The mechanisms and possible significance of upregulation of stomatin expression by hypoxia and/or glucocorticoids

Stomatin is an important lipid-raft-associated protein that is thought to bind to various membrane proteins, thereby regulating their biological activities, but little is known about the regulation of stomatin under physiological and pathophysiological conditions. In this study, using real-time PCR and western blotting assays, we found that hypoxia and the synthetic glucocorticoid dexamethasone (Dex), either alone or together, induced the expression of stomatin in the lungs of rats, in lung adenocarcinoma epithelial (A549) cells and in primary alveolar epithelial cells. Using confocal microscopy, we found that enhanced-GFP-tagged stomatin proteins co-localized with membrane-associated actin filaments. In addition, inhibiting stomatin expression by RNA interference markedly decreased the peripheral actin ring in hypoxic or Dex-treated A549 cells. This finding indicates that the upregulation of stomatin expression by hypoxia or Dex could stabilize membrane-associated actin in alveolar epithelial cells, which may enhance the function of the alveolar epithelial barrier under hypoxic conditions. Furthermore, we found that in A549 cells, both hypoxia and Dex could enhance the stability of stomatin mRNA (extending its half-life from 32 h to 39 h and 46.3h, respectively). Dex can also induce stomatin gene promoter activity. Deletion and mutational studies of the stomatin promoter demonstrated that the region -162 to +244 with respect to the transcription start site is essential for both basal and Dex-induced promoter activity. A potential glucocorticoid response element located 3 bases upstream of the transcription start site of the human stomatin gene is the main contributer to the upregulation of stomatin expression by Dex.