1, casein and H2B histone. 4. Elevation of ionic strength of either NaCl, KCl or (NH4)2SO4 stimulated the phosphorylation of poly(EY)4:1 by greater than 5-fold, but inhibited those of casein, tubulin, H2B histone, E11G1 and poly(EAY)6:3:1. 5. These effectors did not change the Km for substrates but increased the Vmax. 6. These results suggest that the effects of poly-basic amino acids, heparin and ionic strength on the activity of CPTK-40 are mainly on the substrates employed rather than on the enzyme itself.

Phospholipids differently modulate the activity of cytosolic protein-tyrosine kinase from porcine spleen

Effect of membrane phospholipids on the activity of cytosolic protein-tyrosine kinase from porcine spleen (CPTK-40) has been studied. Using poly(Glu Na, Tyr)4:1 as a substrate, phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine had stimulatory effects on that phosphorylation activity, however phosphatidic acid had inhibitory and phosphatidylinositol had no effects. Similar results were obtained using[Val5]angiotensin II as a substrate. On the other hand using basic protein (H2B histone and myelin basic protein) as substrates, phosphatidic acid stimulated the activity of CPTK-40, while phosphatidylinositol inhibited the activity. Phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine caused different effect on the activity of CPTK-40 depending on the substrate employed. However using acidic protein (tubulin and casein) as substrates, the activity of CPTK-40 was neither stimulated nor inhibited by any phospholipids. These results suggest that phospholipids may modulate the activity of CPTK-40.