RhoB affects macrophage adhesion, integrin expression and migration.

Ludwig Institute for Cancer Research, Royal Free and University College School of Medicine, London, UK.
Experimental Cell Research (Impact Factor: 3.37). 11/2007; 313(16):3505-16. DOI: 10.1016/j.yexcr.2007.07.014
Source: PubMed

ABSTRACT Rho GTPases regulate multiple cellular responses, including cell motility and cell cycle progression. The Rho isoform RhoB represses transformation and affects endosomal trafficking, but its effects on cell adhesion and migration have not been investigated in detail. Here we show that RhoB-null macrophages are more rounded than wild-type macrophages on fibronectin and uncoated glass, and have reduced adhesion to ICAM-1 and glass but not fibronectin. This correlated with lower cell surface expression of beta2 and beta3 integrins but not beta1 integrin. RhoB-null cells migrated faster than Wt cells on fibronectin, consistent with their smaller spread area, but slower than Wt cells on glass, reflecting their reduced adhesion. C3 transferase, which inhibits RhoA, RhoB and RhoC, induced cell spreading but this effect was reduced in RhoB-null cells. However, RhoB is not required for assembly of podosomes, which are integrin-based adhesion sites, whereas C3 transferase induced a decrease in podosomes and defects in tail retraction. Since macrophages do not express RhoC, these effects of C3 transferase are due to inhibition of RhoA rather than RhoB. Our results suggest that RhoB affects cell shape and migration by regulating surface integrin levels.

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    ABSTRACT: RhoA is thought to be essential for coordination of the membrane protrusions and retractions required for immune cell motility and directed migration. Whether the subfamily of Rho (Ras homolog) GTPases (RhoA, RhoB and RhoC) is actually required for the directed migration of primary cells is difficult to predict. Macrophages isolated from myeloid-restricted RhoA/RhoB (conditional) double knockout (dKO) mice did not express RhoC and were essentially pan-Rho deficient. Using real-time chemotaxis assays, we found that retraction of the trailing edge was dissociated from advance of the cell body in dKO cells, which developed extremely elongated tails. Surprisingly, velocity (of the cell body) was increased, while chemotactic efficiency was preserved, compared to wild-type (WT) macrophages. Randomly migrating RhoA/RhoB dKO macrophages exhibited multiple small protrusions and developed large branches due to impaired lamellipodial retraction. A mouse model of peritonitis indicated that monocyte/macrophage recruitment was, surprisingly, more rapid in RhoA/RhoB dKO mice than in WT mice. In comparison to dKO cells, the phenotypes of single RhoA or RhoB deficient macrophages were mild due to mutual compensation. Furthermore, genetic deletion of RhoB partially reversed the motility defect of macrophages lacking the RhoGAP (Rho GTPase-activating protein) myosin IXb (Myo9b). In conclusion, the Rho subfamily is not required for front end functions (motility and chemotaxis), although both RhoA and RhoB are involved in pulling up the rear end and resorbing lamellipodial membrane protrusions. Macrophages lacking Rho proteins migrate faster in vitro, which, in the case of the peritoneum, translates to more rapid in vivo monocyte/macrophage recruitment.
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    ABSTRACT: Purpose: A crucial event in lung adenocarcinoma progression is the switch from an aerogenous spread toward an infiltrating tumor. Loss of RhoB expression has been suggested to be critical for lung cancer invasion. Here, we tested RhoB expression as a prognostic biomarker in non-small-cell lung cancer (NSCLC) with a special focus on lepidic pattern. Experimental design: We analyzed RhoB expression using both immunohistochemistry and RT-qPCR in two series of operated patients (n=100 and 48 respectively) and in a series of advanced lepidic adenocarcinoma (n=31) from different hospitals. Next, we examined the role of RhoB in lung cancer progression in transgenic mice that express inducible EGFRL858R crossed with rhob null mice. Results: We identified that loss of RhoB expression was strongly associated with worse survival (p= 0.0001) and progression-free survival (p <0.001) in the first series. We then confirmed these results after multivariate analyses of the second series. In the series of adenocarcinoma with lepidic features issued from a clinical trial (IFCT-0401), we showed that loss of RhoB expression was associated with higher aggressiveness of stage-IV. Lastly we showed that EGFRL858R/rhob+/+ mice developed mainly diffuse lung tumors with a lepidic pattern while EGFRL858R/rhob+/- and EGFRL858R/rhob-/- developed a greater number of tumors, and aggressive adenocarcinomas with invasive properties. Conclusions: We showed that RhoB is not only a strong prognostic factor in NSCLC but it is also critical for the acquisition of an aggressive phenotype of adenocarcinoma.
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    ABSTRACT: Background The Rho GTPase RhoB has been proposed to be a tumor suppressor in cancer and is downregulated in various tumors including prostate. RhoB has different effects on cell migration depending on the cell type and conditions, but the molecular basis for this variability is unclear. RhoB regulates trafficking of membrane receptors and integrins. We have previously shown that RhoB depletion alters focal adhesion dynamics and reduces surface levels of ß1 integrin in PC3 prostate cancer cells, correlating with increased migration speed.ResultsHere we show that RhoB depletion reduces cell-cell adhesion and downregulates E-cadherin levels as well as increasing internalized E-cadherin in DU145 prostate cancer cells. This is accompanied by increased migration speed. RhoB localizes to cell-cell junctions together with E-cadherin in DU145 cells. RhoB depletion also reduces N-cadherin levels in PC3 cells, which do not express E-cadherin.Conclusions These results indicate that RhoB alters migration of cells with cell-cell adhesions by regulating cadherin levels. We propose that the relative contribution of integrins and cadherins to cell migration underlies the variable involvement for RhoB in this process and that the downregulation of RhoB in some epithelial cancers could contribute to the weakening of epithelial cell-cell junction during tumor progression.