Phosphatidylinositol 3-kinase and focal adhesion kinase are early signals in the growth factor-like responses to thrombospondin-1 seen in human vascular smooth muscle.
Thrombospondin-1 (TSP-1) is a matricellular protein that is expressed in negligible amounts in normal blood vessels but is markedly upregulated in vascular injury. Although TSP-1 can act as a pleiotropic regulator for human vascular smooth muscle cells (HVSMCs), the intracellular signaling pathways stimulated by this protein remain obscure. In cultured HVSMCs derived from saphenous vein, TSP-1 induces tyrosine phosphorylation of a number of cellular proteins, with a complex temporal pattern of activation. Immunoprecipitation techniques have identified the early tyrosine-phosphorylated signals as being the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-K) and focal adhesion kinase (FAK). Tyrosine phosphorylation of the p85 subunit of PI 3-K showed a biphasic response to TSP-1 stimulation, which corresponded to a biphasic activation of the lipid kinase. Treatment with both wortmannin and LY294002 inhibited PI 3-K activity of HVSMCs but did not affect tyrosine phosphorylation of the p85 regulatory subunit. TSP-1-stimulated FAK phosphorylation, however, was substantially reduced by these inhibitors, as was the TSP-1-induced chemotaxis of these cells. These results suggest that activation of PI 3-K is an early signal induced by TSP-1 and is critical for chemotaxis. Activation of this kinase precedes and may occur upstream from FAK phosphorylation, although the nature of the interaction between these 2 enzymes remains obscure.
Lymn
J S
JS
Clinical Pharmacology, National Heart and Lung Institute, Imperial College of Science, Technology & Medicine, St. Mary's Hospital, London.j.lmn@ic.ac.uk
Rao
S J
SJ
Clunn
G F
GF
Gallagher
K L
KL
O'Neil
C
C
Thompson
N T
NT
Hughes
A D
AD
D000730:Androstadienes / Q000494:pharmacology; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002478:Cells, Cultured; D002633:Chemotaxis / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006133:Growth Substances / Q000494:pharmacology*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D019700:Thrombospondin 1 / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism; D000077191:Wortmannin
D000730:Androstadienes; D015815:Cell Adhesion Molecules; D002867:Chromones; D004791:Enzyme Inhibitors; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006133:Growth Substances; D007527:Isoenzymes; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011505:Protein-Tyrosine Kinases; D019700:Thrombospondin 1; D014443:Tyrosine; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C496050:PTK2 protein, human