Misplaced Pages

#388611

45-445: 387 11848 ENSG00000067560 ENSMUSG00000007815 P61586 Q9QUI0 NM_001313947 NM_001664 NM_016802 NM_001313961 NM_001313962 NP_001300876 NP_001655 NP_001300870.1 NP_001655.1 NP_001300890 NP_001300891 NP_058082 Transforming protein RhoA , also known as Ras homolog family member A ( RhoA ), is a small GTPase protein in

90-470: A GAP results in inactivation of the cognate G-protein. Guanosine nucleotide dissociation inhibitors (GDI) maintain small GTPases in the inactive state. Small GTPases regulate a wide variety of processes in the cell , including growth, cellular differentiation , cell movement and lipid vesicle transport. There are more than a hundred proteins in the Ras superfamily. Based on structure, sequence and function,

135-564: A Rho insert in its primary sequence in the GTPase domain. RhoA contains also four insertion or deletion sites with an extra helical subdomain; these sites are characteristic of many GTPases in the Rho family. Most importantly, RhoA contains two switch regions, Switch I and Switch II, whose conformational states are modified following the activation or inactivation of the protein. Both of these switches have characteristic folding, correspond to specific regions on

180-476: A compensatory relationship between RhoA and RhoC at the level of both their expression and activation, and a reciprocal relationship between RhoA and Rac1 activation. Chronic Myeloid Leukemia (CML), a stem cell disorder that prevents myeloid cells from functioning correctly, has been linked to actin polymerization. Signaling proteins like RhoA, regulate polymerization of actin. Due to differences proteins exhibited between normal and affected neutrocytes, RhoA has become

225-544: A new drug candidate named "Rhosin" was synthesized by researchers at the Cincinnati Children's Hospital, a drug with the full intention to inhibit cancer proliferation and promote nerve cell regeneration. This inhibitor specifically targets Rho GTPases to prevent cell growth related to cancer. When tested on breast cancer cells, Rhosin inhibited growth and the growth of mammary spheres in a dose dependent manner, functioning as targets for RhoA while simultaneously maintaining

270-551: A p53-independent transcriptional mechanism while p27 levels are regulated using effector Rho-associated kinases. Cytokinesis is defined by actomyosin-based contraction. RhoA-dependent diaphanous-related formins (DRFs) localize to the cleavage furrow during cytokinesis while stimulating local actin polymerization by coordinating microtubules with actin filaments at the site of the myosin contractile ring. Differences in effector binding distinguish RhoA amongst other related Ras homologs GTPases. Integrins can modulate RhoA activity depending on

315-580: A result, interference with RhoA has been shown to prevent the androgen regulation of SRF genes. In application, RhoA expression is notably higher in malignant prostate cancer cells compared to benign prostate cells, with elevated RhoA expression being associated with elevated lethality and aggressive proliferation. On the other hand, silencing RhoA lessened androgen-regulated cell viability and handicapped prostate cancer cell migration. RhoA has also been found to be hyper activated in gastric cancer cells; in consequence, suppression of RhoA activity partially reversed

360-458: A result, mutations present in the polarity genes indicate that RhoA is critical for tissue polarity and directed intracellular movement. RhoA is required for processes involving cell development, some of which include outgrowth, dorsal closure, bone formation, and myogenesis. Loss of RhoA function is frequently attributed to failed gastrulation and cell migration inability. In extension, RhoA has been shown to function as an intermediary switch within

405-443: A result, the γ-phosphate is cleaved, and inorganic phosphate (Pi) is released. This step also causes a conformational change in the enzyme that promotes the release of GDP. GDP is involved in intracellular signaling processes functioning as a critical regulator in the activity of GTPases. GTPases act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state. The interconversion between GDP and GTP

450-518: A subunit of its receptor Ng-R. The MEMO1-RhoA-DIAPH1 signaling pathway plays an important role in ERBB2-dependent stabilization of microtubules at the cell cortex. A recent study shows that RhoA-Rho kinase signaling mediates thrombin-induced brain damage. p75NTR serves as a regulator for actin assembly. Ras homolog family member A (RhoA) causes the actin cytoskeleton to become rigid which limits growth cone mobility and inhibits neuronal elongation in

495-540: A tumor suppressive growth factor, is known to regulate growth, differentiation and epithelial transformation in tumorigenesis. Instead of blocking growth, TGF-β1 directly activates RhoA in epithelial cells while blocking its downstream target, p160; as a result, activated RhoA-dependent pathways induce stress fiber formation and subsequent mesenchymal properties . Activated RhoA also participates in regulating transcriptional control over other signal transduction pathways via various cellular factors. RhoA proteins help potentiate

SECTION 10

#1732854698389

540-505: A type of G-protein found in the cytosol that are homologous to the alpha subunit of heterotrimeric G-proteins , but unlike the alpha subunit of G proteins, a small GTPase can function independently as a hydrolase enzyme to bind to and hydrolyze a guanosine triphosphate (GTP) to form guanosine diphosphate (GDP). The best-known members are the Ras GTPases and hence they are sometimes called Ras subfamily GTPases . A typical G-protein

585-515: Is a nucleoside diphosphate . It is an ester of pyrophosphoric acid with the nucleoside guanosine . GDP consists of a pyrophosphate group , a pentose sugar ribose , and the nucleobase guanine . GDP is the product of GTP dephosphorylation by GTPases , e.g., the G-proteins that are involved in signal transduction . GDP is converted into GTP with the help of pyruvate kinase and phosphoenolpyruvate. The hydrolysis of GTP to GDP

630-473: Is active when bound to GTP and inactive when bound to GDP (i.e. when the GTP is hydrolyzed to GDP). The GDP can then be replaced by free GTP. Therefore, a G-protein can be switched on and off. GTP hydrolysis is accelerated by GTPase activating proteins (GAPs), while GTP exchange is catalyzed by guanine nucleotide exchange factors (GEFs). Activation of a GEF typically activates its cognate G-protein, while activation of

675-477: Is believed to act primarily at the rear ( uropod ) of migrating cells to promote detachment, similar to the attachment and detachment process found in the focal adhesion mechanism. Signal transduction pathways regulated via RhoA link plasma membrane receptors to focal adhesion formation and the subsequent activation of relevant actin stress fibers. RhoA directly stimulates actin polymerization through activation of diaphanous-related formins, thereby structurally changing

720-744: Is directly linked with the loss of RhoA activity and illustrates how RhoA participates in the transcriptional control of specific protein expression. RhoA as well as several other members of the Rho family are identified as having roles in the regulation of the cytoskeleton and cell division. RhoA plays a pivotal role in G1 cell cycle progression, primarily through regulation of cyclin D1 and cyclin-dependent kinase inhibitors (p21 and p27) expression. These regulation pathways activate protein kinases, which subsequently modulate transcription factor activity. RhoA specifically suppresses p21 levels in normal and transformed cell lines via

765-516: Is facilitated by GTPase enzymes, which utilize a conserved active site motif known as the GTPase-activating protein (GAP). Initially, a water molecule is coordinated by the active site residues of the GTPase enzyme. The water molecule attacks the γ-phosphate of GTP, leading to the formation of a pentavalent transition state. This transition state is stabilized by interactions with the active site residues, including conserved catalytic residues. As

810-401: Is regarded as a prominent regulatory factor in other functions such as the regulation of cytoskeletal dynamics, transcription, cell cycle progression and cell transformation. The specific gene that encodes RhoA, RHOA , is located on chromosome 3 and consists of four exons, which has also been linked as a possible risk factor for atherothrombolic stroke. Similar to other GTPases, RhoA presents

855-530: Is tightly controlled and serves as a molecular timer for signal transduction pathways. When an extracellular signal triggers the activation of a G-protein coupled receptor (GPCR), the associated G-protein exchanges its bound GDP for GTP, leading to a conformational change and activation of downstream signaling cascades. This activation can stimulate a variety of cellular responses, including modulation of gene expression, cytoskeletal rearrangements, and regulation of enzymatic activities. The hydrolysis of GTP to GDP by

900-629: The Rho family of GTPases that in humans is encoded by the RHOA gene . While the effects of RhoA activity are not all well known, it is primarily associated with cytoskeleton regulation, mostly actin stress fibers formation and actomyosin contractility. It acts upon several effectors. Among them, ROCK1 (Rho-associated, coiled-coil containing protein kinase 1) and DIAPH1 (Diaphanous Homologue 1, a.k.a. hDia1, homologue to mDia1 in mouse, diaphanous in Drosophila ) are

945-519: The GTPase activity of the G-protein restoring the inactive state, thus terminates the signaling event. In a type of intracellular signaling referred to as the Nuclear Import process, cytosolic proteins like alpha and beta importins would bind the nuclear localization sequence that is located within the protein, to which this complex would bind to a nuclear pore complex that allows for translocation into

SECTION 20

#1732854698389

990-422: The Ras superfamily is divided into five main families, (Ras, Rho , Ran , Rab and Arf GTPases). The Ras family itself is further divided into 6 subfamilies: Ras , Ral , Rit , Rap , Rheb , and Rad . Miro is a recent contributor to the superfamily. Each subfamily shares the common core G domain, which provides essential GTPase and nucleotide exchange activity. The surrounding sequence helps determine

1035-518: The Rho family are mostly identical, with the N-terminal containing most of the protein coding for GTP binding and hydrolysis. The C-terminal of RhoA is modified via prenylation , anchoring the GTPase into membranes, which is essential for its role in cell growth and cytoskeleton organization. Key amino acids that are involved in the stabilization and regulation of GTP hydrolysis are conserved in RhoA as Gly14, Thr19, Phe30 and Gln63. Correct localization of

1080-449: The RhoA coil and are uniformly stabilized via hydrogen bonds. The conformations of the Switch domains are modified depending on the binding of either GDP or GTP to RhoA. The nature of the bound nucleotide and the ensuing conformational modification of the Switch domains dictates the ability of RhoA to bind or not with partner proteins (see below). The primary protein sequences of members of

1125-547: The RhoA proteins is heavily dependent on the C-terminus; during prenylation, the anchoring of the prenyl group is essential for the stability, inhibition of and the synthesis of enzymes and proliferation. RhoA is sequestered by dissociation inhibitors (RhoGDIs) which remove the protein from the membrane while preventing its further interaction with other downstream effectors. RhoA acquires both inactive GDP-bound and active GTP-bound conformational states; these states alternate between

1170-419: The actin monomers to filaments. ROCK kinases induce actomyosin-based contractility and phosphorylate TAU and MAP2 involved in regulating myosins and other actin-binding proteins in order to assist in cell migration and detachment. The concerted action of ROCK and Dia is essential for the regulation of cell polarity and organization of microtubules. RhoA also regulates the integrity of the extracellular matrix and

1215-526: The active and inactive states via the exchange of GDP to GTP (conducted simultaneously via guanine nucleotide exchange factors and GTPase activating factor). RhoA is activated primarily by guanine nucleotide exchange factors (GEFs) via phosphorylation; due to large network of overlapping phosphorylation, a multitude of GEFs are utilized to enable specific signaling pathways. These structural arrangements provide interaction sites that can interact with effectors and guanine factors in order to stabilize and signal

1260-647: The association of RhoGDI and p75NTR, thereby suppressing RhoA release and promoting growth cone elongation (inhibiting RhoA actin suppression). RHOA has been shown to interact with: Given that its overexpression is found in many malignancies, RhoA activity has been linked within several cancer applications due to its significant involvement in cancer signaling cascades. Serum response factors (SRFs) are known to mediate androgen receptors in prostate cancer cells, including roles ranging from distinguishing benign from malignant prostate and identifying aggressive disease. RhoA mediates androgen-responsiveness of these SRF genes; as

1305-483: The best described. RhoA, and the other Rho GTPases, are part of a larger family of related proteins known as the Ras superfamily , a family of proteins involved in the regulation and timing of cell division . RhoA is one of the oldest Rho GTPases, with homologues present in the genomes since 1.5 billion years. As a consequence, RhoA is somehow involved in many cellular processes which emerged throughout evolution. RhoA specifically

1350-424: The case of neurons, activation of this pathway results in growth cone collapse, therefore inhibits the growth and repair of neural pathways and axons. Inhibition of this pathway by its various components usually results in some level of improved re-myelination. After global ischemia, hyperbaric oxygen (at least at 3 ATA) appears to partially suppress expression of RhoA, in addition to Nogo protein ( Reticulon 4 ), and

1395-465: The developing nervous system. p75NTR without a ligand bound activates RhoA and limits actin assembly, but neurotrophin binding to p75NTR can inactivate RhoA and promote actin assembly. p75NTR associates with the Rho GDP dissociation inhibitor (RhoGDI) , and RhoGDI associates with RhoA. Interactions with Nogo can strengthen the association between p75NTR and RhoGDI. Neurotrophin binding to p75NTR inhibits

Transforming protein RhoA - Misplaced Pages Continue

1440-495: The extracellular matrix composition and other relevant factors. Similarly, RhoA's stimulation of PKN2 kinase activity regulates cell-cell adhesion through apical junction formation and disassembly. Though RhoA is most easily recognized from its unique contributions in actin-myosin contractility and stress fiber formation, new research has also identified it as a key factor in the mediation of membrane ruffling, lamellae formation and membrane blebbing. A majority of this activity occurs in

1485-427: The functional specificity of the small GTPase, for example the 'Insert Loop', common to the Rho subfamily, specifically contributes to binding to effector proteins such as IQGAP and WASP . The Ras family is generally responsible for cell proliferation, Rho for cell morphology, Ran for nuclear transport and Rab and Arf for vesicle transport. Guanosine diphosphate Guanosine diphosphate , abbreviated GDP ,

1530-561: The hydrolysis of GTP. Activation levels of RhoA and associated GEFs are measured using RhoA and GEF pull down assays that uses Rhotekin and mutant RhoA G17A beads respectively RhoA is primarily involved in these activities: actin organization, myosin contractility, cell cycle maintenance, cellular morphological polarization, cellular development and transcriptional control. RhoA is prevalent in regulating cell shape, polarity and locomotion via actin polymerization, actomyosin contractility, cell adhesion, and microtubule dynamics. In addition, RhoA

1575-705: The integrity of normal cellular processes and normal breast cells. These promising results indicate Rhosin's general effectiveness in preventing breast cancer proliferation via RhoA targeting. RhoA's physiological functions have been linked to the contraction and migration of cells which are manifested as symptoms in both asthma and diabetes (i.e. airflow limitation and hyper-responsiveness, desensitization, etc.). Due to pathophysiological overlap of RhoA and Rho-kinase in asthma, both RhoA and Rho-kinase have become promising new target molecules for pharmacological research to develop alternate forms of treatment for asthma. RhoA and Rho kinase mechanisms have been linked to diabetes due to

1620-438: The key element; further experimentation has also shown that RhoA-inhibiting pathways prevent the overall growth of CML cells. As a result, RhoA has significant potential as a therapeutic target in gene therapy techniques to treating CML. Therefore, RhoA's role in the proliferation of cancer cell phenotypes is a key application that can be applied to targeted cancer therapeutics and the development for pharmaceuticals. In June 2012,

1665-410: The leading edge of cells during migration in coordination with membrane protrusions of breast carcinoma. Molecules act on various receptors, such as NgR1, LINGO1 , p75 , TROY and other unknown receptors (e.g. by CSPGs), which stimulates RhoA. RhoA activates ROCK (RhoA kinase) which stimulates LIM kinase, which then inhibits cofilin , which effectively reorganizes the actin cytoskeleton of the cell. In

1710-421: The loss of corresponding cell-cell adhesions (primarily adherens and tight junctions) required for the migration of epithelial. RhoA's role in signal transduction mediation is also attributed to the establishment of tissue polarity in epidermal structures due to its actin polymerization to coordinate vesicular motion; movement within actin filaments forms webs that move in conjunction with vesicular linear motion. As

1755-549: The nucleus. RanGTPase would bind to the beta importin which removes it from the complex, followed by the removal of the alpha importin which is also bound to the RanGTPase. While bound to the RanGTPase, the importins leave the nucleus where the Ran is hydrolyzed, converting the bound GTP into GDP. Ran-GDP can return the nucleus through its bind to a nuclear transport factor, where a Guanine Nucleotide Exchange Factor Protein can come to catalyze

1800-609: The overall mechanically mediated process of stem cell commitment and differentiation. For example, human mesenchymal stem cells and their differentiation into adipocytes or osteocytes are direct results of RhoA's impact on cell shape, signaling and cytoskeletal integrity. Cell shape acts as the primary mechanical cue that drives RhoA activity and downstream effector ROCK activity to control stem cell commitment and cytoskeletal maintenance. Transforming growth factor (TGF)-mediated pathways that control tumor progression and identity are also frequently noted to be RhoA-dependent mechanisms. TGF-β1,

1845-490: The proliferation phenotype of gastric cancer cells via the down-regulation of the RhoA-mammalian Diaphanous 1 pathway. Doxorubicin has been referred to frequently as a highly-promising anti-cancer drug that is also being utilized in chemotherapy treatments; however, as with nearly all chemotherapeutics, the issue of drug resistance remains. Minimizing or postponing this resistance would the necessary dose to eradicate

Transforming protein RhoA - Misplaced Pages Continue

1890-584: The transcription independent of ternary complex factors when activated while simultaneously modulating subsequent extracellular signal activity. It has also been shown that RhoA mediates serum-, LPA- and AIF4-induced signaling pathways in addition to regulating the transcription of the c-fos promoter, a key component in the formation of the ternary complex producing the serum and ternary factors. RhoA signaling and modulation of actin polymerization also regulates Sox9 expression via controlling transcriptional Sox9 activity. The expression and transcriptional activity of Sox9

1935-709: The tumor, thus diminishing drug toxicity. Subsequent RhoA expression decrease has also been associated with increased sensitivity to doxorubicin and the complete reversion of doxorubicin resistance in certain cells; this shows the resilience of RhoA as a consistent indicator anti-cancer activity. In addition to promoting tumor-suppression activity, RhoA also has inherent impact upon the efficacy of drugs in relation to cancer functionality and could be applied to gene therapy protocols in future research. Protein expression of RhoA has been identified to be significantly higher in testicular tumor tissue than that in nontumor tissue; expression of protein for RhoA, ROCK-I, ROCK-II, Rac1, and Cdc42

1980-480: The up-regulated expression of targets within type 1 and 2 diabetic animals. Inhibition of this pathway prevented and ameliorated pathologic changes in diabetic complications, indicating that RhoA pathway is a promising target for therapeutic development in diabetes treatment Small GTPase Small GTPases ( EC 3.6.5.2 ), also known as small G-proteins , are a family of hydrolase enzymes that can bind and hydrolyze guanosine triphosphate (GTP). They are

2025-730: Was greater in tumors of higher stages than lower stages, coinciding with greater lymph metastasis and invasion in upper urinary tract cancer. Although both RhoA and RhoC proteins comprise a significant part of the Rho GTPases that are linked to promoting the invasive behavior of breast carcinomas, attributing specific functions to these individual members has been difficult. We have used a stable retroviral RNA interference approach to generate invasive breast carcinoma cells (SUM-159 cells) that lack either RhoA or RhoC expression. Analysis of these cells enabled us to deduce that RhoA impedes and RhoC stimulates invasion. Unexpectedly, this analysis also revealed

#388611