CD13 activation assembles phosphoinositide (PI) signaling complexes to regulate the actin cytoskeleton

Activation of transmembrane CD13 enables diverse cellular processes such as cell-cell and cell-matrix adhesion, endocytosis, and recycling of cell surface proteins by assembling and tethering protein complexes at the plasma membrane. Here, we identify a novel CD13-dependent protein assembly that regulates phosphoinositide (PI) signal transduction to impact actin dynamics and induce cell protrusions capable of propagating signals to distant cells. In response to cellular stress, the CD13-expressing human Kaposi's sarcoma-derived cell line (KS1767, KSCs) formed elongated protrusions that extend above the substrate and link non-adjacent cells, which is significantly diminished in CD13^KO KSCs. Activation of CD13 with stimulating mAbs markedly induced protrusion formation with a striking accumulation of CD13 and actin at the base. Further, these membrane-delimited bridges in WT KSCs can transfer Ca²⁺ signals between connected cells via Connexin 43⁺ gap junctions. Mechanistically, CD13-mediated protrusion formation requires activation of CD13, Src, FAK and Cdc42 to tether the IQGAP1 and ARF6 complex at the membrane. This activates phosphatidylinositol-4-phosphate-5-kinase (PI5K) to increase local phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) levels, promoting actin-polymerization and membrane protrusion. Therefore, CD13 is a novel molecular PIP regulator, modulating signal transduction and downstream cellular processes, including actin cytoskeleton dynamics and membrane organization to facilitate intercellular communication.