Abstract 302: Distinct Regulation of Angiogenic Functions in Endothelial Cells by Class I and II Histone Deacetylases: Role of Specific Isoforms
Posttranslational histone modification contributes as a co-activating or -repressing mechanism to the regulation of gene transcription. Histone acetylation is regulated by histone deacetylases (HDAC) including the Trichostatin A (TSA) -sensitive HDAC classes I and II. Since TSA inhibits angiogenesis, we investigated the role of individual class I and II HDAC isoenzymes for angiogenesis in vitro. siRNA-mediated specific suppression of class I HDACs 2 or 3, class IIa HDACs 7 or 9, or of class IIb HDAC6 was controlled by RT-PCR. Each inhibited endothelial cell (EC) migration in a scratched-wound assay (Fig. A⇓, * p<0.05). In parallel, when we assessed pro-angiogenic capacities by measuring capillary sprout formation from three-dimensional EC spheroids, the cumulative sprout length likewise decreased in cells treated with siRNA against HDACs 3, 6, or 7 (Fig. B⇓). In contrast, surprisingly, siRNA against class IIa HDACs 4 or 5 enhanced both, migration and sprouting. HDAC6 and HDAC9 siRNA slightly reduced EC proliferation by ~30%, whereas siRNA against other isoenzymes did not significantly affect cell cycle progression. None of the siRNA led to cell death induction >7.5%, suggesting that regulation of EC migration and sprouting is not secondary to cell cycle effects. By immunoblot analysis, knock-down of individual HDACs did not induce genome-wide histone hyperacetylation (between 90± 8 and 113± 19% of control; TSA: 178± 21%, p<0.05). In summary, various HDAC isoenzymes differentially regulate EC migration and capillary sprouting. The distinct roles of individual HDACs suggest that HDAC isoforms may regulate gene-specific transcriptional complexes in EC.