Regulation of enhanced vacuolar H+-ATPase expression in macrophages.
The proton-translocating vacuolar ATPase (V-ATPase) acidifies the endocytic network of eukaryotic cells. Although all eukaryotic cell types require low to moderate levels of V-ATPase, some proton-secreting cells express amplified levels for use in specialized membrane domains. To characterize genetic elements required for this heightened expression, we studied transcription and stability of mRNA encoding the V-ATPase c subunit in a low expressing fibroblast cell line (NIH 3T3) and a high expressing macrophage cell line (RAW 264.7). Isolation of the promoter and mapping of the transcriptional start site indicated that the c subunit promoter is TATA-less and initiates transcription at a single site. Promoter activity was regulated through the same transcription factor binding sites in both cell types, which showed no discernible difference in rates of c subunit transcription. In contrast, c subunit transcripts showed markedly greater stability in RAW cells than in 3T3 cells, as did other constitutively expressed V-ATPase subunit transcripts. Only the B and 'a' subunits, which are expressed in multiple isoforms, were not regulated solely by mRNA stability. These results suggest that overall expression levels of the V-ATPase are set primarily by regulation of mRNA stability and that transcriptional mechanisms determine subunit composition in varying cell types.[1]References
- Regulation of enhanced vacuolar H+-ATPase expression in macrophages. Wang, S.P., Krits, I., Bai, S., Lee, B.S. J. Biol. Chem. (2002) [Pubmed]
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