VEGF₁₆₅b, a splice variant of VEGF-A, promotes lung tumor progression and escape from anti-angiogenic therapies through a β1 integrin/VEGFR autocrine loop

Abstract

Vascular endothelial growth factor-A (VEGF-A) is highly subjected to alternative pre-mRNA splicing that generates several splice variants. The VEGF_xxx and VEGF_xxxb families encode splice variants of VEGF-A that differ only at the level of six amino acids in their C-terminal part. The expression level of VEGF_xxx splice variants and their function as pro-angiogenic factors during tumor neo-angiogenesis have been well-described. The role of VEGF_xxxb isoforms is less well known, but they have been shown to inhibit VEGF_xxx-mediated angiogenesis, while being partial or weak activators of VEGFR receptors in endothelial cells. On the opposite, their role on tumor cells expressing VEGFRs at their surface remains largely unknown. In this study, we find elevated levels of VEGF₁₆₅b, the main VEGF_xxxb isoform, in 36% of non-small cell lung carcinoma (NSCLC), mainly lung adenocarcinoma (46%), and show that a high VEGF₁₆₅b/VEGF₁₆₅ ratio correlates with the presence of lymph node metastases. At the molecular level, we demonstrate that VEGF₁₆₅b stimulates proliferation and invasiveness of two lung tumor cell lines through a VEGFR/β1 integrin loop. We further provide evidence that the isoform-specific knockdown of VEGF₁₆₅b reduces tumor growth, demonstrating a tumor-promoting autocrine role for VEGF₁₆₅b in lung cancer cells. Importantly, we show that bevacizumab, an anti-angiogenic compound used for the treatment of lung adenocarcinoma patients, increases the expression of VEGF₁₆₅b and activates the invasive VEGFR/β1 integrin loop. Overall, these data highlight an unexpected role of the VEGF₁₆₅b splice variant in the progression of lung tumors and their response to anti-angiogenic therapies.