Inhibition of beta1 integrin and IL-3Rbeta common subunit interaction hinders tumour angiogenesis

Integrin/cytokine receptor interaction provides permissive signals leading to neoangiogenesis, and integrins are crucial for differentiation of endothelial progenitor cells (EPCs). It is known that the inflammatory interleukin-3 (IL-3), released in the tumoral microenvironment, contributes to both angiogenesis and vasculogenic processes. Herein, we generated IL-3 receptor beta common (IL-3Rbetac) extracellular domain-derived fusion proteins (Fc) to elucidate the molecular mechanisms regulating these processes. Three different Fc were generated, containing the entire extracellular domain of IL-3Rbetac (Fc1.4), a fragment corresponding to domains 1-3 (Fc1.3) and a fragment corresponding to domain 4 (Fc4), respectively. The ability of the fusion proteins to interfere with IL-3Rbetac/beta1 integrin interaction was assessed on endothelial cells (ECs), EPCs and murine-derived ECs. Pull-down experiments showed that Fc1.4 and Fc4 fusion proteins specifically interacted with beta1 integrin. Fc4 and Fc1.4 fragments prevented IL-3-mediated EPC expansion, arterial morphogenesis and tumour-derived EC migration, without affecting cell adhesion. Fc4 in vivo inhibited the IL-3-mediated vasculogenic process, as well as inflammatory and tumour vascular growth. In conclusion, these data identify the beta1 integrin-interacting domain in the juxta-membrane IL-3Rbetac extracellular domain, and provide the rational for targeting this interaction to impair vascular growth