BCL-2 isoform β promotes angiogenesis by TRiC-mediated upregulation of VEGF-A in lymphoma

Bcl-2 (B-cell lymphoma 2), the first identified anti-apoptosis factor, encodes two transcripts, the long isoform α and the short isoform β. The current understanding of the Bcl-2 function mainly focuses on Bcl-2α, while little is known about the function of Bcl-2β, which lacks the transmembrane domain and contains 10 unique amino acids at the C-terminus instead. Here, we analyzed the expressions of BCL-2 two isoforms in diffused large B-cell lymphoma (DLBCL) and found a significant positive correlation between them. Then, with the CRISPR/Cas9-based transcriptional activator (CRISPRa), we generated mouse B-cell lymphomas with Bcl-2 upregulation from the endogenous locus, in which both Bcl-2α and Bcl-2β levels were increased. Bcl-2β itself promoted angiogenesis both in vitro and in vivo through increased vascular endothelial growth factor A (VEGF-A). Inhibiting VEGF receptors with Axitinib reduced angiogenesis induced by Bcl-2β overexpression. Co-immunoprecipitation and mass spectrometry analysis revealed that Bcl-2β interacted with the T-complex protein ring complex (TRiC). Disruption of TRiC significantly impaired the angiogenesis-promoting activity of Bcl-2β, indicated by reduced VEGF-A protein level and HUVEC tube formation. Thus, our study suggests that Bcl-2 isoform β plays a role in promoting tumor angiogenesis through the Bcl-2β-TRiC-VEGF-A axis.