PT  - JOURNAL ARTICLE
AU  - Cesar Moncada de la Rosa
AU  - Aneta Radziwon-Balicka
AU  - Haitham El-Sikhry
AU  - John Seubert
AU  - Peter P. Ruvolo
AU  - Marek W. Radomski
AU  - Paul Jurasz
TI  - Pharmacologic Protein Kinase C<em>α</em> Inhibition Uncouples Human Platelet-Stimulated Angiogenesis from Collagen-Induced Aggregation
AID  - 10.1124/jpet.112.200881
DP  - 2013 Apr 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 15--24
VI  - 345
IP  - 1
4099  - http://jpet.aspetjournals.org/content/345/1/15.short
4100  - http://jpet.aspetjournals.org/content/345/1/15.full
SO  - J Pharmacol Exp Ther2013 Apr 01; 345
AB  - Platelets promote angiogenesis by releasing angiogenesis-regulating factors from their α-granules upon aggregation. This effect has both physiologic and pathologic significance as it may contribute to carcinogenesis. Platelet α-granule release and aggregation are regulated, in part, via protein kinase C (PKC) α and β signaling. Our study investigated the effects of PKC inhibition on aggregation, angiogenesis-regulator secretion from α-granules, and platelet-stimulated angiogenesis. We hypothesized that selective PKCα inhibition may preferentially suppress angiogenesis-regulator secretion from α-granules but not aggregation, limiting platelet-stimulated angiogenesis. Human platelets were aggregated in the presence of conventional PKC inhibitors myr-FARKGALRQ and Ro 32-0432 (2-{8-[(dimethylamino)methyl]-6,7,8,9-tetrahydropyridol[1,2-α]indol-3-yl}-3-(1-methyl-1H-indol-3-yl)maleimide). Immunofluorescence microscopy of PKC translocation was used to determine the specificity of PKC-inhibitor targeting. Enzyme-linked immunosorbent assay was used to measure vascular endothelial growth factor (VEGF) and thrombospondin-1 (TSP-1) release from platelets. Platelet effects on angiogenesis were tested using a capillary-formation assay. Ro 32-0432, but not the peptide inhibitor myr-FARKGALRQ (myristoylated-pseudosubstrate peptide inhibitor), inhibited aggregation in a concentration-dependent manner, while both Ro 32-0432 and myr-FARKGALRQ preferentially suppressed VEGF over TSP-1 secretion. Suppression of angiogenesis-regulator release occurred at inhibitor concentrations that did not significantly affect aggregation. Immunofluorescence microscopy revealed that PKCα targeting to α-granules is inhibited when angiogenesis-regulator secretion is uncoupled from aggregation. At concentrations that uncoupled α-granule release from aggregation, Ro 32-0432 and myr-FARKGALRQ inhibited platelet-stimulated angiogenesis. Hence, selective PKCα inhibition suppresses angiogenesis-regulator release from platelet α-granules with minimal effects on aggregation. Thus, selective PKCα inhibitors may have pharmacologic significance to regulate platelet-promoted angiogenesis.