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Matthew L Jones

Publications and source records attributed to Matthew L Jones.

8 recordsLinked to original sources
PubMed2006

Distinct roles for protein kinase C isoforms in regulating platelet purinergic receptor function.

ADP is a critical regulator of platelet activation, mediating its actions through two G protein-coupled receptors (GPCRs), P2Y1 and P2Y12. We have shown previously that the receptors are functionally desensitized, in a homologous manner, by distinct kinase-dependent mechanisms in which P2Y1 is regulated by protein kinase C (PKC) and P2Y12 by G protein-coupled receptor kinases. In this study, we addressed whether different PKC isoforms play different roles in regulating the trafficking and activity of these two GPCRs. Expression of PKCalpha and PKCdelta dominant-negative mutants in 1321N1 cells revealed that both isoforms regulated P2Y1 receptor signaling and trafficking, although only PKCdelta was capable of regulating P2Y12, in experiments in which PKC was directly activated by the phorbol ester phorbol 12-myristate 13-acetate (PMA). These results were paralleled in human platelets, in which PMA reduced subsequent ADP-induced P2Y1 and P2Y12 receptor signaling. PKC isoform-selective inhibitors revealed that novel, but not conventional, isoforms of PKC regulate P2Y12 function, whereas both novel and classic isoforms regulate P2Y1 activity. It is also noteworthy that we studied receptor internalization in platelets by a radioligand binding approach showing that both receptors internalize rapidly in these cells. ADP-induced P2Y1 receptor internalization is attenuated by PKC inhibitors, whereas that of the P2Y12 receptor is unaffected. Both P2Y1 and P2Y12 receptors can also undergo PMA-stimulated internalization, and here again, novel but not classic PKCs regulate P2Y12, whereas both novel and classic isoforms regulate P2Y1 internalization. This study therefore is the first to reveal distinct roles for PKC isoforms in the regulation of platelet P2Y receptor function and trafficking.

Animals↗
PubMed2006

Plasmodium falciparum erythrocyte invasion: a conserved myosin associated complex.

Host cell invasion by apicomplexan parasites is powered by an actin/myosin motor complex that has been most thoroughly described in Toxoplasma gondii tachyzoites. In T. gondii, two inner membrane complex (IMC) proteins, the peripheral protein TgGAP45 and the transmembrane protein TgGAP50, form a complex with the myosin, TgMyoA, and its light chain, TgMLC1. This complex, referred to as the glideosome, anchors the invasion motor to the IMC. We have identified and characterized orthologues of TgMLC1, TgGAP45 and TgGAP50 in blood-stages of the major human pathogen Plasmodium falciparum, supporting the idea that the same basic complex drives host cell invasion across the apicomplexan phylum. The P. falciparum glideosome proteins are transcribed, expressed and localized in a manner consistent with a role in erythrocyte invasion. Furthermore, PfMyoA interacts with PfMTIP through broadly conserved mechanisms described in other eukaryotes, and forms a complex with PfGAP45 and PfGAP50 in late schizonts and merozoites. P. falciparum is known to use multiple alternative invasion pathways to enter erythrocytes, hampering vaccine development efforts targeting erythrocyte invasion. Our data suggests that the same invasion motor underpins all alternative invasion pathways, making it an attractive target for the development of novel intervention strategies.

Amino Acid Sequence↗
PubMed2005

A SHPing tale: perspectives on the regulation of SHP-1 and SHP-2 tyrosine phosphatases by the C-terminal tail.

Protein tyrosine phosphorylation is a ubiquitous signalling mechanism and is regulated by a balance between the action of kinases and phosphatases. The SH2 domain-containing phosphatases SHP-1 and SHP-2 are the best studied of the classical non-receptor tyrosine phosphatases, but it is intriguing that despite their close sequence and structural homology these two phosphatases play quite different cellular roles. In particular, whereas SHP-1 plays a largely negative signalling role suppressing cellular activation, SHP-2 plays a largely positive signalling role. Major sequence differences between the two molecules are apparent in the approximately 100 amino acid residues at the extreme C-terminus of the proteins, beyond the phosphatase catalytic domain. Here we review how the differences in the tails of these proteins may regulate their activities and explain some of their functional differences.

Amino Acid Sequence↗
PubMed2004

Regulation of SHP-1 tyrosine phosphatase in human platelets by serine phosphorylation at its C terminus.

SHP-1 is a Src homology 2 (SH2) domain-containing tyrosine phosphatase that plays an essential role in negative regulation of immune cell activity. We describe here a new model for regulation of SHP-1 involving phosphorylation of its C-terminal Ser591 by associated protein kinase Calpha. In human platelets, SHP-1 was found to constitutively associate with its substrate Vav1 and, through its SH2 domains, with protein kinase Calpha. Upon activation of either PAR1 or PAR4 thrombin receptors, the association between the three proteins was retained, and Vav1 became phosphorylated on tyrosine and SHP-1 became phosphorylated on Ser591. Phosphorylation of SHP-1 was mediated by protein kinase C and negatively regulated the activity of SHP-1 as demonstrated by a decrease in the in vitro ability of SHP-1 to dephosphorylate Vav1 on tyrosine. Protein kinase Calpha therefore critically and negatively regulates SHP-1 function, forming part of a mechanism to retain SHP-1 in a basal active state through interaction with its SH2 domains, and phosphorylating its C-terminal Ser591 upon cellular activation leading to inhibition of SHP-1 activity and an increase in the tyrosine phosphorylation status of its substrates.

Amino Acid Sequence↗
PubMed2004

Reciprocal cross-talk between P2Y1 and P2Y12 receptors at the level of calcium signaling in human platelets.

Adenosine diphosphate (ADP), an important platelet agonist, acts through 2 G-protein-coupled receptors (GPCRs), P2Y(1) and P2Y(12), which signal through Gq and Gi, respectively. There is increasing evidence for cross-talk between signaling pathways downstream of GPCRs and here we demonstrate cross-talk between these 2 ADP receptors in human platelets. We show that P2Y(12) contributes to platelet signaling by potentiating the P2Y(1)-induced calcium response. This potentiation is mediated by 2 mechanisms: inhibition of adenylate cyclase and activation of phosphatidylinositol 3 (PI 3)-kinase. Furthermore, the Src family kinase inhibitor PP1 selectively potentiates the contribution to the calcium response by P2Y(12), although inhibition of adenylate cyclase by P2Y(12) is unaffected. Using PP1 in combination with the inhibitor of PI 3-kinase LY294002, we show that Src negatively regulates the PI 3-kinase-mediated component of the P2Y(12) calcium response. Finally, we were able to show that Src kinase is activated through P2Y(1) but not P2Y(12). Taken together, we present evidence for a complex signaling interplay between P2Y(1) and P2Y(12), where P2Y(12) is able to positively regulate P2Y(1) action and P2Y(1) negatively regulates this action of P2Y(12). It is likely that this interplay between receptors plays an important role in maintaining the delicate balance between platelet activation and inhibition during normal hemostasis.

Adenosine Diphosphate↗
PubMed2004

PKC-interacting proteins: from function to pharmacology.

Protein kinase C (PKC) is a ubiquitously expressed family of kinases that have key roles in regulating multiple cellular activities. The activity of this family is controlled tightly by several molecular mechanisms, including interaction with binding-partner proteins. These PKC-interacting proteins (C-KIPs) confer specificity for individual PKC isoforms by regulating the activity and cellular localization of PKC isoforms and, subsequently, the ability of these isoforms to specifically regulate cellular functional events. Although many C-KIPs have been identified by genome and proteome-mining approaches, it is important to address the specificity and function of the interactions in greater detail because they might form novel drug targets. In this article, we review recent work on C-KIPs and the implications for pharmacological and therapeutic development.

Animals↗
PubMed2003

Interleukin 12-augmented T cell proliferation of peripheral blood mononuclear cells from HIV-seropositive individuals is associated with interleukin 12 receptor beta 2 upregulation.

Interleukin 12 (IL-12) production is believed to be impaired in individuals with HIV infection and this impairment manifests early in disease, when the CD4(+) cell counts are within normal values. The reduced antigen-specific and mitogen-stimulated T cell-proliferative responses that occur in HIV infection can be corrected by the addition of recombinant human interleukin 12 (rhIL-12). As the IL-12 receptor (IL-12R) is central to the IL-12 signaling pathway, we examined whether the augmentation of antigen-specific proliferation of HIV(+) peripheral blood mononuclear cells (PBMCs) related to altered IL-12R expression. rhIL-12 augmented antigen-specific proliferation of HIV(+) PBMCs but not of HIV(-) PBMCs. Examination of resting PBMCs from HIV(+) and HIV(-) donors showed that neither of these populations expressed IL-12R beta 1 or IL-12R beta 2 chains on their cell surface as detected by flow cytometry. However, examination of mRNA showed that both IL-12R beta 1 and IL-12R beta 2 mRNAs were markedly reduced in HIV(+) PBMCs when compared with HIV(-) PBMCs. After mitogen activation there was an increase in IL-12R beta 1 expression on the cell surface of HIV(+) and HIV(-) PBMCs and this level was not altered by coculture with rhIL-12 or interferon gamma (IFN-gamma). However, coculture of phytohemagglutinin (PHA)-activated HIV(+) or HIV(-) PBMCs with rhIL-12 (but not IFN-gamma) increased IL-12R beta 2 expression on the cell surface of both populations. Examination at the message level showed a correction of IL-12R beta 1 to normal levels with activation that was further enhanced by rhIL-12 coculture for both the HIV(+) and HIV(-) PBMCs. However, although the level of IL-12R beta 2 for the HIV(+) PBMCs was normalized by PHA, rhIL-12 caused a further augmentation. This information provides a strong link between IL-12R upregulation, and the significant improvement in antigen-specific HIV-proliferative responses seen with the addition of rhIL-12. It also reveals that the dysfunction in IL-12R expression seen in cells from HIV(+) patients occurs at the transcriptional level. In addition, we provide further evidence that IL-12R beta 1 and IL-12R beta 2 regulation in human PBMCs is independent of IFN-gamma.

HIV Infections↗