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ral Gene Products and Their Regulation
Published in Juan Carlos Lacal, Frank McCormick, The ras Superfamily of GTPases, 2017
The activity of Ras superfamily members is thought to be controlled by at least two types of proteins. Guanine nucleotide-releasing factors (GRFs) that activate function by promoting the exchange of GTP for bound GDP, and GAPs that inhibit function by accelerating the hydrolysis of GTP.9 GRFs, which may function like hormone receptors that activate G proteins, have been identified for some Ras-related proteins, however, their regulatory role is only now being investigated. In contrast, a growing body of evidence supports the idea that GAPs for Ras (Ras-GAP and NF-1) act as both negative regulators and as components of the downstream target of Ras. For example, a negative regulatory role is consistent with the observation that the GTPase-stimulating activity of GAP decreases after stimulation of T cell by antigen, which is concomitant with an increase in the proportion of Ras bound to GTP.20 Moreover, GAP associates with and becomes tyrosine-phosphorylated by some growth factor receptors.21-22 In response to receptor activation, GAP also associates with two other proteins whose functions are not yet known.23
Guanosine Triphosphate-Binding Proteins
Published in Enrique Pimentel, Handbook of Growth Factors, 2017
The functional properties of Ras proteins are similar but not identical to those of other members of the Ras superfamily of proteins involved in GTP binding and hydrolysis. However, as other members of the superfamily, the Ras proteins are biologically active when they are in the GTP-bound form and inactive when bound to GDP. The molecular switching from the GDP-bound to the GTP-bound form of Ras is accompanied by conformational alterations in two parts of the protein, termed switch I and switch II regions.128 Activation of c-Ras proteins is promoted by extracellular stimuli, including the binding of various growth factors (insulin, IGF-I, EGF, PDGF, NGF) to their cell surface receptors, which are represented by transmembrane proteins with tyrosine kinase activity. A critical step in the activation of c-Ras proteins by growth factors and other extracellular signaling agents is the release of bound GDP and the binding of GTP. This event is facilitated by a specific guanine nucleotide-releasing factor (GNRF or GRF), which in human cells is represented by a 55-kDa protein of 488 amino acids.129 The human protein is homologous to the CDC25 gene product of the yeast S. cerevisiae, which also enhances GDP release, and its gene is localized in human chromosome band 15q2.4.
An updated review on exosomes: biosynthesis to clinical applications
Published in Journal of Drug Targeting, 2021
Sheela Modani, Devendrasingh Tomar, Suma Tangirala, Anitha Sriram, Neelesh Kumar Mehra, Rahul Kumar, Dharmendra Kumar Khatri, Pankaj Kumar Singh
The exosomes contain common and cell-specific proteins from which synthesised such as immature dendritic cells, intestinal epithelial cells, B lymphocytes and other cells [10]. Common proteins such as Rab proteins (Ras superfamily of monomeric G proteins), which may help in their fusion with membranes of other cells and docking of exosomes [11]. The other types of proteins which are commonly present are annexin I, II, V and VI and played a crucial role in membrane fusion and cell dynamics [12,13]. Adhesion molecules [14], apoptosis proteins, heat shock proteins (Hsc73 and Hsc90), tetraspanins (CD9, CD63, CD81 and CD82), GTPases and cytoskeletal proteins (actin, synenin, moesin, albumin) are also present in exosomes of different sources [15]. Exosomes have integrins on the surface which play an important role in exosome’s fusion to specific target cells [16]. Also, these proteins work as cargo for the information transport from one cell to other. The study on all the proteins is in progress to identify the existence of exosomes as biomarkers.
Angioimmunoblastic T-cell lymphoma-like lymphadenopathy in mice transgenic for human RHOA with p.Gly17Val mutation
Published in OncoImmunology, 2020
Gyu Jin Lee, Yukyung Jun, Hae Yong Yoo, Yoon Kyung Jeon, Daekee Lee, Sanghyuk Lee, Jaesang Kim
Yet another major leap was made with the advent of massively parallel sequencing. Recurrent somatic mutations which potentially represent the so-called driver mutations have been reported for various tumors including T-cell lymphomas. Most remarkable for AITL was the isolation of p.Gly17Val mutation in RHOA.10-12RHOA encodes a highly conserved small GTPase belonging to the RAS superfamily and regulates diverse cellular processes including cell survival, cell cycle progression, and cytoskeleton regulation. The mutation, although also found at low frequencies in other T-cell lymphomas, is seen in over 60% of patient samples indicating that RHOA p.Gly17Val is the most specific recurrent ‘driver’ mutation for AITL described to date.10-12 Mechanistically, the mutation, which occurs in the GTP binding domain, leads to inhibition of GTP binding and sequestration of the partner guanine exchange factor. This loss-of-function mutation generates a dominant negative version abrogating wild type RHOA activity thereby potentially compromising the inhibitory signal of RHOA on cell proliferation.10-12
Prognostic value of RASSF1A methylation status in non-small cell lung cancer (NSCLC) patients: A meta-analysis of prospective studies
Published in Biomarkers, 2019
Hao Hu, Yuefei Zhou, Min Zhang, Rui Ding
RASSF1A is a member of RAS association domain family, which contains an RA domain and a C-terminal SARAH protein-protein interaction motif (Donninger et al.2007). RASSF1A has been proven to be a tumour suppressor gene which could influence multiple cellular activities including promotion of apoptosis, cell cycle arrest, and maintenance of genomic stability (Pfeifer and Dammann 2005, Hesson et al.2013). Like other Ras superfamily members, RASSF1A also comprises many guanine nucleotide-binding proteins (G proteins) that are essential to intracellular signal transduction (Fiolka et al.2013). Global DNA hypomethylation and hypermethylation of tumour suppressor genes are among the common epigenetic hallmarks of cancer cells, which can lead to the loss of function of certain tumour suppressor genes and abnormal activation of oncogenes (Hanahan and Weinberg 2011, Herman and Baylin 2003). Previous studies have shown that unlike many other tumour suppressor genes, mutation is relatively rare in RASSF1A, while increased methylation plays an important role in RASSF1A inactivation (Cao et al.2013). In addition, RASSF1A methylation is related to the process of many kinds of cancers, and can be employed as a prognostic indicator for these cancers, such as breast cancer (Kioulafa et al.2009) and thyroid carcinoma (Niu et al.2017).