Ubiquitin-conjugating enzyme V variant 1 enables cellular responses toward fibroblast growth factor signaling in endothelium.

Ubiquitination has been shown to provide an essential regulatory role in modulating the duration and amplitude of the signaling activity in angiogenesis. While successive enzymatic reactions mediated by three distinct types of enzymes commonly known as E1, E2, and E3 are required for ubiquitination, the role of E3s which govern the final step of ubiquitination has been extensively analyzed in angiogenesis. In contrast, the role of E2s, which determine the context and functional consequences of ubiquitination, remains largely unknown with respect to angiogenesis. To better elucidate the role of E2s in modulating endothelial behaviors during angiogenesis, we first systematically analyze the expression pattern of E2s in endothelial cells (ECs) using previously published scRNA-seq data and identify ubiquitin-conjugating enzyme variant 1 (UBE2V1), an unconventional E2 without innate catalytic activity, as one of the most abundantly expressed E2s in ECs. While ubiquitously expressed in diverse cell types, abrogation of UBE2V1 significantly impairs proliferation and viability of human umbilical vein endothelial cells (HUVECs) without affecting other cell types, suggesting that UBE2V1 is likely to possess nonredundant functions in ECs. Consistent with this idea, UBE2V1 appears to be critical for morphogenesis and migration of ECs during angiogenesis. Interestingly, we find that UBE2V1 is essential for fibroblast growth factor 2 (FGF2)-induced angiogenesis, but appears to have minor effects on vascular endothelial growth factor-A-induced angiogenesis in vitro as well as in vivo. Therefore, it seems that UBE2V1 could enable ECs to distinguish two related yet distinct angiogenic cues. Mechanistically, we show that UBE2V1 promotes ubiquitination of MEK kinase 1, a key mediator of FGF2 signaling, to enhance phosphorylation of extracellular signal-regulated kinase 1/2 in HUVECs. Taken together, our results illustrate the unique role of UBE2V1 as a key modulator for angiogenic behaviors in ECs.