A novel cellular survival factor – the B2 subunit of vacuolar H+-ATPase inhibits apoptosis

Abstract

The ubiquitous vacuolar H þ -ATPase, a multisubunit proton pump, is essential for intraorganellar acidification. Disruption of its function leads to disturbances of organelle function and cell death. Here, we report that overexpression of the B2 subunit of the H þ -ATPase inhibits apoptosis. This antiapoptotic effect is not mediated by an increase in H þ -ATPase activity but through activation of the Ras-mitogen-activated protein kinase (MAPK)-signaling pathway that results in the serine phosphorylation of Bad at residues 112 and 155. Increased Bad phosphorylation reduces its translocation to mitochondria, limits the release of mitochondrial cytochrome c and apoptosis-inducing factor and increases the resistance of the B2 overexpressing cells to apoptosis. Screening experiments of kinase inhibitors, including inhibitors of cAMP-activated protein kinase, protein kinase C, protein kinase B, (MAPK/extracellular signal-regulated (ERK) kinase) MEK and Ste-MEK1 13 , a cell permeable ERK activation inhibitor peptide, revealed that the B2 subunit of H þ -ATPase acts upstream of MEK activation in the MEK/ERK pathway to ameliorate apoptosis.

V-ATPase promotes transforming growth factor-β-induced epithelial-mesenchymal transition of rat proximal tubular epithelial cells

“…It is reported that free unassembled subunits of the V-ATPase exist in a dynamic balance between the assembled and unassembled forms in cells (31). The free unassembled subunits of this enzyme play other functional roles, such as in cell differentiation, proliferation, and cell death, in addition to forming the enzyme complex for proton transport (18,19,25). Our previous report showed that the B2 subunit has an additional antiapoptotic effect, which is not mediated by an increase in V-ATPase activity but through activation of the Ras-MAPK signaling pathway that results in the serine phosphorylation of Bad residues 112 and 155 (19).…”

“…The free unassembled subunits of this enzyme play other functional roles, such as in cell differentiation, proliferation, and cell death, in addition to forming the enzyme complex for proton transport (18,19,25). Our previous report showed that the B2 subunit has an additional antiapoptotic effect, which is not mediated by an increase in V-ATPase activity but through activation of the Ras-MAPK signaling pathway that results in the serine phosphorylation of Bad residues 112 and 155 (19). Lee et al (18) revealed that the B2 subunit could be upregulated independently of the other subunits by increased transcription of a novel factor through an AP-2 site during monocytic differentiation.…”

“…EMT is also associated with actin reorganization, tubular basement membrane disruption, cell migration, and production of profibrotic molecules (11,15,20,36). Transforming growth factor-␤1 (TGF-␤1) is believed to play an important role in EMT and is likely the most potent EMT inducer (19,36). However, recent studies have cast doubt on the extent to which EMT contributes to kidney fibrosis in vivo (14).…”

“…V-ATPase might be a therapeutic target for many cancers (8,28). Our previous study found that the B2 subunit of V-ATPase is a cell survival factor that can inhibit apoptosis (19). Apoptosis and EMT have been implicated in a variety of biological processes, such as embryonic development, fibrosis, and tumor progression.…”

Modulation of vH+-ATPase is part of the functional adaptation of sheep rumen epithelium to high-energy diet

“…Normal vH ϩ -ATPase activity has been shown to be essential for cell proliferation, growth, viability, and survival (20,23,29,30,47,53), and increasing evidence suggests that the pump is a main component of signal transduction pathways regulating these processes. Dechant et al (7) identified the vH ϩ -ATPase as a sensor of pH i changes and novel activator of PKA in response to glucose uptake and phosphorylation.…”