Journal
CELLS
Volume 11, Issue 16, Pages -Publisher
MDPI
DOI: 10.3390/cells11162546
Keywords
MAGED2; hypoxia; G-alpha-S; MDM2; Bartter
Categories
Funding
- German Research Foundation (DFG) [Ko1855/4-1]
- Stiftung P.E. Kempkes [03/2018]
- University Medical Center Giessen and Marburg UKGM [15/2021]
- Open Access Publication Fund of Philipps-Universitat Marburg
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)
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Mutations in MAGED2 cause transient Bartter syndrome characterized by severe renal salt wasting in fetuses and infants. MAGED2 is shown to be essential for the cAMP/PKA pathway under hypoxia by regulating G alpha s endocytosis through blocking MDM2-dependent ubiquitination of G alpha s.
Mutations in MAGED2 cause transient Bartter syndrome characterized by severe renal salt wasting in fetuses and infants, which leads to massive polyhydramnios causing preterm labor, extreme prematurity and perinatal death. Notably, this condition resolves spontaneously in parallel with developmental increase in renal oxygenation. MAGED2 interacts with G-alpha-S (G alpha s). Given the role of G alpha s in activating adenylyl cyclase at the plasma membrane and consequently generating cAMP to promote renal salt reabsorption via protein kinase A (PKA), we hypothesized that MAGED2 is required for this signaling pathway under hypoxic conditions such as in fetuses. Consistent with that, under both physical and chemical hypoxia, knockdown of MAGED2 in renal (HEK293) and cancer (HeLa) cell culture models caused internalization of G alpha s, which was fully reversible upon reoxygenation. In contrast to G alpha s, cell surface expression of the beta 2-adrenergic receptor, which is coupled to G alpha s, was not affected by MAGED2 depletion, demonstrating specific regulation of G alpha s by MAGED2. Importantly, the internalization of G alpha s due to MAGED2 deficiency significantly reduced cAMP generation and PKA activity. Interestingly, the internalization of G alpha s was blocked by preventing its endocytosis with dynasore. Given the role of E3 ubiquitin ligases, which can be regulated by MAGE-proteins, in regulating endocytosis, we assessed the potential role of MDM2-dependent ubiquitination in MAGED2 deficiency-induced internalization of G alpha s under hypoxia. Remarkably, MDM2 depletion or its chemical inhibition fully abolished G alpha s-endocytosis following MAGED2 knockdown. Moreover, endocytosis of G alpha s was also blocked by mutation of ubiquitin acceptor sites in G alpha s. Thus, we reveal that MAGED2 is essential for the cAMP/PKA pathway under hypoxia to specifically regulate G alpha s endocytosis by blocking MDM2-dependent ubiquitination of G alpha s. This may explain, at least in part, the transient nature of Bartter syndrome caused by MAGED2 mutations and opens new avenues for therapy in these patients.
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