Imaging flow cytometry and GST pulldown assays provide new insights into channel catfish leukocyte immune-type receptor-mediated phagocytic pathways

Selective Regulation of Cytoskeletal Dynamics and Filopodia Formation by Teleost Leukocyte Immune-Type Receptors Differentially Contributes to Target Capture During the Phagocytic Process

“…Therefore, we suspect that recruitment and activation of Vav by Syk would provide the necessary catalyst for Rac 1/2 activation and the stimulation of actin-driven membrane protrusions via the Nck-recruited Wave2. Overall, this predicted model encompasses the minimal machinery required for a constitutive IpLITR 1.1b-dependent deployment of filopodia in the absence of agonist stimulation and is supported by our recent biochemical studies ( 27 , 29 , 45 ). Future work is required to formally establish functional roles for Nck, Syk, Vav, Rac 1/2, and Wave2 during IpLITR 1.1b-mediated triggering responses including filopodia formation.…”

“…This would maintain basal Src-dependent tyrosine phosphorylation of the IpLITR 1.1b CYT region facilitating constitutive coupling of IpLITR 1.1b to select components of the cytoskeletal machinery. Importantly, we also recently showed that Nck is recruited to a consensus interaction motif located in the proximal CYT region of IpLITR 1.1b ( 45 ), which would directly bridge IpLITR 1.1b with the Wave2 complex. In mammalian cells, activation of Wave2 requires state-specific phosphorylation as well as interactions with GTP-bound Rho superfamily proteins, most commonly Rac ( 49 ).…”

“…Our proposed mechanism for target acquisition and engulfment pathways facilitated by IpLITR 1.1b have been described in detail elsewhere ( 28 , 29 , 45 ) and we hypothesized that this likely requires the differential participation of the proximal and distal regions of its CYT in the recruitment and activation of select intracellular effectors ( 45 , 46 ). Specifically, for IpLITR 1.1b to constitutively trigger filopodia formation in RBL-2H3 cells without ligand engagements, this receptor may exist in a primed state, facilitating its basal coupling to effectors of actin dynamics.…”

“…As a result, the assembly of the Nck-Wave2 complex within the proximal CYT region of IpLITR 1.1b would most likely be coupled to the recruitment of cytoplasmic guanine nucleotide exchange factors, including Vav. Our recent biochemical studies showed that Syk is preferentially recruited to the distal region of the IpLITR 1.1b CYT ( 45 ). Therefore, we suspect that recruitment and activation of Vav by Syk would provide the necessary catalyst for Rac 1/2 activation and the stimulation of actin-driven membrane protrusions via the Nck-recruited Wave2.…”

Mechanisms of Fish Macrophage Antimicrobial Immunity

“…However, there are at least five distinct immunoglobulin domain-containing multi-gene receptor families with some structural and signaling motifs seen in the mammalian Fc receptors ( 368 ). Moreover, as members of at least one of this family (LITRs) appear to play roles in phagocytosis ( 369 , 370 ), it is conceivable that members of this, as well as the other receptor families may function as fish phagocytic receptors for antibody-opsonized targets.…”