Trimer carboxyl propeptide of collagen I produced by mature osteoblasts is chemotactic for endothelial cells

During the second phase of osteogenesis in vitro, rat osteoblasts secrete inducer(s) of chemotaxis and chemoinvasion of endothelial and tumor cells. We report here the characterization and purification from mature osteoblast conditioned medium of the agent chemotactic for endothelial cells. The chemoactive conditioned medium specifically induces directional migration of endothelial cells, not affecting the expression and activation of gelatinases, cell proliferation, and scattering. Directional migration induced in endothelial cells by conditioned medium from osteoblasts is inhibited by pertussis toxin, by blocking antibodies to integrins alpha(1), beta(1), and beta(3), and by antibodies to metalloproteinase 2 and 9. The biologically active purified protein has two sequences, coincident with the amino-terminal amino acids, respectively, of the alpha(1) and of the alpha(2) carboxyl propeptides of type I collagen, as physiologically produced by procollagen C proteinase. Antibodies to type I collagen and to the carboxyl terminus of alpha(1) or alpha(2) chains inhibit chemotaxis. The chemoattractant is the propeptide trimer carboxyl-terminal to type I collagen, and its activity is lost upon reduction. These data illustrate a previously unknown function for the carboxyl-terminal trimer, possibly relevant in promoting endothelial cell migration and vascularization of tissues producing collagen type I.

Mitochondrial function in cell wall glycoprotein synthesis in Saccharomyces cerevisiae NCYC 625 (Wild type) and [rho(0)] mutants

We studied phosphopeptidomannans (PPMs) of two Saccharomyces cerevisiae NCYC 625 strains (S. diastaticus): a wild type strain grown aerobically, anaerobically, and in the presence of antimycin and a [rho(0)] mutant grown aerobically and anaerobically. The aerobic wild-type cultures were highly flocculent, but all others were weakly flocculent. Ligands implicated in flocculation of mutants or antimycin-treated cells were not aggregated as much by concanavalin A as were those of the wild type. The [rho(0)] mutants and antimycin-treated cells differ from the wild type in PPM composition and invertase, acid phosphatase, and glucoamylase activities. PPMs extracted from different cells differ in the protein but not in the glycosidic moiety. The PPMs were less stable in mitochondrion-deficient cells than in wild-type cells grown aerobically, and this difference may be attributable to defective mitochondrial function during cell wall synthesis. The reduced flocculation of cells grown in the presence of antimycin, under anaerobiosis, or carrying a [rho(0)] mutation may be the consequence of alterations of PPM structures which are the ligands of lectins, both involved in this cell-cell recognition phenomenon. These respiratory chain alterations also affect peripheral, biologically active glycoproteins such as extracellular enzymes and peripheral PPMs.

HER-2/c-erbB2 is phosphorylated by calmodulin-dependent protein kinase II on a single site in the cytoplasmic tail at threonine-1172

Calmodulin-dependent protein kinase II (Cam kinase II) is known to desensitise epidermal growth factor receptor (HER-1) tyrosine kinase activity by a process involving phosphorylation at serines 1046/47 in the cytoplasmic tail. We have developed an experimental system to investigate phosphorylation of the related HER-2/c-erbB2 proto-oncogene utilising purified Cam kinase II and recombinant glutathione-S-transferase (GST) fusion proteins. The cDNA for rat Cam kinase II-alpha was transfected into human embryonic kidney (HEK) 293 fibroblasts and the expressed protein purified to homogeneity by calmodulin-agarose affinity chromatography. A GST fusion protein comprising residues 1126-1255 of HER-2 was phosphorylated by purified Cam kinase II, in contrast to a GST protein comprising residues 1005-1125. Phosphoamino-acid analysis and site-directed mutagenesis indicated that HER-2 was phosphorylated on a single site at threonine-1172 which resides within a consensus Cam kinase II phosphorylation site (RAKT). HER-2 (threonine-1172-alanine), in the form of a ligand-inducible chimaera HER-1/2, was co-transfected into HEK-293 fibroblasts with a constitutively active form of Cam kinase II, followed by in vivo labelling of these cells with 32 P-orthophosphate. Immunoprecipitation of ligand-activated receptors followed by two-dimensional phosphopeptide mapping indicated that threonine-1172 in HER-2 is a newly identified in vivo site which can be hyper-phosphorylated by constitutively active Cam kinase II. In addition, when over-expressed in HEK-293 fibroblasts, HER-1/2 (threonine-1172-alanine) showed a defect in desensitisation and underwent a more sustained EGF-induced receptor autophosphorylation compared to wild-type HER-1/2.

Kinetic mechanisms of the forward and reverse pp60c-src tyrosine kinase reactions

The kinetic mechanism of the pp60c-src tyrosine kinase (src TK) reaction was investigated in the forward and reverse directions. In the forward direction, initial velocities obtained by varying ATP and the peptide (FGE)3Y(GEF)2GD indicated a sequential addition of the two substrates. The peptide analog, (FGE)3F(GEF)2GD, was a competitive inhibitor versus the peptide substrate and a noncompetitive inhibitor versus MgATP. Interestingly, the tyrosine hydroxyl group imparts only a 6-fold increase in binding. AMP-PCP was a competitive inhibitor versus MgATP and a noncompetitive inhibitor versus the peptide substrate. These results prove that the addition of substrates is random. Furthermore, there appears to be little binding synergy as the KiMgATP approximately equal to 2.4KmMgATP. The phosphorylated peptide (FGE)3-pY-(GEF)2GD was a competitive inhibitor versus peptide and a noncompetitive inhibitor against MgATP, suggesting that a dead end complex can form between MgATP, the phosphorylated peptide product, and the enzyme. The reverse reaction was investigated by varying ADP and the phosphopeptide. (FGE)3-pY-(GEF)2GD. The initial velocity pattern was indicative of a sequential mechanism. There was even less binding synergy in the reverse direction as the KiMgADP approximately equal to 1.4KmMgADP. AMP-CP was a competitive inhibitor versus MgADP and a noncompetitive inhibitor versus the phosphopeptide. (FGE)3F(GEF)2GD was a competitive inhibitor versus the phosphopeptide and a noncompetitive inhibitor versus MgADP. These data prove that addition of the substrates in the reverse direction is random. (FGE)3Y(GEF)2GD was a competitive inhibitor against peptide substrate and a noncompetitive inhibitor against MgADP; therefore a dead end complex can form between MgADP, (FGE)3Y(GEF)2GD, and the enzyme. These results indicate that the src TK reaction follows a sequential bi-biequilibrium random mechanism in both directions, with dead end complexes forming when either MgATP and (FGE)3-pY-(GEF)2GD or MgADP and (FGE)3Y(GEF)2GD bind to the enzyme. The kinetic constants determined from the forward and reverse reactions were used in the Haldane equation to determine a K(eq) constant for the forward reaction of 10.1, corresponding to a delta G of -1.4 kcal/mol. This further confirms that the O-P bond of phosphotyrosine is similar in energy to that of the gamma-phosphoryl of MgATP.

Functional comparison of native and recombinant human salivary histatin 1

Histatin 1 is a histidine-rich phosphoprotein present in human parotid saliva that possesses candidacidal activity and functions in mineralization by adsorbing to hydroxyapatite. The objective of the present study was to develop a system for recombinant production of histatin 1 and to examine the role of phosphorylation in the functional activities of this molecule. Native histatin 1 (containing a phosphoserine at residue 2) was purified from parotid saliva, whereas a bacterial expression system was used to produce a recombinant form of histatin 1 (re-Hst1) that lacked phosphorylated serine. Histatin 1 cDNA was inserted into the vector pGEX-3X, which expresses foreign genes as soluble fusion proteins attached to the carboxyl-terminus of glutathione S-transferase (GST). The GST/re-Hst1 fusion protein was isolated from cell lysates by affinity chromatography on glutathione (GSH)-Sepharose and digested with cyanogen bromide to separate re-Hst1 from the GST fusion partner. The digest was subjected to reversed-phase high-performance liquid chromatography on a C18 column, and re-Hst1 was eluted as a well-defined peak. The yield of re-Hst1 was 4 mg/L of bacterial culture. Amino-terminal sequencing and amino acid analysis confirmed the final product as re-Hst1. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that native histatin 1 and re-Hst1 had the same apparent molecular weights, while cationic PAGE showed that re-Hst1 was more basic. Phosphate analysis indicated 1 mol phosphate/mol of native histatin 1, while re-Hst1 lacked any detectable phosphate. Re-Hst1 demonstrated candidacidal activity comparable to that of native histatin 1, but displayed substantially lower binding to hydroxyapatite. These results show that phosphorylation of histatin 1 at residue 2 contributes significantly to its ability to bind to hydroxyapatite.

Chemical characterization of bioactive peptides from in vivo digests of casein

The in vivo formation of biologically active caseinopeptides was studied. It was proved that bioactive peptides were released in the small intestine of minipigs in the course of luminal digestion of diets containing bovine casein. An opioid peptide and a phosphopeptide were isolated from jejunal chyme and were chemically characterized. The opioid peptide has been identified as a fragment of beta-casein (60-70). This peptide, named beta-casomorphin-11, displayed substantial opioid activity in an opiate receptor-binding assay. The caseinophosphopeptide has been shown to be a fragment of alpha s1-casein (66-74). Casein-derived phosphopeptides exhibit a potent ability to form soluble complexes with Ca and trace elements. Evidence exists that casomorphins and caseinophosphopeptides participate in the regulation of nutrient entry.

Effects of subinhibitory dose of amphotericin B on cell wall biosynthesis in Candida albicans

Subinhibitory doses of amphotericin B in the culture medium of Candida albicans modified yeast cell wall synthesis. Analysis of isolated cell walls showed a decrease in mannose and an increase in amino acid and glucosamine levels. After fractionation of the cell wall by ethylenediamine or pronase digestion, study of the fractions corroborated an outer phosphopeptidomannan decrease and an enrichment of matrix constituents. Determination of the amount of chitin showed stimulation of synthesis of this amino polysaccharide in yeasts grown in the presence of amphotericin B. Decrease in phosphopeptidomannans and high production of other cell wall constituents are probably consequences of modification of the lipidic environment of membrane-bound enzymes by the antifungal polyene action.

Analysis of desmin and vimentin phosphopeptides in cultured avian myogenic cells and their modulation by 8-bromo-adenosine 3',5'-cyclic monophosphate

The intermediate filament proteins desmin and vimentin are two of the major 32P phosphate acceptors in chicken myotubes differentiating in tissue culture. Analysis of the desmin and vimentin phosphopeptides by two-dimensional tryptic peptide mapping shows that both proteins are phosphorylated at multiple sites, giving rise to 5 phosphopeptides in desmin and as many as 11 in vimentin. Addition of the cAMP analogue 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) to the culture medium of mature (8-day-old) myotubes results in a 2- to 3-fold increase in PO4 incorporation into desmin and vimentin. Two-dimensional tryptic analysis of desmin and vimentin from 8-BrcAMP-treated myotubes shows increased 32PO4 incorporation into a subset of the phosphopeptides observed in control cells. Comparison of phosphopeptides from the two proteins shows the presence of at least three comigrating peptides. All three comigrating peptides exhibit cAMP-dependent increases in 32PO4 incorporation in vimentin, while only two of the three exhibit 8-BrcAMP-dependent responses in desmin. While these peptides are the only two that are sensitive to 8-BrcAMP in desmin, vimentin contains additional peptides that exhibit increased 32PO4 incorporation in response to 8-BrcAMP. This result suggests the existence of both common and distinct phosphorylation sites between desmin and vimentin that may be differentially regulated by cAMP. Thus, desmin and vimentin, even though structurally related, may be capable of responding differently to physiological stimuli.

Epstein-Barr virus-induced proteins. IV. Characterization of an EBV-associated phosphopolypeptide

Cells of the Epstein--Barr virus (EBV) non-producing lines NC37 and Raji were induced by the tumour promoter TPA and were labelled with 32P. The analysis by immunoprecipitation with human VCA+EA+ sera revealed that a major phosphopolypeptide with a mol. wt. of 58 000 was specifically precipitated. In addition, a phosphopolypeptide of the same size was the dominant phosphopolypeptide detected in EBV-producing B95-8 and P3HR-1 cells as well as in P3HR-1-superinfected NC37 cells. This phosphopolypeptide seemed to be EBV-specific, because it was not detectable in TPA-treated, but EBV genome-negative, Ramos and BJAB cells. Synthesis of this phosphopolypeptide was inhibited in TPA-treated NC37 cells by treatment with Ara-C. VCA+EA+ sera were found to be more immunoreactive with this phosphopolypeptide than VCA+EA- or EBNA+ sera. Based on these results this phosphopolypeptide may have some immunological relatedness to the EBV-specific early antigen (EA) complex defined by immunofluorescence.

Phosphopeptides and soluble calcium in the small intestine of rats given a casein diet

1. Semi-synthetic diets containing 200 g protein/kg were meal-fed for 1.5 h to groups of rats. The contents of the whole small intestinal tract were collected and the amount of soluble calcium was determined. 2. In the rats given 200 g casein/kg diet, formation of a fraction containing macrophosphopeptide in the small intestine was confirmed by gelfitration of the intestinal contents on Sephadex G-25. However, this macrophosphopeptide fraction was not found when casein alone was fed. 3. In the intestinal contents at 2.5 h after ingestion, the amounts of both soluble Ca and phosphorus were significantly higher in rats fed the casein diet than in those fed diets containing egg albumin, isolated soya-bean protein or an amino acid mixture. However, the amount of insoluble Ca was least in rats fed the casein diet.

Regulation of plasma membrane protein phosphorylation in two mammalian cell types

The appreciation of protein phosphorylation as a ubiquitous mechanism for the post-translational control of protein function has drawn our attention to the phosphorylation of plasma membrane proteins. We have studied this phenomenon in the human erythrocyte and rat adipocyte, and have observed several features, common to the two systems, which may be of general significance. In examining protein phosphorylation in intact cells incubated with 32Pi, it is evident that the 32P-polypeptides of the plasma membrane are among the most highly labelled species in the cell, despite their minor contribution to overall protein content. The addition of epinephrine (to adipocytes) or cAMP (to erythrocytes) increases the phosphorylation of certain peptides, whereas others are unaffected. The protein kinases mediating these phosphorylations are present in the plasma membrane as isolated, and can be divided into two groups--cAMP dependent and cAMP independent. These two classes of kinase differ markedly in their substrate specificity toward endogenous and exogenous polypeptide substrates. Two classes of protein kinases with similar properties can be detected in the cytoplasm. The relationship between the membrane-bound and cytoplasmic enzymes is uncertain. The potential roles of the plasma membrane cAMP dependent protein kinases are evident from the diverse effects of cAMP on surface properties; however, the prevalence of plasma membrane proteins phosphorylated via cAMP independent pathways is striking. Thus, elucidation of the regulatory properties of the plasma membrane cAMP independent protein kinases may give new insight into the control of a variety of surface phenomena not mediated by cAMP.