TY - JOUR
T1 - Galectin-3 regulates RasGRP4-mediated activation of N-Ras and H-Ras
AU - Shalom-Feuerstein, Ruby
AU - Levy, Ran
AU - Makovski, Victoria
AU - Raz, Avraham
AU - Kloog, Yoel
N1 - Funding Information:
This work was supported in part by grant 2005344 from the United States–Israel Binational Science Foundation (BSF), by the The Wolfson Family Foundation (YK) and by the NIH/NCI grant R37CA046120 (AR). Yoel Kloog is the incumbent of The Jack H. Skirball Chair for Applied Neurobiology. We thank SR Smith for the editorial assistance.
PY - 2008/6
Y1 - 2008/6
N2 - Galectin-3 (Gal-3) is a pleiotropic β-galactoside-binding protein expressed at relatively high levels in human neoplasms. Its carbohydrate recognition domain (CRD) contains a hydrophobic pocket that can accommodate the farnesyl moiety of K-Ras. Binding of K-Ras to Gal-3 stabilizes K-Ras in its active (GTP-bound) state. Gal-3, which does not interact with N-Ras, was nevertheless shown to reduce N-Ras-GTP in BT-549 cells by an unknown mechanism that we explored here. First, comparative analysis of various cancer cell lines (glioblastomas, breast cancer cells and ovarian carcinomas) showed a positive correlation between low N-Ras-GTP/high K-Ras-GTP phenotype and Gal-3 expression levels. Next we found that epidermal growth factor-stimulated GTP loading of N-Ras, but not of K-Ras, is blocked in cells expressing high levels of Gal-3. Activation of Ras guanine nucleotide releasing proteins (RasGRPs) by phorbol 12-myristate 13-acetate (PMA) or downregulation of Gal-3 by Gal-3 shRNA increased the levels of N-Ras-GTP in Gal-3 expressing cells. We further show that the N-terminal domain of Gal-3 interacts with and inhibits RasGRP4-mediated GTP loading on N-Ras and H-Ras proteins. Growth of BT-549 cells stably expressing the Gal-3 N-terminal domain was strongly attenuated. Overall, these experiments demonstrate a new control mechanism of Ras activation in cancer cells whereby the Gal-3 N-terminal domain inhibits activation of N-Ras and H-Ras proteins.
AB - Galectin-3 (Gal-3) is a pleiotropic β-galactoside-binding protein expressed at relatively high levels in human neoplasms. Its carbohydrate recognition domain (CRD) contains a hydrophobic pocket that can accommodate the farnesyl moiety of K-Ras. Binding of K-Ras to Gal-3 stabilizes K-Ras in its active (GTP-bound) state. Gal-3, which does not interact with N-Ras, was nevertheless shown to reduce N-Ras-GTP in BT-549 cells by an unknown mechanism that we explored here. First, comparative analysis of various cancer cell lines (glioblastomas, breast cancer cells and ovarian carcinomas) showed a positive correlation between low N-Ras-GTP/high K-Ras-GTP phenotype and Gal-3 expression levels. Next we found that epidermal growth factor-stimulated GTP loading of N-Ras, but not of K-Ras, is blocked in cells expressing high levels of Gal-3. Activation of Ras guanine nucleotide releasing proteins (RasGRPs) by phorbol 12-myristate 13-acetate (PMA) or downregulation of Gal-3 by Gal-3 shRNA increased the levels of N-Ras-GTP in Gal-3 expressing cells. We further show that the N-terminal domain of Gal-3 interacts with and inhibits RasGRP4-mediated GTP loading on N-Ras and H-Ras proteins. Growth of BT-549 cells stably expressing the Gal-3 N-terminal domain was strongly attenuated. Overall, these experiments demonstrate a new control mechanism of Ras activation in cancer cells whereby the Gal-3 N-terminal domain inhibits activation of N-Ras and H-Ras proteins.
KW - Cancer
KW - Galectin-3
KW - Ras
KW - RasGRP4
UR - http://www.scopus.com/inward/record.url?scp=43549094660&partnerID=8YFLogxK
U2 - 10.1016/j.bbamcr.2008.03.009
DO - 10.1016/j.bbamcr.2008.03.009
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AN - SCOPUS:43549094660
SN - 0167-4889
VL - 1783
SP - 985
EP - 993
JO - Biochimica et Biophysica Acta - Molecular Cell Research
JF - Biochimica et Biophysica Acta - Molecular Cell Research
IS - 6
ER -