Abstract 745: DEC1, a Member of the Fifth Clock-Gene Family, is Induced by Angiotensin II, Growth Factors, and Hypoxia in Vascular Cells.
Background: Several parameters of cardiovascular function, including blood pressure, heart rate and coagulation system, vary with a diurnal pattern, which may contribute to the preferential occurrence of some cardiovascular events at particular points in the circadian rhythm. Circadian rhythms are regulated by the interaction between central and peripheral biological clock. We have discovered DEC1, which is a member of fifth clock-gene family and a basic helix-loop-helix transcriptional factor. The goal of the present study was to characterize the input-signals that induce DEC1 in vascular cells.
Methods and Results: The expression of DEC1 was assayed by real-time PCR and Western blot analysis. DEC1 expression varied with a clear circadian oscillation pattern in rat aorta. Stimulation of cultured rat vascular smooth muscle cells (VSMC) with angiotensin II and PDGF resulted in an increase in DEC1 mRNA (3.5-and 9.2-fold, respectively) and protein expression (7.6- and 5.8-fold, respectively) with a peak at 1–2 hours. Similarly, stimulation of human vein umbilical endothelial cells (HUVEC) with VEGF resulted in a marked increase in DEC1 mRNA and protein expression (6.8- and 3.7-fold, respectively). The induction of DEC1 expression by these stimuli was potently blocked by pretreatment with SU6656, which is a specific inhibitor of the Src kinase family, or small interfering RNA (siRNA) against Src. Actinomycin D completely blocked the angiotensin II- and PDGF-induced increase in DEC1 mRNA levels, suggesting that the expression of DEC1 in response to these stimuli is regulated at the transcriptional level. Finally, hypoxia also resulted in increased DEC1 expression in both VSMC and HUVEC, and siRNA-mediated knockdown of hypoxia-inducible factor-1alpha (HIF-1alpha) expression inhibited this effect.
Conclusions: In summary, DEC1 is induced by angiotensin II and growth factors in vascular smooth muscle cells and endothelial cells by a Src-dependent mechanism. DEC1 is also induced by hypoxia via a HIF-1 dependent mechanism. These data suggest that DEC1 may play other roles in the cardiovascular system, aside from its function in regulating circadian rhythms.