Fig 2: Hypothetic molecular model for the role of F-actin network reorganization as a main biomechanical driver for granulocyte trogocytosis of cancer cellsThe generation and maintenance of an immune synapse starts with CD18/CD11b integrins-ligand complex clusterization inside the granulocyte membrane surface (orange-color membrane). These clusters elicit the recruitment of talin-2 and kindlin-3, which bind to the cytosolic regions of integrins. Talin-2 and kindlin-3 also associate with the F-actin fibers, thus activating the accumulation of F-actin filaments tight to the clusters. Through the Arp2/3 complexes, the F-actin network extends locally and at the sides of the clusters leading to the formation of F-actin fibers. VASP, Fascins, and BAIAP2 elicit the generation of peculiar tubular membrane structures, whose formation and stability are sustained by actin polymerization via active RhoG, which also leads to the local extension of the actin network by the degradation of GTP into GDP and phosphate (Pi). GDP then interacts with actin monomers (upper left box). At this point, these tubular architectures, guided by the actin network diffusion force, will entrap the cancer cell membrane (green color) and ligands. In parallel, the ligands on the cancer cell membrane detach from the integrins located on the granulocyte membrane. This leads to the spontaneous dissociation of talin-2 and kindlin-3 from integrins and in turn to F-actin decomplexation, with subsequent actin network disaggregation. Concomitantly, the prevalence of inactive RhoG stimulates the GEFs-dependent F-Actin depolymerization and GEFs-guided GTP formation (lower right box), culminating with the exposition of ligand molecules into the granulocyte membrane by sequential membrane fusion events, thus terminating the process of trogocytosis.

Fig 3: Association of integrins to F-actin through talin-2 and kindlin-3 in granulocytes(A) Hypothetical surface model of human integrins CD18 and CD11b associated with F-actin through focal adhesion molecules (Talin-2, Kindlin-3) as an early signal for integrin/ligand stabilization and clusterization within the granulocyte cell membrane. Talin-2 markedly activates Integrin-beta-2 thus increasing the affinity binding of the CD18/CD11b integrins to its ligand on cancer cells (cyan arrow). Actin (ACTC1) monomers (Uniprot code, P68032); talin-2 (Uniprot code, Q9Y4G6); kindlin-3 (Uniprot code, Q86UX7); integrin beta-2 (Uniprot code, P05107); integrin alpha-M (Uniprot code, P11215).(B) 3D stereoscopic computational model showing integrin Alpha-M (RCSB-PDB code: 7P2D) with its C-terminal sequence (cytoplasmic region in panel A) binding the kindlin-3 (RCSB-PDB code: 7C3M) and talin-2 (RCSB-PDB code: 6R9T). These two focal adhesion molecules are in turn stably complexed to an actin homotrimer composed of ACTC1 monomers (RCSB-PDB code: 7LRG). Dashed lines represent the cell membrane separating the extracellular space from the cell cytosol. Upper right box depicts the integrin side view of the model referred to as the actin homotrimer axis. The intermediate and lower right boxes represent the kindlin-3 and talin-2 side views of the model referred to as the same trimer axis. The docking model was obtained via ClusPro processing of the indicated RCSB-PDB codes (© Kozakov et al., 2017).(C) Particular of the integrin-talin association mediated by the cytoplasmic regions of the integrin molecule (pink & purple colors) demonstrating the ability of talin-2 to act as a focal adhesion factor by binding to integrins (RCSB-PDB code: 3G9W).