CD13 Activation Assembles Signaling Complexes that Promote the Formation of Tunneling Nanotubes in Endothelial Cells

Abstract

Transmembrane CD13 assembles protein complexes at the plasma membrane to enable diverse cellular processes such as cell-cell adhesion, focal adhesion turnover, endocytosis and recycling of cell surface proteins. In this study, we demonstrate a novel CD13-dependent assembly platform that regulates phosphoinositide (PI) signal transduction during the formation of Tunneling Nanotubes (TNTs). TNTs are actin-based, membrane-delimited bridges that facilitate intercellular communication by connecting distant cells to physically transfer subcellular cargoes. TNTs form between various cell types under stress conditions, but few molecular TNT-inducers exist. Human Kaposis sarcoma-derived endothelial cells (KSECs) readily form stress-induced TNTs capable of transferring Ca2+ and membrane molecules between cells, with clear accumulation of CD13 and actin at the base of the protrusions. Alternatively, CD13-null KSECs form fewer TNTs and Ca2+ transfer is markedly reduced. Mechanistically, CD13-mediated TNT formation requires activation of CD13, Src, FAK and Cdc42 to allow tethering of the IQGAP1 and ARF6 complex at the membrane to activate the phosphatidylinositol-4-phosphate-5-kinase PI5K. This increases local phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) levels to promote the actin-polymerization and membrane protrusion necessary for TNT formation. Therefore, CD13 is a novel molecular PIP regulator and TNT trigger that will facilitate the dissection of downstream pathways and mechanisms regulating TNT formation.