Dysregulation of protein homeostasis by mutant UBA1 in VEXAS syndrome [RNA-seq]

VEXAS is a hematopoietic disorder characterized by hyperinflammation,high mortality, and mutations at methionine 41 (M41) in the E1 ubiquitin enzyme, UBA1. Here, we developed ahuman model of VEXAS by engineering the male THP1 cell line to express the UBA1-M41V mutation. We found that UBA1-M41V cells exhibit aberrant UBA1 isoform expression, increased vacuolization, and upregulation of the unfolded protein response, recapitulating features of VEXAS.Proteomic analyses revealed dysregulated ubiquitination and proteotoxic stress in UBA1-M41V cells, with alterations in inflammatory and stress-response pathways. UBA1-M41V cells were sensitive to genetic or pharmacological inhibition of E1 enzymes. Treatment with theE1 inhibitor TAK-243 preferentially suppressed colony formation of UBA1-M41V cells. Moreover,UBA1-M41V cells exhibited greater sensitivity to TAK-243 in competition assays and showed increased apoptosis. Interestingly, TAK-243 preferentially inhibited UBA6 activity over UBA1 ,suggesting that UBA6 may compensate for UBA1 dysfunction. Targeting UBA6 using shRNA orthe UBA6-specific inhibitor phytic acid further revealed an acquired dependency on UBA6 inUBA1-M41V cells. Phytic acid impaired UBA1-M41V cells while sparing WT cells. Together, these findings establish a novel human model of VEXAS, identify key roles for UBA1 and UBA6, and demonstrate that UBA6 inhibition represents a therapeutic strategy for selectively targeting UBA1 mutant clones.