ROCK1 Functions as a Suppressor of Inflammatory Cell Migration by Regulating PTEN Phosphorylation and Stability.

Abstract 240

Neutrophils and macrophages are major cellular components of the innate immune response and are recruited rapidly in large numbers to sites of infection. The small family of Rho GTPases and its downstream effectors, Rho kinases (Rho-associated, coiled-coil containing protein kinase) have been implicated in regulating various cellular functions including actin cytoskeleton organization, cell adhesion, and cell motility in non-hematopoietic cells. Rho kinases (ROCK1 and ROCK2) belong to a family of serine/threonine kinases whose role in inflammation is not known. Here we show that deficiency of ROCK1 but not ROCK2 results in increased recruitment of macrophages (3.2 fold, n=8, *p<0.01) and neutrophils (3.4 fold, n=5 *p<0.05) compared to WT controls in an in vivo model of aseptic peritonitis. In vitro, deficiency of ROCK1 in bone marrow derived macrophages shows a significant increase in haptotactic transwell migration in response to M-CSF as well as MCP-1 on fibronectin as well as an increase in migration towards the wounded area in a wound healing assay compared to controls (∼3 fold, n=3, *p<0.005). Consistently, deficiency of ROCK1 in bone marrow derived neutrophils also shows a ∼2.63 fold increase in migration in response to fMLP compared to WT bone marrow derived neutrophils (BMNs) in a chemotactic migration assay. ROCK1 deficient macrophages also demonstrate a ∼2.5 fold increase in adhesion on fibronectin (n=3, *p<0.002). The enhanced migration and adhesion in ROCK1−/− macrophages was observed in spite of comparable expression of F4/80 (WT; 85.63% vs. ROCK1−/−; 88.68%, n=4), α4β1 and α5β1 integrins (WT; 67.49% & 88.2% vs. ROCK1−/−; 71.82 % & 87.09%, n=4), while no significant difference in the phagocytosis of sheep red blood cells was observed between WT and ROCK1−/− macrophages (Phagocytic index: WT; 98% vs. ROCK1−/− 97%, n=3, p>.05). Close examination of the cytoskeleton of ROCK1 deficient macrophages using confocal microscopy revealed more F-actin content on the entire cell surface compared to wildtype controls. Consistently, flow cytometric analysis using Alexa 488-phalloidin staining revealed abundance of F-actin in ROCK1−/− macrophages compared to WT controls (WT; 46.19% vs. ROCK1−/−; 65.23%, n=3, *p<0.05). Furthermore, immunofluorescence imaging of podosomes carried out using anti-vinculin antibody revealed more pronounced and increased podosomes in ROCK1 deficient macrophages compared to WT controls (n=3, *p<0.05). Biochemical analysis of ROCK1−/− macrophages revealed that the enhanced recruitment of ROCK1 deficient macrophages and neutrophils was apparent in spite of normal expression of ROCK2 in ROCK1−/− cells and a 60% reduction in overall ROCK activity. Interestingly, although both ROCK1 and ROCK2 co-immunoprecipitate with PTEN in response to cytokine induced stimulation, only ROCK1 appeared to be essential for PTEN phosphorylation, activation and stability. In the absence of ROCK1, PTEN phosphorylation, its activity and stability were significantly impaired in spite of the presence of ROCK2 (n=3, *p<0.05). Consequently, an increase in the activation of downstream targets of PTEN including AKT, GSK-3β and cyclinD1 was observed in ROCK1 deficient macrophages relative to controls (n=3). Taken together, these studies reveal a biochemical pathway involving ROCK1 and PTEN which is involved in the recruitment of macrophages and neutrophils during acute inflammation. Thus, ROCK1 likely functions as a physiologic regulator of PTEN whose function is to repress excessive recruitment of macrophages and neutrophils during acute inflammation.