Proteasome-dependent degradation of ERalpha but not ERbeta in cultured mouse aorta smooth muscle cells.

摘要

Here we investigate ERalpha and ERbeta expression and regulation in vascular smooth muscle cells from mouse aorta. Immunocytochemistry showed nuclear staining for both ERalpha and ERbeta. Double stainings revealed co-expression of ERalpha and ERbeta in vascular smooth muscle cells. ERalpha (66 kDa) and ERbeta (54 kDa) expression determined by Western blotting was unchanged within 7 h after inhibition of protein synthesis with cycloheximide in the absence of 17beta-estradiol (E(2)), showing that both proteins are stable without ligand-binding. Treatment with 10 nM E(2) for 7 h in the presence of cycloheximide increased ERalpha, suggesting that E(2) causes a conformational change in the ERalpha protein. The ERbeta was not affected by E(2). Treatment with the proteasome inhibitor epoxomicin (100 nM) for 3 days caused a prominent upregulation of ERalpha both in the absence and in the presence of E(2), while ERbeta was unaffected, suggesting that ERalpha but not ERbeta is degraded by ubiquitin-proteasome system in vascular smooth muscle cells. In summary, we disclose a short-term regulation of ERalpha protein by estrogen and that ERalpha but not ERbeta is degraded via the ubiquitin-proteasome pathway in vascular smooth muscle cells.