Regulation of WAVE1 expression in macrophages at multiple levels

Abstract

M-CSF (or CSF-1) controls macrophage lineage development and function. A CSF-1-dependent culture system was established, which monitored the differentiation of CSF-1-responsive macrophage populations over time and upon adherence. Wiskott-Aldrich syndrome protein verprolin homologous (WAVE) proteins are involved in actin reorganization, a process critical to many cell functions. WAVE2 but not WAVE1 has been considered significant for macrophage function. Using the CSF-1-dependent differentiation system, we were able to demonstrate the contrasting regulation of the expression of WAVE1 and WAVE2; the levels of the latter rose over time and as the macrophage population became adherent, although those of the former increased over time but were down-regulated upon adherence. Evidence was obtained that WAVE1 was also cleaved to a novel, 60-kDa fragment by macrophage adherence and by another pathway involving calpain-mediated proteolysis. Mutagenesis studies indicated that cleavage of WAVE1 by calpain results in the removal of the verprolin-homology, cofilin-like, and acidic domain and thus, the loss of WAVE1 activity. We suggest that WAVE1 is also important for macrophage biology and that it could have separate functions to those of WAVE2.

Phosphorylation of CSF-1R Y721 mediates its association with PI3K to regulate macrophage motility and enhancement of tumor cell invasion

“…These induced responses transduce the pleiotropic effects of CSF-1 and require full expression of a wide range of signaling proteins, some of which are only expressed in mature macrophages grown in CSF-1 for up to a week (Martinez et al, 2006). Indeed, cytoskeletal and adhesion regulatory proteins are highly represented in the upregulated gene expression profile of CSF-1-induced BMM differentiation (Dinh et al, 2008). Thus, ectopic expression of the CSF-1R in non-macrophage cell lines cannot be used to examine normal macrophage signaling pathways, including those regulating motility.…”

WAVE1 mediates suppression of phagocytosis by phospholipid-derived DAMPs

“…Data are mean ± SEM of at least duplicate experiments; *P < 0.05; **P < 0.01; ***P < 0.001 versus corresponding control. support this claim: (a) inhibition of PKA and disruption of PKA anchoring suppress OxPL-induced cell spreading and phagocytosis ( Figures 2 and 3); (b) WAVE1 was recently found to be expressed in bone marrow-derived macrophages (20); and (c) gene silencing of WAVE1 or ablation of this AKAP gene in peritoneal macrophages protect against OxPL challenge in situ and in vivo (Figures 4-6). …”

“…Mobilization of cAMP-responsive events is known to suppress receptor-mediated phagocytosis in macrophages (32). Accordingly, pretreatment with pharmacological inhibitors of PKA, including H89 and PKA amide [14][15][16][17][18][19][20][21][22] (33,34), abolished OxPL-induced actin spread ( Figure 2A) and completely abrogated the inhibition of phagocytosis (Figure 2, B and C). However, H89 did increase baseline phagocytosis…”

“…This nonspecific effect was lower for PKA amide [14][15][16][17][18][19][20][21][22] , a more specific inhibitor of PKA than H89, which binds to the catalytic subunit of PKA in the nanomolar range (refs. 35-37 and Figure 2, B versus C).…”

“…In contrast to all other WASP family members, WAVE1 is predominantly known as an A-kinase anchoring protein (AKAP) that contributes to the specificity of PKA by tethering it to Arp2/3 (19). Only recently, WAVE1 was found expressed in bone marrow-derived macrophages, but its function there remained unknown (20).…”