Phosphorylation of small peptides by spleen TPK-IIA, a tyrosine protein kinase stimulated by polylysine and by high ionic strength

In silico studies of potential phosphoresidues in the human nucleophosmin/B23: its kinases and related biological processes

Human nucleophosmin/B23 is a phosphoprotein involved in ribosome biogenesis, centrosome duplication, cancer, and apoptosis. Its function, localization, and mobility within cells, are highly regulated by phosphorylation events. Up to 21 phosphosites of B23 have been experimentally verified even though the corresponding kinase is known only for seven of them. In this work, we predict the phosphorylation sites in human B23 using six kinase-specific servers (KinasePhos 2.0, PredPhospho, NetPhosK 1.0, PKC Scan, pkaPS, and MetaPredPS) plus DISPHOS 1.3, which is not kinase specific. The results were integrated with information regarding 3D structure and residue conservation of B23, as well as cellular localizations, cellular processes, signaling pathways and protein-protein interaction networks involving both B23 and each predicted kinase. Thus, all 40 potential phosphosites of B23 were predicted with significant score (>0.50) as substrates of at least one of 38 kinases. Thirteen of these residues are newly proposed showing high susceptibility of phosphorylation considering their solvent accessibility. Our results also suggest that the enzymes CDKs, PKC, CK2, PLK1, and PKA could phosphorylate B23 at higher number of sites than those previously reported. Furthermore, PDK, GSK3, ATM, MAPK, PKB, and CHK1 could mediate multisite phosphorylation of B23, although they have not been verified as kinases for this protein. Finally, we suggest that B23 phosphorylation is related to cellular processes such as apoptosis, cell survival, cell proliferation, and response to DNA damage stimulus, in which these kinases are involved. These predictions could contribute to a better understanding, as well as addressing further experimental studies, of B23 phosphorylation.

Tyrosine protein kinase assays

Protein kinases form a large family of enzymes that play a major role in a number of live processes. The study of their action is important for the understanding of the transformation mechanisms and of the normal and pathological growth events. The quality of an enzyme assay is often the key point of an enzymatic study. It must be flexible and compatible with various experimental conditions, such as those for the purification process, the screening of inhibitors and the substrate specificity studies. As will be shown in the present review, two categories of substrates, peptidic and proteic, should be distinguished. The use of peptide substrates facilitates the determination of the recognition requirements of the enzyme and of the kinetic effects of even minute variations in their sequence. These linear peptide structures are assumed to mimic a complex interaction between the enzyme and a protein substrate in which distant amino acids in the sequence are vicinal in the folded substrate. Less amenable to a systematic study, but probably more adequate to investigate the natural substrate of a given kinase, are the proteic substrates. Obviously the tools to measure protein kinase activities are not the same in these two cases. The main difficulty in assaying protein kinases is the use of labelled gamma-ATP, mostly at large excess concentration, since the final product of the reaction has to be separated from the non-reacted labelled ATP. In the case of peptide substrates, the difficulty is to separate them from ATP basing on differences of molecular mass. Despite the efforts of many investigators to rely upon differences in solubility, in charges or in "affinity", this separation, which is crucial for the assay, is still an unsolved experimental problem. Chromatographic, as well as electrophoretic assays appeared relatively late in this domain, and more work in assessing new methodologies might bring new breakthroughs in the next few years. Specific, simple and reliable kinase assays are still a major challenge. Their improvement will help to conduct specificity studies, to elucidate complex growth mechanisms in which they are involved and to discover more selective potent inhibitors.

Tyrosine protein kinase inhibition and cancer

The various aspects of the research on tyrosine protein kinase inhibition and its connections with cancer are presented. The emphasis was made on the theoretical low toxic side effects of specific tyrosine protein kinase inhibitors. Particularly, the strategy of finding peptidic substrate-derived inhibitors or modulators is discussed, with an almost complete compendium of the tyrosine protein kinase peptidic substrates published so far. A series of data has been gathered that may serve as a basis for the discovery of selective and specific tyrosine protein kinase inhibitors by screening on molecular and cellular models. The potential of SH2 domain-interfering agents are also presented as a promising route to new anticancer compounds.

Substrate phosphorylation capacities of the major tyrosine protein kinase from the human promyelocytic cell line, HL-60

The major tyrosine protein kinase, HPK40, isolated from HL-60, the preparation of which is described elsewhere (Ernould, A.P., Ferry, G., Barret, J.M., Genton, A. and Boutin, J.A., Eur. J. Biochem., 214, 503-514), was investigated as to its specificity on a number of peptides and proteins. It was found that HPK40 can phosphorylate histones (except histone H4), casein, acid-treated enolase, actin and tubulin but not calmodulin. Phosphorylation specificity of HPK40 was investigated using over a hundred peptidic structures. HPK40 is not related to the 'src' family and does not phosphorylate efficiently either the tetrapeptide NEYT derived from the pp60src autophosphorylation domain or the corresponding peptide RRsrc, RRLIED-NEYTARG. VALYDYESR from the SH3 domain of pp60c-src is recognized as a substrate with a high phosphorylation level. DEDYIQD, derived from the phosvitin/casein kinase II, was also highly phosphorylated. In order to determine the minimal recognition sequence of HPK40, the phosphorylation of about 60 dito tetrapeptides was investigated. Some of the tetrapeptides, such as *EEYE and NEYE, were well phosphorylated. Even some tripeptides, such as EYE, DYM, TYS and KYE, were recognized by HPK40, while none of the tested dipeptides was recognized as substrate. Sequences of peptides from DRVYHPF (angiotensin), LEEEEEAYGWMDF (minigastrin) and QEEYSAM (from H-ras1) were examined as substrates. The presence of one or several acidic residues on the N alpha-side of tyrosine residue was identified as the only apparently favorable determinant.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Use of hydrophilic interaction chromatography for the study of tyrosine protein kinase specificity

A new HPLC method has been developed to assay tyrosine protein kinase activity. Using hydrophilic interaction chromatography, it is possible to resolve the four components of the incubation medium: substrate peptide, [32P]phosphorylated peptide, unreacted [gamma-32P]ATP, and 32P-labelled inorganic phosphate. ATP interacts so strongly with the stationary phase material that it can be removed selectively from the incubation medium with solid-phase extraction cartridges packed with the same type of material. The three remaining components of interest can then be resolved by reversed-phase or hydrophilic interaction HPLC. This procedure permits the evaluation of almost every type of peptide as a substrate of tyrosine protein kinase.

Specificity determinants for tyrosine protein kinase. A study with recombinant hirudin mutants

Hirudin, the powerful anticoagulant agent of leech (Hirudo medicinalis) saliva, was readily phosphorylated by two spleen tyrosine protein kinases (TPK-IIB and TPK-III) at Tyr63 with Km values of 238 microM and 74 microM, respectively. The synthetic tridecapeptide DGDFEEIPEEYLQ, corresponding to the hirudin 53-65 C-terminal fragment, was phosphorylated even more efficiently than hirudin itself. Four hirudin mutants, in which one or more of the glutamic acids at positions 57, 58, 61 and 62 have been replaced by glutamines, were poorer substrates than hirudin. The mutant in which all four glutamates were substituted, [Gln57,58,61,62]hirudin, was virtually not phosphorylated by either TPK-IIB and TPK-III. Substitution of Glu57 and Glu58 was less deleterious than substitution of the two glutamic acids adjacent to Tyr63: [Gln61,62]hirudin exhibited a 20-fold lower phosphorylation efficiency with TPK-IIB. With TPK-III, however, the Km value of [Gln61,62]hirudin was slightly lower, while the Vmax decreased sixfold. The substitution of Glu62 alone was also more detrimental with TPK-IIB than with TPK-III. The behaviour of a third spleen TPK, named lyn TPK-I and belonging to the src family, was markedly different in that it did not phosphorylate hirudin but exhibited significant activity towards [Gln57,58,61,62]hirudin. Taken together, these data confirm and extend with a protein substrate the results obtained with short model peptides which indicated the stringent substrate requirements of TPK-IIB (and of TPK-III to a lesser extent) for N-terminal acidic residues. In contrast, such residues are deleterious with lyn TPK-I. These observations also support the concept that tyrosine protein kinases recognize specificity determinants situated in the vicinity of the target residue rather than requiring higher-order structural features.

Stimulation by NaCl, polylysine and heparin of two forms of spleen tyrosine protein kinase immunologically related with the protein expressed by lyn oncogene

The previously isolated spleen tyrosine protein kinase, conventionally termed TPK-IIA, displaying activation by either positively or negatively charged polyelectrolytes has been further characterized. TPK-IIA is immunologically related with the tyrosine protein kinase encoded by the lyn gene, a member of src subfamily and is dramatically activated by very high NaCl concentration. The stimulatory effects of NaCl and polylysine, which are not additive, are accounted for by increased Vmax values, the Km being virtually unchanged, suggesting that both effectors probably interact with the same site(s). Stimulation of TPK-IIA by heparin appears to be partially additive to that promoted by NaCl and possibly occurring through a different mechanism. The NaCl activatory effect correlates with the electrolytic nature of synthetic peptides used as substrates, being much more consistent with neutral peptides as compared with acidic ones. Of the other three spleen tyrosine protein kinases, TPK-I shows similar biochemical and immunological features, suggestive of close relatedness with TPK-IIA, while TPK-IIB and TPK-III are neither related with the lyn protein nor with the products of three other oncogenes of the src subfamily, namely lck, hck and fyn.

Different specificities of spleen tyrosine protein kinases for synthetic peptide substrates

20 synthetic peptides, each of which includes a tyrosyl residue flanked by either neutral or acidic amino acids in different proportions and at variable positions, have been employed as model substrates for investigation of the site specificity of three tyrosine protein kinases previously isolated from spleen [Brunati, A. M. & Pinna, L. A. (1988) Eur. J. Biochem. 172, 451-457] and conventionally termed TPK-I, TPK-IIB and TPK-III. Comparison of the phosphorylation efficiencies shows that each tyrosine protein kinase is considerably different from the others in both the stringency and the nature of its specificity determinants. By considering, in particular, the kinetic constants obtained with the pentapeptides AAYAA, EEYAA, AEYAA, EAYAA, with the tetrapeptides AYAA and EYAA and with the tripeptides AYA and EYA, it turns out that N-terminal acidic residue(s) are only essential with TPK-IIB for efficient phosphorylation with multiple residues displaying a synergistic effect. The very similar Km (130 microM) but 14-fold-different Vmax values with YEEEEE vs. EEEEEY indicate that an N-terminal rather than C-terminal location of acidic residues is required for a high phosphorylation rate with, though not for binding to TPK-IIB. Acidic residues decrease the phosphorylation rate with TPK-I, a kinase related to the src family which is immunologically indistinguishable from the lyn TPK; they are nearly ineffective, however, with TPK-III, the least specific of the tyrosine protein kinases, which exhibits appreciable activity toward tripeptides and dipeptides like GAY and AY which are not significantly affected by TPK-I and TPK-IIB. While the peptide substrate specificity of TPK-I is similar to that of TPK-IIA, a spleen tyrosine protein kinase previously considered [Brunati, A. M., Marchiori, F., Ruzza, P., Calderan, A., Borin, G. & Pinna, L. A. (1989) FEBS Lett. 254, 145-149], the remarkable requirement of TPK-IIB alone for acidic peptides may suggest the involvement of this enzyme, which is also unique in its failure to autophosphorylate, in the phosphorylation of the highly conserved and quite acidic phosphoacceptor sites of the src family protein kinases.

Assay of tyrosine protein kinase activity from HL-60 by high-performance liquid chromatography for specificity studies

Using a partially purified HL-60 tyrosine protein kinase, we designed a new HPLC method for the measurement of tyrosylphosphorylation of angiotensin II. The present method uses reversed-phase chromatography and elution involving an acetonitrile gradient containing the counterion tetrabutylammonium phosphate. The peptide substrate, [gamma-32P]ATP, the cosubstrate, and 32P-labeled phosphorylated peptides were quantified online by measuring the Cerenkov effect. Injections, separation, and analysis were performed automatically. Furthermore, the method permits a direct visualization of peptide substrate phosphorylation and has a potentially universal application; i.e., it is usable with any kind of peptide in a given range of hydrophobicity. This assay was designed for specificity studies, which are of major importance at the molecular level, in order to understand active site topology and the biophysical requirements of tyrosine protein kinases. As examples, data on chromatography separations of angiotensin II analogs (five to ten amino acids in length) are presented, as well as for other peptide substrates such as RR-src, the pp60src autophosphorylation site-derived peptide, and minigastrin. We adapted our experimental conditions to accommodate crude extracts from HL-60 cells. Preliminary experiments clearly indicated that other biological sources can be used. Despite the existence of numerous methods published in the literature for the measurement of kinase activities, the method presented herein is the only one to the authors' knowledge that can be used in and has been assessed for specificity studies. Peptides do not require particular features such as charged residues (i.e., arginine) to be analyzed.

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.