Novel Function for Fibulin-5 in Controlling Integrin-Induced ROS Production: Implications on Angiogenesis and Cancer
Schluterman, Marie Kay
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Tumor survival depends in part on the ability of tumor cells to transform the surrounding extracellular matrix (ECM) into an environment conducive to tumor progression. Matricellular proteins are secreted into the ECM and impact signaling pathways required for pro-tumorgenic activities such as angiogenesis. Fibulin-5 (Fbln5) is a matricellular protein recently shown to regulate angiogenesis, however its effect on tumor angiogenesis and thus tumor growth is currently unknown. We report that the growth of pancreatic tumors and tumor angiogenesis was suppressed in Fbln5 null (Fbln5-/-) mice compared to wild-type (WT) littermates. Furthermore, we observed an increase in the level of reactive oxygen species (ROS) in tumors grown in Fbln5-/- animals. Increased ROS resulted in elevated DNA damage, increased apoptosis of endothelial cells within the tumor and represented the underlying cause for the reduction in angiogenesis and tumor growth. In vitro, we identified a novel pathway by which Fbln5 controls ROS production through a mechanism dependent on _1 integrins. These results were validated in Fbln5RGE/RGE mice, which harbor a point mutation in the integrin-binding RGD motif of Fbln5 preventing its interaction with integrins. Tumor growth and angiogenesis was reduced in Fbln5RGE/RGE mice, however treatment with an antioxidant rescued angiogenesis and elevated tumor growth to WT levels. These findings introduce a novel function for Fbln5 in the regulation of integrin-induced ROS production and establish a rationale for future studies to examine whether blocking Fbln5 function could be an effective anti-tumor strategy, alone or in combination with other therapies.