Role of RhoC in cancer cell migration

Migration is one of the five major behaviors of cells. Although RhoC—a classic member of the Rho gene family—was first identified in 1985, functional RhoC data have only been widely reported in recent years. Cell migration involves highly complex signaling mechanisms, in which RhoC plays an essential role. Cell migration regulated by RhoC—of which the most well-known function is its role in cancer metastasis—has been widely reported in breast, gastric, colon, bladder, prostate, lung, pancreatic, liver, and other cancers. Our review describes the role of RhoC in various types of cell migration. The classic two-dimensional cell migration cycle constitutes cell polarization, adhesion regulation, cell contraction and tail retraction, most of which are modulated by RhoC. In the three-dimensional cell migration model, amoeboid migration is the most classic and well-studied model. Here, RhoC modulates the formation of membrane vesicles by regulating myosin II, thereby affecting the rate and persistence of amoeba-like migration. To the best of our knowledge, this review is the first to describe the role of RhoC in all cell migration processes. We believe that understanding the detail of RhoC-regulated migration processes will help us better comprehend the mechanism of cancer metastasis. This will contribute to the study of anti-metastatic treatment approaches, aiding in the identification of new intervention targets for therapeutic or genetic transformational purposes.

Mechanobiology of microvesicle release, uptake, and microvesicle-mediated activation

Microvesicles are small, membrane-bound vesicles that are shed from the plasma membrane of cells into the extracellular space. Microvesicles contain a variety of cargo not typically thought to be released from cells, including receptor tyrosine kinases, cytosolic signaling proteins, and microRNAs, which are transferred from donor cells to recipient cells. The transfer of microvesicle cargo can result in the transformation of recipient cells thereby supporting disease progression, including modified fibroblast metabolism, epithelial cell contractility, vascular remodeling, and immune cell inflammatory signaling. Additionally, microvesicles are believed to play prominent roles in cell-cell communication and disease progression as they are detected at elevated concentrations in diseased tissues. As microvesicle uptake by recipient cells can modulate cell function to promote disease progression, understanding the mechanisms and mechanosensitivity of microvesicle release, internalization, and the resulting signaling is crucial to fully comprehend their functions in disease. Here, we review recent advances in the understanding of actomyosin-regulated microvesicle biogenesis, microvesicle uptake via pinocytosis, and the resulting cellular transformation. We discuss the effects of altered cell contractility, mode of cell migration, and extracellular matrix compliance on microvesicle signaling, with direct implications in disease progression and identifying future therapeutic targets.

Microglia are continuously activated in the circumventricular organs of mouse brain

Microglia are the primary resident immune cells of the brain parenchyma and transform into the amoeboid form in the "activated state" under pathological conditions from the ramified form in the "resting state" under physiologically healthy conditions. In the present study, we found that microglia in the circumventricular organs (CVOs) of adult mice displayed the amoeboid form with fewer branched cellular processes even under normal conditions; however, those in other brain regions showed the ramified form, which is characterized by well-branched and dendritic cellular processes. Moreover, microglia in the CVOs showed the strong protein expression of the M1 markers CD16/32 and CD86 and M2 markers CD206 and Ym1 without any pathological stimulation. Thus, the present results indicate that microglia in the CVOs of adult mice are morphologically and functionally activated under normal conditions, possibly due to the specialized features of the CVOs, namely, the entry of blood-derived molecules into parenchyma through fenestrated capillaries and the presence of neural stem cells.

Comparative morphology and phagocytic capacity of primary human adult microglia with time-lapse imaging

Microglia provide immune surveillance within the brain and spinal cord. Various microglial morphologies include ramified, amoeboid, and pseudopodic. The link between form and function is not clear, especially for human adult microglia which are limited in availability for study. Here, we examined primary human microglia isolated from normal-appearing white matter. Pseudopodic and amoeboid microglia were effective phagocytes, taking up E. coli bioparticles using ruffled cell membrane sheets and retrograde transport. Pseudopodic and amoeboid microglia were more effective phagocytes as compared to ramified microglia or monocyte-derived dendritic cells. Thus, amoeboid and pseudopodic microglia may both be effective as brain scavengers.

mDia2 and CXCL12/CXCR4 chemokine signaling intersect to drive tumor cell amoeboid morphological transitions

Morphological plasticity in response to environmental cues in migrating cancer cells requires F-actin cytoskeletal rearrangements. Conserved formin family proteins play critical roles in cell shape, tumor cell motility, invasion and metastasis, in part, through assembly of non-branched actin filaments. Diaphanous-related formin-2 (mDia2/Diaph3/Drf3/Dia) regulates mesenchymal-to-amoeboid morphological conversions and non-apoptotic blebbing in tumor cells by interacting with its inhibitor diaphanous-interacting protein (DIP), and disrupting cortical F-actin assembly and bundling. F-actin disruption is initiated by a CXCL12-dependent mechanism. Downstream CXCL12 signaling partners inducing mDia2-dependent amoeboid conversions remain enigmatic. We found in MDA-MB-231 tumor cells CXCL12 induces DIP and mDia2 interaction in blebs, and engages its receptor CXCR4 to induce RhoA-dependent blebbing. mDia2 and CXCR4 associate in blebs upon CXCL12 stimulation. Both CXCR4 and RhoA are required for CXCL12-induced blebbing. Neither CXCR7 nor other Rho GTPases that activate mDia2 are required for CXCL12-induced blebbing. The Rho Guanine Nucleotide Exchange Factor (GEF) Net1 is required for CXCL12-driven RhoA activation and subsequent blebbing. These results reveal CXCL12 signaling, through CXCR4, directs a Net1/RhoA/mDia-dependent signaling hub to drive cytoskeleton rearrangements to regulate morphological plasticity in tumor cells. These signaling hubs may be conserved during normal and cancer cells responding to chemotactic cues.

MMP inhibitor Ilomastat induced amoeboid-like motility via activation of the Rho signaling pathway in glioblastoma cells

Matrix metalloproteinases (MMPs) play the important role in the process of glioblastoma cell invasion through 3D matrices. However, the effects of MMP inhibitors used in the treatment of malignant gliomas are unsatisfactory. The aim of this study was to explore the reason and mechanism by which cells move through the dense extracellular matrix without proteolysis. The results showed that MMP inhibitor (MMPI), Ilomastat, induced glioma cells to have an amoeboid-like morphology with invasive ability. Moreover, the RhoA/Rho kinase (ROCK)/myosin light chain (MLC) signal is involved in the MMPI-induced movement mode switch, and RhoA activation is dependent on P115RhoGEF. Importantly, combined inhibition of MMPs and ROCK enhanced the inhibition invasion function of MMPI and increased survival time in vitro and in vivo. The results suggested that glioma cells with MMPI treatment were able to compensate for the loss of invasive proteolysis-dependent migration capacity by acquiring an amoeboid-like migration mode and indicated that the combined MMP inhibitor and ROCK inhibitor can be used as an attractive antitumor drug candidate for the treatment of GBM.

Increase number of mitochondrion-like organelle in symptomatic Blastocystis subtype 3 due to metronidazole treatment

Blastocystis sp., an intestinal organism is known to cause diarrhea with metronidazole regarded as the first line of treatment despite reports of its resistance. The conflicting reports of variation in drug treatment have been ascribed to subtype differences. The present study evaluated in vitro responses due to metronidazole on ST3 isolated from three symptomatic and asymptomatic patients, respectively. Symptomatic isolates were obtained from clinical patients who showed symptoms such as diarrhea and abdominal bloating. Asymptomatic isolates from a stool survey carried out in a rural area. These patients had no other pathogens other than Blastocystis. Ultrastructural studies using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed drug-treated ST3 from symptomatic patients were irregular and amoebic with surface showing high-convoluted folding when treated with metronidazole. These organisms had higher number of mitochondrion-like organelle (MLO) with prominent cristae. However, the drug-treated ST3 from asymptomatic persons remained spherical in shape. Asymptomatic ST3 showed increase in the size of its central body with the MLO located at the periphery.

Motile Human Neutrophils Sense Ligand Density Over Their Entire Contact Area

Neutrophils are key components of the immune system and motility is central their function during the inflammatory response. We have previously demonstrated that neutrophils are capable of switching their motile phenotype between amoeboid-like and keratocyte-like in response to the ligand density of adhesion molecules (Henry et al. in Int Biol 6:348-356, 2014). In this study, we engineered planar micropatterned surfaces that presented adhesion molecules in local islands of high density, separated by regions largely devoid of ligands. By controlling the geometry of islands we made arrays in which the local (on island) adhesion density was high but the global (multi-island) adhesion density over the entire cell-substrate interface was low. Neutrophils in contact with these island arrays assumed a well-spread and directionally-persistent motile phenotype (keratocyte-like) in contrast to the classical amoeboid morphology they display on uniform fields of high adhesion density. By virtue of our rationally designed substrates, we were able to conclude that neutrophils were integrating the stimulation received across their entire contact interface; furthermore, they were able to mount this whole cell response on the timescale of seconds. This work demonstrates the capacity of adhesive microenvironments to direct the phenotype of cell motility, which has broader implications in physiologic processes such as inflammation and cancer metastasis.

In vivo analysis of the time and spatial activation pattern of microglia in the retina following laser-induced choroidal neovascularization

Microglia play a major role in retinal neovascularization and degeneration and are thus potential targets for therapeutic intervention. In vivo assessment of microglia behavior in disease models can provide important information to understand patho-mechanisms and develop therapeutic strategies. Although scanning laser ophthalmoscope (SLO) permits the monitoring of microglia in transgenic mice with microglia-specific GFP expression, there are fundamental limitations in reliable identification and quantification of activated cells. Therefore, we aimed to improve the SLO-based analysis of microglia using enhanced image processing with subsequent testing in laser-induced neovascularization (CNV). CNV was induced by argon laser in MacGreen mice. Microglia was visualized in vivo by SLO in the fundus auto-fluorescence (FAF) mode and verified ex vivo using retinal preparations. Three image processing algorithms based on different analysis of sequences of images were tested. The amount of recorded frames was limiting the effectiveness of the different algorithms. Best results from short recordings were obtained with a pixel averaging algorithm, further used to quantify spatial and temporal distribution of activated microglia in CNV. Morphologically, different microglia populations were detected in the inner and outer retinal layers. In CNV, the peak of microglia activation occurred in the inner layer at day 4 after laser, lacking an acute reaction. Besides, the spatial distribution of the activation changed by the time over the inner retina. No significant time and spatial changes were observed in the outer layer. An increase in laser power did not increase number of activated microglia. The SLO, in conjunction with enhanced image processing, is suitable for in vivo quantification of microglia activation. This surprisingly revealed that laser damage at the outer retina led to more reactive microglia in the inner retina, shedding light upon a new perspective to approach the immune response in the retina in vivo.

Rho/ROCK pathway inhibition by the CDK inhibitor p27(kip1) participates in the onset of macrophage 3D-mesenchymal migration

Infiltration of macrophages into tissue can promote tumour development. Depending on the extracellular matrix architecture, macrophages can adopt two migration modes: amoeboid migration--common to all leukocytes, and mesenchymal migration--restricted to macrophages and certain tumour cells. Here, we investigate the initiating mechanisms involved in macrophage mesenchymal migration. We show that a single macrophage is able to use both migration modes. Macrophage mesenchymal migration is correlated with decreased activity of Rho/Rho-associated protein kinase (ROCK) and is potentiated when ROCK is inhibited, suggesting that amoeboid inhibition participates in mechanisms that initiate mesenchymal migration. We identify the cyclin-dependent kinase (CDK) inhibitor p27(kip1) (also known as CDKN1B) as a new effector of macrophage 3D-migration. By using p27(kip1) mutant mice and small interfering RNA targeting p27(kip1), we show that p27(kip1) promotes mesenchymal migration and hinders amoeboid migration upstream of the Rho/ROCK pathway, a process associated with a relocation of the protein from the nucleus to the cytoplasm. Finally, we observe that cytoplasmic p27(kip1) is required for in vivo infiltration of macrophages within induced tumours in mice. This study provides the first evidence that silencing of amoeboid migration through inhibition of the Rho/ROCK pathway by p27(kip1) participates in the onset of macrophage mesenchymal migration.

Dock-family exchange factors in cell migration and disease

Dock family proteins are evolutionary conserved exchange factors for the Rho GTPases Rac and Cdc42. There are 11 Dock proteins in mammals, named Dock1 (or Dock180) to Dock11 that play different cellular functions. In particular, Dock proteins regulate actin cytoskeleton, cell adhesion and migration. Not surprisingly, members of the Dock family have been involved in various pathologies, including cancer and defects in the central nervous and immune systems. This review proposes an update of the recent findings regarding the function of Dock proteins, focusing on their role in the control of cell migration and invasion and the consequences in human diseases.