Phosphorylation of RhoB by CK1 impedes actin stress fiber organization and epidermal growth factor receptor stabilization.
ABSTRACT RhoB is a small GTPase implicated in cytoskeletal organization, EGF receptor trafficking and cell transformation. It is an immediate-early gene, regulated at many levels of its biosynthetic pathway. Herein we show that the serine/threonine protein kinase CK1 phosphorylates RhoB in vitro but not RhoA or RhoC. With the use of specific CK1 inhibitors, IC261 and D4476, we show that the kinase phosphorylates also RhoB in HeLa cells. Mass spectrometry analysis demonstrates that RhoB is monophosphorylated by CK1, in its C-terminal end, on serine 185. The substitution of Ser185 by Ala dramatically inhibited the phosphorylation of RhoB in cultured cells. Lastly we show that the inhibition of CK1 activates RhoB and promotes RhoB dependent actin fiber formation and EGF-R level. Our data provide the first demonstration of RhoB phosphorylation and indicate that this post-translational maturation would be a novel critical mechanism to control the RhoB functions.
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ABSTRACT: RhoGTPases are key signaling molecules regulating main cellular functions such as migration, proliferation, survival, and gene expression through interactions with various effectors. Within the RhoA-related subclass, RhoA and RhoC contribute to several steps of tumor growth, and the regulation of their expression affects cancer progression. Our aim is to investigate their respective contributions to the acquisition of an invasive phenotype by using models of reduced or forced expression. The silencing of RhoC, but not of RhoA, increased the expression of genes encoding tumor suppressors, such as nonsteroidal anti-inflammatory drug-activated gene 1 (NAG-1), and decreased migration and the anchorage-independent growth in vitro. In vivo, RhoC small interfering RNA (siRhoC) impaired tumor growth. Of interest, the simultaneous knockdown of RhoC and NAG-1 repressed most of the siRhoC-related effects, demonstrating the central role of NAG-1. In addition of being induced by RhoC silencing, NAG-1 was also largely up-regulated in cells overexpressing RhoA. The silencing of RhoGDP dissociation inhibitor α (RhoGDIα) and the overexpression of a RhoA mutant unable to bind RhoGDIα suggested that the effect of RhoC silencing is indirect and results from the up-regulation of the RhoA level through competition for RhoGDIα. This study demonstrates the dynamic balance inside the RhoGTPase network and illustrates its biological relevance in cancer progression.Molecular biology of the cell 07/2011; 22(17):3263-75. DOI:10.1091/mbc.E11-01-0020 · 5.98 Impact Factor
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ABSTRACT: Serine/Threonine phosphorylation of the nonstructural protein 5 (NS5) is a conserved feature of flaviviruses, but the identity and function(s) of the responsible kinase(s) remain unknown. Serine 56 in the methyltransferase domain of NS5 can be phosphorylated intracellularly, is conserved in all flaviviruses, and is a critical residue in the catalytic mechanism. A negative charge at this residue inactivates the 2'-0 methyltransferase activity necessary to form a 5' cap structure of the viral RNA. Here we show pharmacologic inhibition of Casein Kinase 1 (CK1) suppresses yellow fever virus (YFV) production. We also demonstrate the alpha isoform of Casein Kinase 1 (CK1alpha), a kinase previously identified as phosphorylating Hepatitis C Virus NS5A protein, also phosphorylates serine 56 of YFV methyltransferase. Overall these results suggest CK1 activity can influence flaviviral replication.Virus Research 02/2009; 141(1):101-4. DOI:10.1016/j.virusres.2009.01.002 · 2.83 Impact Factor
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ABSTRACT: Metastasis is a multistep process that involves the deregulation of oncogenes and tumor suppressors beyond changes required for primary tumor formation. RHOB is known to have tumor suppressor activity, and its knockdown is associated with more aggressive tumors as well as changes in cell shape, migration, and adhesion. This study shows that oncogenic microRNA, miR-21, represses RHOB expression by directly targeting the 3' untranslated region. Loss of miR-21 is associated with an elevation of RHOB in hepatocellular carcinoma cell lines Huh-7 and HepG2 and in the metastatic breast cancer cell line MDA-MB-231. Using in vitro models of distinct stages of metastasis, we showed that loss of miR-21 also causes a reduction in migration, invasion, and cell elongation. The reduction in migration and cell elongation can be mimicked by overexpression of RHOB. Furthermore, changes in miR-21 expression lead to alterations in matrix metalloproteinase-9 activity. Therefore, we conclude that miR-21 promotes multiple components of the metastatic phenotype in vitro by regulating several important tumor suppressors, including RHOB.Molecular Cancer Research 05/2010; 8(5):691-700. DOI:10.1158/1541-7786.MCR-09-0465 · 4.50 Impact Factor