Identification of cytosolic protein tyrosine kinases of human prostate by renaturation after SDS/PAGE

What Room for Two-Dimensional Gel-Based Proteomics in a Shotgun Proteomics World?

Two-dimensional gel electrophoresis was instrumental in the birth of proteomics in the late 1980s. However, it is now often considered as an outdated technique for proteomics—a thing of the past. Although this opinion may be true for some biological questions, e.g., when analysis depth is of critical importance, for many others, two-dimensional gel electrophoresis-based proteomics still has a lot to offer. This is because of its robustness, its ability to separate proteoforms, and its easy interface with many powerful biochemistry techniques (including western blotting). This paper reviews where and why two-dimensional gel electrophoresis-based proteomics can still be profitably used. It emerges that, rather than being a thing of the past, two-dimensional gel electrophoresis-based proteomics is still highly valuable for many studies. Thus, its use cannot be dismissed on simple fashion arguments and, as usual, in science, the tree is to be judged by the fruit.

Changes of protein tyrosine phosphorylation in third instar larval integument of the Mediterranean fruit fly, Ceratitis capitata

Developmental analysis of the tyrosine protein phosphorylation levels in larval integument and partial characterization of the endogenous protein tyrosine kinase activity (PTK) in Ceratitis capitata are described in this study. Larval integument contains high levels of PTK activity at the early stages of the third instar, which progressively declines to low levels in the white pupal stage. An integumental 90-kDa polypeptide was identified to have prominent endogenous PTK activity and follow a similar developmental pattern. The major integumental phosphotyrosine-containing polypeptides have apparent molecular weights of 30, 41, 44, 46, and 54 kDa, respectively. Polypeptides with molecular weights of 62 and 73 kDa were identified as Ser/Thr-containing phosphoproteins and were shown to exhibit high levels of phosphorylation at the middle stage of larval development. These differences are likely to be due to the higher activation state of the protein tyrosine kinase(s) at the early stages of larval development.

Capacitation is associated with tyrosine phosphorylation and tyrosine kinase-like activity of pig sperm proteins

Capacitation represents the final maturational steps that render mammalian sperm competent to fertilize, either in vivo or in vitro. Capacitation is defined as a series of events that enables sperm to bind the oocyte and undergo the acrosome reaction in response to the zona pellucida. Although the molecular mechanisms involved are not fully understood, sperm protein phosphorylation is associated with capacitation. The hypothesis of this study is that protein tyrosine phosphorylation and kinase activity mediate capacitation of porcine sperm. Fresh sperm were incubated in noncapacitating or capacitating media for various times. Proteins were extracted with SDS, subjected to SDS-PAGE, and immunoblotted with an antiphosphotyrosine antibody. An M(r) 32 000 tyrosine-phosphorylated protein (designated as p32) appeared only when the sperm were incubated in capacitating medium and concomitant with capacitation as assessed by the ionophore-induced acrosome reaction. The p32 was soluble in Triton X-100. Fractionation of sperm proteins with Triton X-114 demonstrated that after capacitation, this tyrosine phosphoprotein is located in both the cytosol and the membrane. Enzyme renaturation of sperm proteins was conducted in gels with or without either poly glu:tyr (a tyrosine kinase substrate) or kemptide (a protein kinase A substrate). An M(r) 32 000 enzyme with kinase behavior was observed in all gels but was preferentially phosphorylated on tyrosine, as assessed by phosphorimagery and by thin layer chromotography to identify the phosphoamino acids. Indirect immunolocalization showed that the phosphotyrosine residues redistribute to the acrosome during capacitation, which is an appropriate location for a protein involved in the acquisition of fertility.

The detection of enzyme activity following sodium dodecyl sulfate-polyacrylamide gel electrophoresis

More than a hundred different enzymes impinging on aspects of cell function ranging from carbohydrate and lipid metabolism to signal transduction and gene expression to biomolecule degradation have been detected by the assay of their enzymatic activities following SDS-PAGE. The strategies by which this has been accomplished are as varied as the enzymes themselves and offer testimony to the creativeness and ingenuity of life scientists. Assay of enzyme activity following SDS-PAGE is well adapted to identifying the source of catalytic activity in a heterogeneous protein mixture or a heterooligomeric protein (20), or determining if multiple catalytic activities reside in a single polypeptide (60). The alliance of versatile enzyme assay techniques with the molecular resolution of SDS-PAGE offers a powerful means for meeting the increasing demand for the high-throughput screening arising from protein engineering, combinatorial chemistry, and functional genomics.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes an Ah receptor-dependent and ARNT-independent increase in membrane levels and activity of p60(Src)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to affect various cellular activities including growth factor signal transduction, hormone responses, and cell differentiation. The purpose of this study was to examine more closely the very early effects of TCDD on protein tyrosine kinase activity, specifically p60(Src). We found that TCDD causes rapid changes in the plasma-microsomal membrane levels and activity of p60(Src) in Hepa 1c1c7, Hepa c4 cells, and SR3Y1 cells, a p60(v-Src) overexpressing cell line. Such cellular changes occur within 30 minutes after 10 nM TCDD treatment, as measured by Western blot analysis. TCDD's ability to increase p60(Src) levels was found to be: (1) dose-dependent, with an estimated EC(50) between 10(-10) and 10(-11) M TCDD; (2) Ah receptor (AhR)-dependent, since TCDD's effect was blocked by co-administration with 1 μM α-naphthoflavone, an AhR antagonist; and interestingly (3) ARNT-independent, since TCDD's effect was observed in Hepa c4 cells, an ARNT(-) mutant cell line. Since ARNT is a heterodimerization partner of the AhR required for binding of the ligand-activated AhR to dioxin-responsive elements on DNA in the nucleus to transactivate genes controlled by the AhR, an alternative mechanism for TCDD's action is discussed which does not require ARNT. Along with increased membrane levels of p60(Src), we observed a corresponding increase in the activity of a 60 kDa protein tyrosine kinase using two different kinase detection assays. This effect of TCDD was also found to be AhR-dependent, ARNT-independent, and independent of de novo protein synthesis since cycloheximide was unable to completely abolish TCDD's effect. The present findings provide a potentially important mechanism by which TCDD can alter cell growth and differentiation.

Estradiol activates p60src, p53/56lyn and renatured p50/55 protein tyrosine kinases in the dog prostate

Protein tyrosine kinases (PTKs) are key enzymes implicated in signal transduction pathways regulated by growth factors (GFs). We have previously shown by immunohistochemistry that the level of phosphotyrosine (pY) proteins is increased in prostatic basal epithelial cells following estrogen treatment in castrated dogs. In this study, we investigated if this treatment increases the level and distribution of prostatic PTK activity, and more specifically, if it alters the expression and/or activity of the Src family members p60src and p53/56lyn. Prostates from normal and hyperplastic dog prostates, as well as those from castrated dogs treated with androgens, were also examined. Only the glands obtained from estrogen-treated dogs had a significantly increased total and specific PTK activity, observed uniquely in the particulate extract, as compared to the other types of prostates studied. In addition, this increased activity was correlated upon gel filtration chromatography with the presence of an additional peak of activity with an apparent molecular weight of 130 kDa, which was absent in other prostate fractions presenting only 50 kDa peaks. Using antibodies, we demonstrate that active p60src and pp53/56lyn kinases accounted for 81% of the activity in this 130 kDa peak. On the other hand, in situ renaturation also revealed the presence of still uncharacterized 50/55 kDa PTKs in the 130 kDa peak. Altogether, these findings raise the possibility that these PTKs contribute to the transmission of mitogenic signals originating directly or indirectly from estrogen stimulation of the basal cell layer of the prostate.

Mitogen-activated protein kinase activity during goat oocyte maturation and the acquisition of meiotic competence

Changes in MPF and MAPK activities during meiotic maturation of goat oocytes were investigated. Detection of MPF activity occurred concomitantly with GVBD, increased at MI, decreased during anaphase-telophase I transition, and increased thereafter in MII oocytes. The appearance of MAPK activity was delayed compared to MPF activity. MAPK activity increased after GVBD and persisted during the MI-MII transition. Whether MAPK was implicated in goat oocyte meiotic competence was also investigated by using oocytes from different follicle size categories that arrest at specific stages of the maturation process (GV, GVBD, MI, and MII). Results indicate that the ability of goat oocytes to resume meiosis is not directly related to the presence of Erk2. The ability to phosphorylate MAPK is acquired by the oocyte during follicular growth after the ability to resume meiosis. GVBD-arrested oocytes exhibited a high level of MPF activity after 27 hr of culture. However, 28% of oocytes from this group contained inactive MAPK, and 72% exhibited high MAPK activity. In addition, 29% of GVBD-arrested oocytes contained a residual interphasic network without recruitment of microtubules around the condensed chromosomes; 71% of GVBD-arrested oocytes displayed recruitment of microtubules near the condensed chromosomes and contained asters of microtubules distributed throughout the cytoplasm. These results indicate that oocytes arrested at GVBD were not exactly at the same point in the meiotic cell cycle progression, and suggest that MAPK could be implicated in the regulation of microtubule organization. The data presented here suggest that in goat oocytes, MAPK is not implicated in the early events of meiosis resumption, but rather in post-GVBD events such as spindle formation and MII arrest.

Radiation inactivation and in situ renaturation of protein tyrosine kinases reveal a major 50-kDa enzyme as part of a membrane complex present in dividing but not in resting prostatic epithelial cells

Because protein tyrosine kinases play a crucial role in the regulation of cell division and carcinogenesis, we have herein measured such enzyme activities (specific activity and subcellular distribution) and compared their characteristics with respect to hydrodynamic properties and radiation inactivation sizes as well as renaturation after electrophoresis in denaturing conditions in canine prostatic epithelial cells either in a resting (freshly isolated) or in a dividing (cultured cells) state. In quiescent cells, most protein tyrosine kinase activity was expressed by soluble proteins with a Stokes' radius (Rs) of 3.05 nm, a sedimentation coefficient (S20,w) of 4.0 S, and a molecular mass of 50 kDa. By contrast, in dividing cells (three days in primary culture), the specific activity was higher and the enzyme was mainly membrane bound. The use of a detergent (Triton X-100) allowed the extraction of most of that enzyme; its partial specific volume, S20,w and Rs were then 0.883 cm3/g, 4.0 S, and 5.6 nm, respectively, hence yielding a molecular mass of 215 kDa, which decreased to 125-145 kDa when corrected for detergent binding. Probing these chromatography-peak fractions, 50 kDa from cytosol of resting cells and 215 kDa from membrane extracts of dividing cells, with a phosphotyrosine antibody following their incubation with ATP and electrophoresis in denaturing conditions revealed the presence of a common 50-kDa phosphotyrosylated protein along with three other bands (130, 75, and 40 kDa) in the high-Mr peak of enzyme. However, the radiation inactivation size for protein tyrosine kinases expressed in both resting and dividing cells were similar, 47.2 +/- 8.7 and 44.5 +/- 6.1 kDa, respectively. Furthermore, by renaturation after electrophoresis in denaturing conditions, major protein tyrosine kinase polypeptides of 50 kDa were identified in both cell populations. Taken together, these results indicate that, in dividing prostatic epithelial cells, membrane-bound protein tyrosine kinases of low molecular weight with properties similar to those of monomeric soluble forms present in quiescent cells are part of high-molecular weight complexes. This activation process may be critical for hormone-independent proliferation of prostatic epithelial cells.

Activation of a serine/threonine kinase signaling pathway by transforming growth factor type beta

Transforming growth factor type beta (TGF-beta) is a multifunctional factor that regulates proliferation and differentiation of many cell types. TGF-beta mediates its effects by binding to and activating cell surface receptors that possess serine/threonine kinase activity. However, the intracellular signaling pathways through which TGF-beta receptors act remain largely unknown. Here we show that TGF-beta activates a 78-kDa protein (p78) serine/threonine kinase as evidenced by an in-gel kinase assay. Ligand-induced activation of the kinase was near-maximal 5 min after TGF-beta addition to the cells and occurred exclusively on serine and threonine residues. This kinase is distinct from TGF-beta receptor type II, as well as several cytoplasmic serine/threonine kinases of similar size, including protein kinase C, Raf, mitogen-activated protein kinase kinase kinase, and ribosomal S6 kinase. Indeed, these kinases can be separated almost completely from p78 kinase by immunoprecipitation with specific antibodies. Furthermore, using different cell lines, we demonstrate that p78 kinase is activated only in cells for which TGF-beta can act as a growth inhibitory factor. These data raise the interesting possibility that protein serine/threonine kinases contribute to the intracellular relay of biological signals originating from receptor serine/threonine kinases such as the TGF-beta receptors.

Detection of phosphotyrosine in glutaraldehyde-crosslinked and alkali-treated phosphoproteins following their partial acid hydrolysis in gels

Soluble fractions and particulate extracts from human prostate, and extracts from rat-liver membranes were used as a source of kinases to phosphorylate endogenous proteins in the presence of gamma- 32P-labeled ATP. Histone was also added as a substrate in order to compare the direct partial acid hydrolysis of phosphoproteins in gels to an indirect procedure involving partial acid hydrolysis after extraction in sodium dodecyl sulfate followed by precipitation with acetone. These procedures led to recoveries of 32P-labeled material of 90% and 40%, respectively, with a similar proportion of radiolabeled phosphoamino acids. Several 32P-labeled phosphoproteins separated in gels were therefore directly HCl-hydrolyzed and their phosphoamino acids were quantitated either prior to, or after glutaraldehyde crosslinking, with and without alkali treatment. By preventing protein losses occurring in hot alkali, glutaraldehyde crosslinking increased by an average factor of 6.5 the 32P-labeled material available for phosphoamino-acid analyses. For eight phosphoproteins analyzed, the overall effect of combined glutaraldehyde and alkali treatments was a relative decrease in phosphoserine (up to 8-fold), with concomitant relative increases in phosphotyrosine and phosphothreonine (up to 62- and 6-fold, respectively). This method will especially be useful for the detection of pTyr, a less abundant phosphoamino acid, in proteins which suffer from poor transfer efficiency in Western blot, are weakly antigenic towards anti-phosphotyrosine antibodies, can hardly be extracted from a gel and for identification of protein tyrosine kinases renatured in gels.

Solid-phase synthesis of (tyrosyl-alanyl-glutamyl)n by segment condensation

(Tyr-Ala-Glu)n, n = 1-9, were synthesized by segment condensation using the Fmoc/tert-butyl protection strategy and solid-phase techniques. The C-terminal residue was coupled to the resin and the peptides were built out by adding Fmoc-Glu(O-t-Bu)-Tyr(t-Bu)-Ala-OH units. When the desired lengths were reached the peptides were capped with Fmoc-Tyr(t-Bu)-Ala-OH units. Fmoc-Tyr(t-Bu)-Ala-OH and Fmoc-Glu(O-t-Bu)-Tyr(t-Bu)-Ala-OH were synthesized in aqueous solution by the successive addition of N-hydroxysuccinimide esters of Fmoc-Tyr(t-Bu) and Fmoc-Glu(O-t-Bu) to the growing chain. Neither sequential amino acid addition or segment condensation techniques were successful on polystyrene supports. However, the segment condensations were highly successful on kieselguhr-supported polydimethylacrylamide based resins. (Tyr-Ala-Glu)n, n = 1-9, were tested as inhibitors of the protein tyrosine kinase, pp60c-src. Inhibition, as measured by IC50 values, increased with increasing size of the peptide.