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Mechanisms of inhibition by heparin of PDGF stimulated MAP kinase activation in vascular smooth muscle cells.
J Cell Physiol. 1997 Jul; 172(1):69-78.JC

Abstract

Heparin and heparan are potent inhibitors of vascular smooth muscle cell (VSMC) proliferation. To investigate the mechanisms by which heparin suppresses growth factor stimulated mitogenesis, the present experiments investigated the effects of heparin on platelet-derived growth factor (PDGF) stimulated signal transduction pathways. Heparin treatment substantially inhibited PDGF-BB stimulated rat VSMC growth. Western analysis showed a 30 min PDGF-BB treatment of VSMC induced the tyrosine phosphorylation of multiple protein bands; cotreatment with heparin inhibited mitogen-activated protein (MAP) kinase tyrosine phosphorylation but had little effect on PDGF receptor tyrosine phosphorylation. In-gel kinase assays demonstrated that heparin inhibited PDGF-BB stimulated MAP kinase activity at late (25 min) but not early (10 min) time points. These data indicate that heparin does not inhibit the initial signalling events after PDGF-BB binding but instead acts through an alternate mechanism to inhibit MAP kinase. To investigate if heparin directly stimulates tyrosine phosphatase-mediated suppression of MAP kinase, we treated VSMC with orthovanadate, a tyrosine phosphatase inhibitor. Heparin inhibited MAP kinase tyrosine phosphorylation after orthovanadate treatment, indicating that heparin does not suppress MAP kinase by enlistment of a tyrosine phosphatase. Experiments were performed to investigate signalling pathways upstream of MAP kinase. To determine if protein kinase C (PKC) mediates PDGF-BB, serum, and EGF stimulation of MAP kinase, we treated VSMC overnight with phorbol ester (PMA) to downregulate PKC. Abolition of conventional and novel PKC activity significantly suppressed both serum and PDGF-BB induced MAP kinase activation, indicating protein kinase C is an important mediator for these mitogens. In contrast, downregulation of these PKC isoforms had little effect on EGF stimulation of MAP kinase. As heparin inhibits PDGF and serum but not EGF stimulation of MAP kinase, there data precisely correlate heparin inhibition of MAP kinase with activation through PKC-dependent pathways. Immunoprecipitation analysis found that heparin inhibited serum, PMA, and PDGF but not EGF induced raf-1 phosphorylation. These studies demonstrate that heparin did not block PDGF-BB receptor activation, which initiates the mitogenic signalling cascade. Heparin did inhibit specific postreceptor second messenger signals, such as the late phase activation of MAP kinase, which may be mediated by suppression of PKC-dependent pathways.

Authors+Show Affiliations

Department of Pathology, Harvard Medical School, Boston, MA 02115, USA. lapuk@warren.med.harvard.eduNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

9207927

Citation

Pukac, L A., et al. "Mechanisms of Inhibition By Heparin of PDGF Stimulated MAP Kinase Activation in Vascular Smooth Muscle Cells." Journal of Cellular Physiology, vol. 172, no. 1, 1997, pp. 69-78.
Pukac LA, Carter JE, Ottlinger ME, et al. Mechanisms of inhibition by heparin of PDGF stimulated MAP kinase activation in vascular smooth muscle cells. J Cell Physiol. 1997;172(1):69-78.
Pukac, L. A., Carter, J. E., Ottlinger, M. E., & Karnovsky, M. J. (1997). Mechanisms of inhibition by heparin of PDGF stimulated MAP kinase activation in vascular smooth muscle cells. Journal of Cellular Physiology, 172(1), 69-78.
Pukac LA, et al. Mechanisms of Inhibition By Heparin of PDGF Stimulated MAP Kinase Activation in Vascular Smooth Muscle Cells. J Cell Physiol. 1997;172(1):69-78. PubMed PMID: 9207927.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Mechanisms of inhibition by heparin of PDGF stimulated MAP kinase activation in vascular smooth muscle cells. AU - Pukac,L A, AU - Carter,J E, AU - Ottlinger,M E, AU - Karnovsky,M J, PY - 1997/7/1/pubmed PY - 2000/6/20/medline PY - 1997/7/1/entrez SP - 69 EP - 78 JF - Journal of cellular physiology JO - J Cell Physiol VL - 172 IS - 1 N2 - Heparin and heparan are potent inhibitors of vascular smooth muscle cell (VSMC) proliferation. To investigate the mechanisms by which heparin suppresses growth factor stimulated mitogenesis, the present experiments investigated the effects of heparin on platelet-derived growth factor (PDGF) stimulated signal transduction pathways. Heparin treatment substantially inhibited PDGF-BB stimulated rat VSMC growth. Western analysis showed a 30 min PDGF-BB treatment of VSMC induced the tyrosine phosphorylation of multiple protein bands; cotreatment with heparin inhibited mitogen-activated protein (MAP) kinase tyrosine phosphorylation but had little effect on PDGF receptor tyrosine phosphorylation. In-gel kinase assays demonstrated that heparin inhibited PDGF-BB stimulated MAP kinase activity at late (25 min) but not early (10 min) time points. These data indicate that heparin does not inhibit the initial signalling events after PDGF-BB binding but instead acts through an alternate mechanism to inhibit MAP kinase. To investigate if heparin directly stimulates tyrosine phosphatase-mediated suppression of MAP kinase, we treated VSMC with orthovanadate, a tyrosine phosphatase inhibitor. Heparin inhibited MAP kinase tyrosine phosphorylation after orthovanadate treatment, indicating that heparin does not suppress MAP kinase by enlistment of a tyrosine phosphatase. Experiments were performed to investigate signalling pathways upstream of MAP kinase. To determine if protein kinase C (PKC) mediates PDGF-BB, serum, and EGF stimulation of MAP kinase, we treated VSMC overnight with phorbol ester (PMA) to downregulate PKC. Abolition of conventional and novel PKC activity significantly suppressed both serum and PDGF-BB induced MAP kinase activation, indicating protein kinase C is an important mediator for these mitogens. In contrast, downregulation of these PKC isoforms had little effect on EGF stimulation of MAP kinase. As heparin inhibits PDGF and serum but not EGF stimulation of MAP kinase, there data precisely correlate heparin inhibition of MAP kinase with activation through PKC-dependent pathways. Immunoprecipitation analysis found that heparin inhibited serum, PMA, and PDGF but not EGF induced raf-1 phosphorylation. These studies demonstrate that heparin did not block PDGF-BB receptor activation, which initiates the mitogenic signalling cascade. Heparin did inhibit specific postreceptor second messenger signals, such as the late phase activation of MAP kinase, which may be mediated by suppression of PKC-dependent pathways. SN - 0021-9541 UR - https://www.unboundmedicine.com/medline/citation/9207927/Mechanisms_of_inhibition_by_heparin_of_PDGF_stimulated_MAP_kinase_activation_in_vascular_smooth_muscle_cells_ L2 - https://doi.org/10.1002/(SICI)1097-4652(199707)172:1<69::AID-JCP8>3.0.CO;2-B DB - PRIME DP - Unbound Medicine ER -