Basal phosphorylation of cyclic AMP-regulated phosphoproteins in intact S49 mouse lymphoma cells.
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ABSTRACT:
SUBMITTER: Steinberg RA
PROVIDER: S-EPMC1144931 | biostudies-other | 1985 May
REPOSITORIES: biostudies-other
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Project description:Protein phosphorylation is a ubiquitous and critical post-translational modification (PTM) involved in numerous cellular processes. Mass spectrometry (MS)-based proteomics has emerged as the preferred technology for protein identification, characterization, and quantification. Whereas ionization/detection efficiency of peptides in electrospray ionization (ESI)-MS are markedly influenced by the presence of phosphorylation, the physicochemical properties of intact proteins are assumed not to vary significantly due to the relatively smaller modification on large intact proteins. Thus, the ionization/detection efficiency of intact phosphoprotein is hypothesized not to alter appreciably for subsequent MS quantification. However, this hypothesis has never been rigorously tested. Herein, we systematically investigated the impact of phosphorylation on ESI-MS quantification of mono- and multiply phosphorylated proteins. We verified that a single phosphorylation did not appreciably affect the ESI-MS quantification of phosphoproteins as demonstrated in the enigma homolog isoform 2 (28 kDa) with monophosphorylation. Moreover, different ionization and desolvation parameters did not impact phosphoprotein quantification. In contrast to monophosphorylation, multiphosphorylation noticeably affected ESI-MS quantification of phosphoproteins likely due to differential ionization/detection efficiency between unphosphorylated and phosphorylated proteoforms as shown in the pentakis-phosphorylated ?-casein (24 kDa).
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Project description:Protein phosphorylation is a globally adopted and tightly controlled post-translational modification, and represents one of the most important molecular switching mechanisms that govern the entire spectrum of biological processes. In the central nervous system, it has been demonstrated that phosphorylation of key proteins mediating chromatin remodeling and gene transcription plays an important role controlling brain development, synaptogenesis, learning and memory. Many studies have focused on large scale identification of phosphopeptides in brain tissue. These studies have identified phosphorylation site specific motifs useful for predicting protein kinase substrates. In this study, we applied a previously developed quantitative approach, stable isotope labeling of amino acids in mammals (SILAM), to quantify changes in the phosphorylation of nuclear proteins between a postnatal day one (p1) and a p45 rat brain cortex. Using a 15N labeled rat brain as an internal standard, we quantified 705 phosphopeptides in the p1 cortex and 1477 phosphopeptides in the p45 cortex, which translates to 380 and 585 phosphoproteins in p1 and p45 cortex, respectively. Bioinformatic analysis of the differentially modified phosphoproteins revealed that phosphorylation is upregulated on multiple components of chromatin remodeling complexes in the p1 cortex. Taken together, we demonstrated for the first time the usefulness of employing stable isotope labeled rat tissue for global quantitative phosphorylation analysis.
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Project description:Effects on insulin release, cyclic AMP content and protein phosphorylation of agents modifying cyclic AMP levels have been tested in intact rat islets of Langerhans. Insulin release induced by glucose was potentiated by dibutyryl cyclic AMP, glucagon, cholera toxin and 3-isobutyl-1-methylxanthine (IBMX); the calmodulin antagonist trifluoperazine reversed these potentiatory effects. Inhibition by trifluoperazine of IBMX-potentiated release was, however, confined to concentrations of IBMX below 50 microM; higher concentrations, up to 1 mM, were resistant to inhibition by trifluoperazine. IBMX-potentiated insulin release was also inhibited by 2-deoxyadenosine, an inhibitor of adenylate cyclase. In the absence of glucose, IBMX at concentrations up to 1 mM did not stimulate insulin release and in the presence of 3.3 mM-glucose IBMX was effective only at a concentration of 1 mM; under the latter conditions trifluoperazine again did not inhibit insulin secretion. The maximum effect on insulin release was achieved with 25 microM-IBMX. Islet [cyclic AMP] was increased by IBMX, with the maximum rise occurring with 100 microM-IBMX. The increase in [cyclic AMP] elicited by IBMX was more rapid than that induced by cholera toxin. Trifluoperazine did not significantly affect islet cyclic AMP levels under any of the conditions tested. When islets were incubated with [32P]Pi, radioactivity was incorporated into islet ATP predominantly in the gamma-position. The rate of equilibration of label was dependent on medium Pi and glucose concentration and at optimal concentrations of these 100% equilibration of internal [32P]ATP with external [32P]Pi required a period of 3h. Radioactivity was incorporated into islet protein and, in response to an increase in islet [cyclic AMP], the major effect was on a protein of Mr 15 000 on sodium dodecyl sulphate/polyacrylamide gels. The extent of phosphorylation of the Mr-15 000 protein was correlated with the level of cyclic AMP: phosphorylation in response to IBMX was inhibited by 2-deoxyadenosine but not by trifluoperazine. Fractionation of islets suggested that the Mr-15 000 protein was of nuclear origin: the protein co-migrated with histone H3 on acetic acid/urea/Triton gels. In the islet cytosol a number of proteins were phosphorylated in response to elevation of islet [cyclic AMP]: the major species had Mr values of 18 000, 25 000, 34 000, 38 000 and 48 000. Culture of islets with IBMX increased the rate of [3H]-thymidine incorporation.(ABSTRACT TRUNCATED AT 400 WORDS)
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Project description:Nitric oxide (NO) generated by neuronal NO synthase (nNOS) initiates penile erection, but has not been thought to participate in the sustained erection required for normal sexual performance. We now show that cAMP-dependent phosphorylation of nNOS mediates erectile physiology, including sustained erection. nNOS is phosphorylated by cAMP-dependent protein kinase (PKA) at serine(S)1412. Electrical stimulation of the penile innervation increases S1412 phosphorylation that is blocked by PKA inhibitors but not by PI3-kinase/Akt inhibitors. Stimulation of cAMP formation by forskolin also activates nNOS phosphorylation. Sustained penile erection elicited by either intracavernous forskolin injection, or augmented by forskolin during cavernous nerve electrical stimulation, is prevented by the NOS inhibitor L-NAME or in nNOS-deleted mice. Thus, nNOS mediates both initiation and maintenance of penile erection, implying unique approaches for treating erectile dysfunction.
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Project description:The phosphorylation of any site on a given protein can affect its activity, degradation rate, ability to dock with other proteins or bind divalent cations, and/or its localization. These effects can operate within the same protein; in fact, multisite phosphorylation is a key mechanism for achieving signal integration in cells. Hence, knowing the overall phosphorylation signature of a protein is essential for understanding the "state" of a cell. However, current technologies to monitor the phosphorylation status of proteins are inefficient at determining the relative stoichiometries of phosphorylation at multiple sites. Here we report a new capability for comprehensive liquid chromatography mass spectrometry (LC/MS) analysis of intact phosphoproteins. The technology platform builds upon an integration of bottom-up and top-down approaches that is facilitated by intact protein reversed-phase (RP)LC concurrently coupled with Fourier transform ion cyclotron resonance (FTICR) MS and fraction collection. As the use of conventional RPLC systems for phosphopeptide identification has proven challenging due to the formation of metal ion complexes at various metal surfaces during LC/MS and ESI-MS analysis, we have developed a "metal-free" RPLC-ESI-MS platform for phosphoprotein characterization. This platform demonstrated a significant sensitivity enhancement for phosphorylated casein proteins enriched from a standard protein mixture and revealed the presence of over 20 casein isoforms arising from genetic variants with varying numbers of phosphorylation sites. The integrated workflow was also applied to an enriched yeast phosphoproteome to evaluate the feasibility of this strategy for characterizing complex biological systems and revealed approximately 16% of the detected yeast proteins to have multiple phosphorylation isoforms. The intact protein LC/MS platform for characterization of combinatorial post-translational modifications (PTMs), with special emphasis on multisite phosphorylation, holds great promise to significantly extend our understanding of the roles of multiple PTMs on signaling components that control the cellular responses to various stimuli.
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