Okamoto T, Wu Y, Matsuhisa K, Saito A, Sakaue F, Imaizumi K, Kaneko M

We previously reported that RNF183, a member of the RING finger (RNF) protein family, is specifically expressed in the renal collecting duct and that RNF183 mRNA is induced by the activity of nuclear factor of activated T cells 5 (NFAT5), which regulates the transcription of essential proteins for adaptation to ...

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hypertonic conditions. The renal medulla is the only tissue that is continuously hypertonic; therefore, RNF183 possibly plays an important role in adaptation to continuous hypertonic conditions. However, the mechanism of how cells adapt to long-term hypertonicity via RNF183 remains unclear. In this study, the Na, K-ATPase ?1 subunit was identified as a candidate substrate of RNF183 by the BirA proximity-biotinylation technique. The Na, K-ATPase ?1 subunit acts as an ion transporter along with the Na, K-ATPase ?1 subunit at the plasma membrane. We confirmed that RNF183 interacted with both ?1 and ?1 subunits; however, we found that RNF183 ubiquitinated only the ?1 subunit, not the ?1 subunit. Furthermore, RNF183 translocated both ?1 and ?1 subunits from the plasma membrane to lysosomes. In addition, the expression levels of ?1 and ?1 subunits in HEK293?cells stably expressing RNF183 were significantly decreased compared with mock control cells, and were restored by siRNA-mediated knockdown of RNF183. Moreover, in RNF183-expressing cells, chloroquine treatment increased the protein levels of the ?1 and ?1 subunits. Therefore, our results suggest that Na, K-ATPase ?1 and ?1 subunits are degraded in lysosomes by RNF183-mediated ubiquitination of ?1 subunit.

Date: Dec. 22, 2019

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