• Archives of Pharmacal Research
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• v.29 no.2
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• pp.113-122
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• 2006

Among the effector molecules connected with the group of cell surface receptors, Ras proteins have essential roles in transducing extracellular signals to diverse intracellular events, by controlling the activities of multiple signaling pathways. For over 20 years since the discovery of Ras proteins, an enormous amount of knowledge has been accumulated as to how the proteins function in overlapping or distinct fashions. The signaling networks they regulate are very complex due to their multiple functions and cross-talks. Much attention has been paid to the pathological role of Ras in tumorigenesis. In particular, human tumors very frequently express Ras proteins constitutively activated by point mutations. Up to date, three members of the Ras family have been identified, namely H-Ras, K-Ras (A and B), and N-Ras. Although these Ras isoforms function in similar ways, many evidences also support the distinct molecular function of each Ras protein. This review summarizes differential functions of Ras and highlights the current view of the distinct signaling network regulated by each Ras for its contribution to the malignant phenotypic conversion of breast epithelial cells. Four issues are addressed in this review: (1) Ras proteins, (2) membrane localization of Ras, (3) effector molecules downstream of Ras, (4) Ras signaling in invasion. In spite of the accumulation of information on the differential functions of Ras, much more remains to be elucidated to understand the Ras-mediated molecular events of malignant phenotypic conversion of cells in a greater detail.

• Molecules and Cells
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• v.20 no.2
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• pp.196-200
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• 2005

The neurofibromatosis type2 (NF2) tumor suppressor gene product, merlin, is structurally related to the ezrin-radixin-moesin (ERM) family of proteins that anchor the actin cytoskeleton to specific membrane proteins and participate in cell signaling. However, the basis of the tumor suppressing activity of merlin is not well understood. Previously, we identified a role of merlin as an inhibitor of the Ras-ERK signaling pathway. Recent studies have suggested that phosphorylation of merlin, as of other ERM proteins, may regulate its function. To determine whether phosphorylation of merlin affects its suppression of Ras-ERK signaling, we generated plasmids expressing full-length merlin with substitutions of serine 518, a potential phosphorylation site. A substitution that mimics constitutive phosphorylation (S518D) abrogated the ability of merlin to suppress effects of the Ras-ERK signaling pathway such as Ras-induced SRE transactivation, Elk-mediated SRE transactivation, Ras-induced ERK phosphorylation and Ras-induced focus formation. On the other hand, an S518A mutant, which mimics nonphosphorylated merlin, acted like wild type merlin. These observations show that mimicking merlin phosphorylation impairs not only growth suppression by merlin but also its inhibitory action on the Ras-ERK signaling pathway.

• BMB Reports
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• v.49 no.7
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• pp.370-375
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• 2016

Ras oncoproteins are small molecular weight GTPases known for their involvement in oncogenesis, which operate in a complex signaling network with multiple effectors. Approximately 25% of human tumors possess mutations in a member of this family. The Raf1/MEK/Erk1/2 pathway is one of the most intensively studied signaling mechanisms. Different levels of regulation account for the inactivation of MAP kinases by MAPK phosphatases in a cell type- and stimuli-dependent manner. In the present study, using three inducible Ras-expressing NIH/3T3 cell lines, we demonstrated that MKP3 upregulation requires the activation of the Erk1/2 pathway, which correlates with the shutdown of this pathway. We also demonstrated, by applying pharmacological inhibitors and effector mutants of Ras, that induction of MKP3 at the protein level is positively regulated by the oncogenic Ras/Raf/MEK/Erk1/2 signaling pathway.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2001.11a
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• pp.107-107
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• 2001

During the last decade, enormous progress has been made on the biological significance of apoptosis. Since ras is among the most central molecule in signaling, we asked if ras regulates apoptotic pathway. We have previously shown that H-ras, but not N-ras, induces an invasiveness and motility in human breast epithelial cells (MCF10A), while both H-ras and N-ras induce transformed phenotype. In this study, we wished to seek a chemopreventive agent that effectively induces apoptosis in H-ras-activated cells. Here we show that capsaicin, the major pungent phytochemical in red pepper, induces caspase 3-involved apoptosis selectively in H-ras activated MCF10A cells while the parental MCF10A cells are not effected. In order to study the molecular mechanisms for the increased sensitivity of H-ras MCF10A cells to capsaicin-induced apoptosis, activation of ras downstream signaling molecules, mitogen-activated protein kinases (MAPKinases), upon capsaicin treatment was investigated. Phosphorylated forms of JNK1 and p38 MAPKinase were prominently increased whereas activated ERK-1/2 was decreased by capsaicin in ras-activated cells. The parental cells did not respond to capsaicin, suggesting that capsaicin selectively induces apoptosis through modulating activities of ras downstream signaling molecules in H-ras-activated cells. Studies using chemical inhibitors (CPT-cAMP, SB203580 and PD98059) and dominant negative constructs of JNKl, p38 and MEK show that activation of JNK1 and p38 MAPKinase, but not ERK-1/2, is critical for ras-mediated apoptosis by capsaicin.

• Molecules and Cells
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• v.26 no.5
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• pp.462-467
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• 2008

TPA is known to cooperate with an activated Ras oncogene in the transformation of rodent fibroblasts, but the biochemical mechanisms responsible for this effect have not been established. In the present study we used c-fos promoter-luciferase constructs as reporters, in transient transfection assays, in NIH3T3 cells to assess the mechanism of this cooperation. We found a marked synergistic interaction between TPA and a transfected v-Ha-ras oncogene in the activation of c-fos promoter and SRE. SRE has binding sites for TCF and SRF. A dominant-negative Ras (ras-N17) inhibited the TPA-Ras synergy by blocking the PKC-MAPK-TCF pathway. Dominant-negative RhoA and Rac1 (but not Cdc42Hs) inhibited the TPA-Ras synergy by blocking the Ras-Rho-SRF signaling pathway. Constitutively active $PKC{\alpha}$ and $PKC{\varepsilon}$ showed synergy with v-Ras. These results suggest that the activation of two distinct pathways such as Ras-Raf-ERK-TCF pathway and Rho-SRF pathway are responsible for the induction of c-fos by TPA and Ras in mitogenic signaling pathways.

• BMB Reports
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• v.41 no.6
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• pp.479-484
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• 2008

In the present study, we demonstrate that ephrin-A5 is able to induce a transient increase of MAP kinase activity in PC12 cells. However, the effects of ephrin-A5 on the MAP kinase signaling pathway are about three-fold less than that of EGF. In addition, we demonstrate that EphA4 is the only Eph member expressed in PC12 cells, and that tyrosine phosphorylation induced by ephrin-A5 treatment is consistent with the magnitude and longevity of MAP kinase activation. Experiments using the Ras dominant negative mutant N17Ras reveal that Ras plays a pivotal role in ephrin-A5-induced MAP kinase activation in PC12 cells. Importantly, we found that the EphA4 receptor is rapidly internalized by endocytosis upon engagement of ephrin-A5, leading to a subsequent reduction in the MAP kinase activation. Together, these data suggest a novel regulatory mechanism of differential Ras-MAP kinase signaling kineticsexhibited by the forward signaling of EphA4 in PC12 cells.

• BMB Reports
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• v.49 no.9
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• pp.455-456
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• 2016

Mutations of APC and KRAS are frequently observed in human colorectal cancers (CRCs) and the Wnt/β-catenin and Ras pathways are consequently activated in a significant proportion of CRC patients. Mutations in these two genes are also known to synergistically induce progression of CRCs. Through a series of studies, we have demonstrated that inhibition of the Wnt/β-catenin signaling pathway negatively regulates Ras stability, therefore, Ras abundance is increased together with β-catenin in both mice and human CRCs harboring adenomatous polyposis coli (APC) mutations. In a recent study, we identified KY1220, a small molecule that simultaneously degrades β-catenin and Ras by inhibition of the Wnt/β-catenin pathway, and obtained its derivative KYA1797K, which has improved activity and solubility. We found that KYA1797K binds the RGS domain of axin and enhances the binding affinity of β-catenin or Ras with the β-catenin destruction complex components, leading to simultaneous destabilization of β-catenin and Ras via GSK3β activation. By using both in vitro and in vivo studies, we showed that KYA1797K suppressed the growth of CRCs harboring APC and KRAS mutations through destabilization of β-catenin and Ras. Therefore, our findings indicate that the simultaneous destabilization of β-catenin and Ras via targeting axin may serve as an effective strategy for inhibition of CRCs.

• BMB Reports
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• v.47 no.12
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• pp.685-690
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• 2014

The Ras/Raf/MEK/Erk signaling pathway is important for regulation of cell growth, proliferation, differentiation, survival, and apoptosis in response to a variety of extracellular stimuli. Lack of Erk MAPK activation is observed in several cancer cells despite active activation of Ras. However, little is known about the modulation of Erk1/2 activity by active Ras. Here, we show that overexpression of active H-Ras (H-RasG12R) in NIH3T3 fibroblasts impaired FGF2-induced Erk1/2 phosphorylation, as compared to wild-type cells. Northern blot analysis revealed that prolonged expression of active Ras increased MAP kinase phosphatase 3 (MKP3) mRNA expression, a negative regulator of Erk MAPK. Inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway abrogated active Ras-induced up-regulation of MKP3 expression, leading to the rescue of Erk1/2 phosphorylation. Our results demonstrated that the Ras/Raf/MEK/Erk signaling cascade is negatively regulated by the PI3K/Aktdependent transcriptional activation of the MKP3 gene.

• BMB Reports
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• v.51 no.5
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• pp.225-229
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• 2018

In humans, hormonal regulation is crucial for the preparation of uterine environment leading to either successful implantation or menstrual cycle. Estrogen is a pivotal female steroid hormone that regulates the uterine dynamics along with progesterone in the estrous and menstrual cycles in humans. Estrogen signals act via nuclear estrogen receptor or membrane-bound receptor. The membrane-bound estrogen receptor plays a crucial role in the rapid response of estrogen in the uterine epithelium. Recently, RASD1 has received attention as a novel signal transducer of estrogen in various systems including female reproductive organs. In this review, we discuss the regulation of estrogen and RASD1 signaling in the uterus and also provide insights into RAS as a novel signaling molecule in repeated implantation failure.

• BMB Reports
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• v.50 no.7
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• pp.355-360
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• 2017

Mutations in Ras GTPase are among the most common genetic alterations in human cancers. Despite extensive research investigating Ras proteins, their functions still remain a challenge over a long period of time. The currently available data suggests that solving the outstanding issues regarding Ras could lead to development of effective drugs that could have a significant impact on cancer treatment. Developing a better understanding of their biochemical properties or modes of action, along with improvements in their pharmacologic profiles, clinical design and scheduling will enable the development of more effective therapies.