Ethanol Exposure Results in a Transient Decrease in Human Platelet cAMP Levels: Evidence for a Protein Kinase C Mediated Process

SummaryP-selectin is translocated from the α-granules to the surface of activated platelets where it participates in thrombosis and inflammation. We investigated the signaling pathways involved in thrombin-induced human platelet P-selectin expression. Assessed by flow cytometry, inhibition of protein kinase C (PKC) with chelerythrine reduced P-selectin expression by 66%, platelet/neutrophil binding, GPIIb/IIIa activation and aggregation (p<0.05). Gö 6976, an inhibitor of the conventional PKCs (α and β), did not alter P-selectin expression. However, rottlerin inhibited by 50% its expression (p<0.05), but only at doses that interfere with the novel (є, η) and atypical (ζ) PKCs. Inhibition of protein tyrosine kinase (PTK) and phosphoinositide 3-kinase (PI3-K) did not significantly affect P-selectin expression. In conclusion, thrombin-induced P-selectin expression is PKC-sensitive, but PTK and PI3-K-insensitive. The novel є and η and atypical ζ, but not the conventional α and β and the novel θ PKCs, may be involved in this process.

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Stimulation of tissue plasminogen activator production by retinoic acid: synergistic effect on protein kinase C-mediated activation

Blood ◽

10.1182/blood.v80.4.981.981 ◽

1992 ◽

Vol 80 (4) ◽

pp. 981-987 ◽

Cited By ~ 1

Author(s):

RD Medh ◽

L Santell ◽

EG Levin

Keyword(s):

Endothelial Cells ◽

Protein Kinase C ◽

Retinoic Acid ◽

Protein Kinase ◽

Hela Cells ◽

Additive Effect ◽

Kinase C ◽

Tissue Plasminogen ◽

Camp Levels ◽

Stimulation Of

Abstract Trans retinoic acid (t-RA) stimulated the production of tissue plasminogen activator (tPA) in HeLa-S3 and human umbilical vein endothelial cells (huvecs) in a dose-dependent manner with maximal release (four to five times control) at 40 nmol/L and 40 mumol/L, respectively. In endothelial cells, the stimulation of tPA production by phorbol 12-myristate 13-acetate (PMA) was potentiated 1.9-fold by 10 mumol/L t-RA, or 1.8 times the additive effect. In HeLa cells, total tPA secretion with 10 nmol/L PMA was increased from 43 ng/mL to 96 ng/mL by 40 nmol/L t-RA, which was two times the additive effect. Higher concentrations of t-RA (400 nmol/L) depressed tPA secretion by itself and also suppressed PMA-induced tPA production by 50%. Histamine and thrombin also synergized with t-RA. t-RA (40 nmol/L) and 10 micrograms/mL histamine or 10 U/mL thrombin combined to induce tPA production 3.4 and 1.3 times the additive effect in HeLa cells. Cyclic adenosine monophosphate (cAMP) levels were not significantly affected by 10 nmol/L to 10 mumol/L t-RA. Nor did 10 nmol/L PMA and 40 nmol/L t- RA together affect cAMP levels, suggesting that t-RA-mediated potentiation of PMA-induced tPA production occurred via a mechanism that was independent of cAMP levels. Downregulation of protein kinase C (PKC) by pretreatment of huvecs with 100 nmol/L PMA completely blocked a secondary response to PMA, but did not have a significant effect on t- RA induction. Pretreatment with 10 mumol/L t-RA, on the other hand, did not significantly affect a secondary stimulus by 100 nmol/L PMA, but completely suppressed a secondary stimulation by 10 mumol/L t-RA alone. These studies suggest that the mechanism mediating t-RA stimulation of tPA production interacts with the PKC pathway, resulting in synergism.

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