RICH1 inhibits breast cancer stem cell traits through activating kinases cascade of Hippo signaling by competing with Merlin for binding to Amot-p80

Cancer stem cells (CSCs) are regarded as the root of tumor recurrence and distant metastasis, as well as the major cause of resistance to conventional cancer therapies. Elucidating the mechanism of regulating CSCs is of great significance for the development of CSCs-targeting therapy strategies. YAP/TAZ are identified as key regulators of CSCs-related traits on breast cancer cells; however, the upstream regulatory mechanism of Hippo kinases cascade involved in regulating YAP/TAZ remains elusive. In this study, we found that the low expression of RICH1 in breast cancer was associated with poor prognosis. Depletion of RICH1 promoted the stemness and disrupted the normal epithelial architecture of MCF10A cells. Besides, RICH1 inhibited the migration and invasion of breast cancer cells and sensitized these cells to chemotherapeutic drugs. Mechanistically, RICH1 activated the kinases cascade of Hippo signaling via displacing Amot-p80 from the complex with Merlin. Further studies revealed that the deletion of the BAR domain of RICH1 abolished the function of attenuating the binding of Amot-p80 and Merlin, illustrating that the competitive binding to Amot-p80 with Merlin was mediated by the BAR domain of RICH1. In conclusion, our work elucidated the role and molecular mechanism of RICH1 in stemness regulation of breast cancer, and might provide opportunities for CSCs-targeting therapy.

Perspectives for Ezrin and Radixin in Astrocytes: Kinases, Functions and Pathology

Astrocytes are increasingly perceived as active partners in physiological brain function and behaviour. The structural correlations of the glia–synaptic interaction are the peripheral astrocyte processes (PAPs), where ezrin and radixin, the two astrocytic members of the ezrin-radixin-moesin (ERM) family of proteins are preferentially localised. While the molecular mechanisms of ERM (in)activation appear universal, at least in mammalian cells, and have been studied in great detail, the actual ezrin and radixin kinases, phosphatases and binding partners appear cell type specific and may be multiplexed within a cell. In astrocytes, ezrin is involved in process motility, which can be stimulated by the neurotransmitter glutamate, through activation of the glial metabotropic glutamate receptors (mGluRs) 3 or 5. However, it has remained open how this mGluR stimulus is transduced to ezrin activation. Knowing upstream signals of ezrin activation, ezrin kinase(s), and membrane-bound binding partners of ezrin in astrocytes might open new approaches to the glial role in brain function. Ezrin has also been implicated in invasive behaviour of astrocytomas, and glial activation. Here, we review data pertaining to potential molecular interaction partners of ezrin in astrocytes, with a focus on PKC and GRK2, and in gliomas and other diseases, to stimulate further research on their potential roles in glia-synaptic physiology and pathology.

Long isoform of VEGF stimulates cell migration of breast cancer by filopodia formation via NRP1/ARHGAP17/Cdc42 regulatory network

VEGF stimulates endothelial cells as a key molecule in angiogenesis. VEGF also works as a multifunction molecule, which targets a variety of cell members in the tumor microenvironment. We aimed to reveal VEGF-related molecular mechanisms on breast cancer cells. VEGF-knocked-out MDA-MB-231 cells (231 VEGFKOex3 ) showed rounded morphology and shorter perimeter (1.6-fold, p < 0.0001). The 231 VEGFKOex3 cells also showed impaired cell migration (2.6-fold, p = 0.002). Bevacizumab treatment did not induce any change in morphology and mobility. Soluble neuropilin-1 overexpressing MDA-MB-231 cells (231 sNRP1 ) exhibited rounded morphology and shorter perimeter (1.3-fold, p < 0.0001). The 231 sNRP1 cells also showed impaired cell migration (1.7-fold, p = 0.003). These changes were similar to that of 231 VEGFKOex3 cells. As MDA-MB-231 cells express almost no VEGFR, these results indicate that the interaction between NRP1 and long isoform of VEGF containing a NRP-binding domain regulates the morphology and migration ability of MDA-MB-231 cells. Genome-wide gene expression profiling identified ARHGAP17 as one of the target genes in the downstream of the VEGF/NRP1 signal. We also show that VEGF/NRP1 signal controls filopodia formation of the cells by modulating Cdc42 activity via ARHGAP17. Among 1,980 breast cancer cases from a public database, the ratio of VEGF and SEMA3A in primary tumors (n = 450) of hormone-receptor-negative breast cancer is associated with ARHGAP17 expression inversely, and with disease free survival. Altogether, the bevacizumab-independent VEGF/NRP1/ARHGAP17/Cdc42 regulatory network plays important roles in malignant behavior of breast cancer.

Rich1 negatively regulates the epithelial cell cycle, proliferation and adhesion by CDC42/RAC1-PAK1-Erk1/2 pathway

Rich1, a previously identified Rho GTPase-activating protein (RhoGAP), was found to have close relationship with Rho GTPase family members in multiple cellular processes in nervous cells and platelets. But the exact role of Rich1 in epithelial cells remains obscure. The present investigation demonstrated that up-regulation of Rich1 could cause S-phase arrest, proliferation inhibition and adhesion decline with F-actin amount decrease in epithelial cells. Further exploration in hepatocyte HL7702 revealed that overexpression of Rich1 could greatly elevate the intrinsic GTPase activities on both of CDC42 and RAC1 by stimulating GTP hydrolysis, which consequently attenuated the activities of the Rho proteins and the phosphorylation level of those in PAK1-ERK1/2 signaling cascade. While the GAP domain deleted Rich1 variant or silence of endogenous Rich1 expression could not result in any of the biological effects. It is indicated that Rich1, completely different from in other types of cells, might act as a crucial upstream negative regulator via its GAP domain in control of epithelial cell cycle, proliferation and focal adhesion through CDC42/RAC1-PAK1-ERK1/2 signaling pathway and F-actin dynamics.

Ezrin mediates neuritogenesis via down-regulation of RhoA activity in cultured cortical neurons

Neuronal morphogenesis is implicated in neuronal function and development with rearrangement of cytoskeletal organization. Ezrin, a member of Ezrin/Radixin/Moesin (ERM) proteins links between membrane proteins and actin cytoskeleton, and contributes to maintenance of cellular function and morphology. In cultured hippocampal neurons, suppression of both radixin and moesin showed deficits in growth cone morphology and neurite extensions. Down-regulation of ezrin using siRNA caused impairment of netrin-1-induced axon outgrowth in cultured cortical neurons. However, roles of ezrin in the neuronal morphogenesis of the cultured neurons have been poorly understood. In this report, we performed detailed studies on the roles of ezrin in the cultured cortical neurons prepared from the ezrin knockdown (Vil2^kd/kd) mice embryo that showed a very small amount of ezrin expression compared with the wild-type (Vil2^+/+) neurons. Ezrin was mainly expressed in cell body in the cultured cortical neurons. We demonstrated that the cultured cortical neurons prepared from the Vil2^kd/kd mice embryo exhibited impairment of neuritogenesis. Moreover, we observed increased RhoA activity and phosphorylation of myosin light chain 2 (MLC2), as a downstream effector of RhoA in the Vil2^kd/kd neurons. In addition, inhibition of Rho kinase and myosin II rescued the impairment of neuritogenesis in the Vil2^kd/kd neurons. These data altogether suggest a novel role of ezrin in the neuritogenesis of the cultured cortical neurons through down-regulation of RhoA activity.

Exposure of fathead minnows to municipal wastewater effluent affects intracellular signaling pathways in the liver

Municipal wastewater effluent can impact its receiving environment. In the St. Lawrence River, male fish living downstream from Montreal exhibit increased hepatic vitellogenin, intersex, delayed spermatogenesis and altered immune function. Few studies have examined genome-wide effects associated with municipal effluent exposure in fish to decipher the mechanisms of toxicity. The present objective was to identify hepatic cellular signaling pathways in fathead minnows following exposure to municipal wastewater effluent. Immature minnows were exposed for 21 days to either 0% (Control) or 20% municipal effluent, the highest concentration in the St. Lawrence River. Hepatic RNA was extracted and used to hybridize a fathead minnow oligonucleotide microarray containing approximately 15k gene sequences. A total of 1300 genes were differentially expressed, of which 309 genes had more than 2-fold change in expression level between control and MWWE-exposed fish. Of those, 118 were up-regulated and 191 were down-regulated. Altered genes grouped according to function, indicated effects on various signaling pathways, apoptosis, immune responses, and cellular metabolism. Pathway analysis software predicted at least 5 signaling pathways that were altered by treatment: cell adhesion, inflammation, various kinases, estrogen receptor signaling and WNT signaling. Various components of the canonical Wnt pathway were dramatically down-regulated, while several other genes involved in the non-canonical Wnt pathway, such as Wnt4, LRP6, and PPP2R5E, which are known to inhibit the canonical Wnt pathway, were increased. These results indicate that municipal wastewater effluent from Montreal can target and inhibit various signaling including those implicated in hepatic Wnt signaling pathway in fathead minnows.