Hypoxia‐Induced Ubiquitination Regulates 14‐3‐3η‐Gremlin‐1 Interactions in a Hypoxia Model of Pulmonary Hypertension.

Pulmonary Hypertension ( PH ) is characterized by increased pulmonary artery pressure andresistance, right ventricle ( RV ) hypertrophy, RV failure and death. Increased vascular cell proliferation and vascularremodeling contribute to PH progression, though the mechanisms are incompletelydefined. The ubiquitin proteasome system ( UPS )regulates cellular homeostasis through post‐translational modification oftarget proteins with ubiquitin moieties that direct protein degradation, protein‐proteininteractions, activity, or localization. Massspectrometry analysis of lungs from mice exposed to normoxia or hypoxia,revealed hypoxia‐induced changes in protein ubiquitination. Hypoxia caused a 2.4‐fold increase inubiquitination of 14‐3‐3eta ( 14‐3‐3η ) at lysine ( K )50 (p<0.05) with no change in 14‐3‐3η protein levels. Dysregulation ofthe 14‐3‐3 family of binding proteins is known to promote tumor cellproliferation and migration pathways. We hypothesized that 14‐3‐3η K50 ubiquitinationmay change protein activity since K49/50 is known to play an important role in14‐3‐3 function. K50 is also near the binding site for Gremlin‐1, a proteinthat promotes proliferation by inhibiting bonemorphogenetic protein ( BMP )signaling. Immunoprecipitation of 14‐3‐3η from hypoxia‐exposed mouse lungdemonstrated that hypoxia reduced binding of 14‐3‐3η to Gremlin‐1. IncreasedGremlin‐1 to BMP2 binding was also observed in hypoxia‐exposed mouse lungs,suggesting that Gremlin‐1/BMP2 binding may contribute to disrupted BMPsignaling previously observed in hypoxia. Expression of a lysine to argininemutation at 14‐3‐3η K50 ( K50R ) whichprevents ubiquitination of K50 without altering the local polarity or shape inhuman pulmonary artery endothelial cells, promotes 14‐3‐3η/Gremlin‐1interaction in hypoxia. These findings demonstrate that K50 ubiquitination regulates14‐3‐3η function and its interaction with Gremlin‐1. We speculate thathypoxia‐induced increases in 14‐3‐3η K50 ubiquitination reduce Gremlin‐1 bindingwhich in turn binds BMP ligands to reduce BMP signaling and thereby promote vascularcell proliferation and PH pathogenesis. Support or Funding Information Merit Review funding from the Department of Veterans Affairs, Office ofResearch and Development 1I01BX001910 (CMH), NIH Grant RO1HL102167 (CMH and RLS), NIH T32 HL076118 and 16POST30930007 (BEW). MS work was performed by the Emory Integrated Proteomics Core This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .