Integrin Alpha 3 Beta 1 Regulates Kidney Collecting Duct Development Via Traf6-Dependent K63-Linked Polyubiquitination Of Akt

The collecting system of the kidney develops from the ureteric bud (UB), which undergoes branching morphogenesis, a process regulated by multiple factors, including integrin-extracellular matrix interactions. The laminin (LM)-binding integrin alpha 3 beta 1 is crucial for this developmental program; however, the LM types and LM/integrin alpha 3 beta 1-dependent signaling pathways are poorly defined. We show that alpha 3 chain-containing LMs promote normal UB branching morphogenesis and that LM-332 is a better substrate than LM-511 for stimulating integrin alpha 3 beta 1-dependent collecting duct cell functions. We demonstrate that integrin alpha 3 beta 1-mediated cell adhesion to LM-332 modulates Akt activation in the developing collecting system and that Akt activation is PI3K independent but requires decreased PTEN activity and K63-linked polyubiquitination. We identified the ubiquitin-modifying enzyme TRAF6 as an interactor with the integrin beta 1 subunit and regulator of integrin alpha 3 beta 1-dependent Akt activation. Finally, we established that the developmental defects of TRAF6- and integrin alpha 3-null mouse kidneys are similar. Thus K63-linked polyubiquitination plays a previously unrecognized role in integrin alpha 3 beta 1-dependent cell signaling required for UB development and may represent a novel mechanism whereby integrins regulate signaling pathways.