关键词： Proteins  

摘要： IQGAP1 contains a number of protein recognition motifs through which it binds to targets. Several in vitro studies have documented that IQGAP1 interacts directly with calmodulin, actin, E-cadherin, beta -catenin, and the small GTPases Cdc42 and Rac. Nevertheless, direct demonstration of in vivo function of mammalian IQGAP1 is limited. Using a novel assay to evaluate in vivo function of IQGAP1, we document here that microinjection of IQGAP1 into early Xenopus embryos generates superficial ectoderm. lesions at late blastula stages. This activity was retained by the mutated variants of IQGAP1 in which the calponin homology domain or the WW domain was deleted. By contrast, deletion of the IQ (IQGAP1-Delta IQ), Ras-GAP-related (IQGAP1-Delta GRD), or C-terminal (IQGAP1-DeltaC) domains abrogated the effect of IQGAP1 on the embryos. None of the latter mutants bound Cdc42, suggesting that the binding of Cdc42 by IQGAP1 is critical for its function. Moreover, overexpression of IQGAP1, but not IQGAP1-Delta GRD, significantly increased the amount of active Cdc42 in embryonic cells. Co-injection of wild type IQGAP1 with dominant negative Cdc42, but not the dominant negative forms of Rac or Rho, blocked the effect of IQGAP1 on embryonic ectoderm. Together these data indicate that the activity of IQGAP1 in embryonic ectoderm. requires Cdc42 function.

关键词： IQGAP1   E-cadherin   catenin   gastric cancer   immuno-histochemistry  

摘要： Down-regulation of E-cadherin function is characteristic of cancer cells and might involve the small C-protein Rho family, including pac I and Cdc42, IQGAP I has been reported to be one of the target proteins of pac I and Cdc42, To elucidate the role of IQGAPI in cancer-cell adhesion, its expression was investigated in 47 cases of human gastric cancer by immunohistochemistry and Western blot upon protein fractionation, especially in comparison with E-cadherin and catenin expression. In the non-cancerous columnar epithelium of the stomach, IQGAPI, as well as E-cadherin/catenin, was expressed at the cell-cell boundary. IQGAP I was frequently observed diffusely in the cytoplasm in intestinal-type tumors (20/22 cases) but was expressed at the cell membrane in diffuse-type tumors (19/25 cases), thus showing significant association with tumor differentiation (p, < 0.01). Interestingly, membranous expression of IQGAP I was inversely correlated with that of E-cadherin ( < 0.05) or alpha -catenin (p < 0.001), These observations were consistent with the Western blot results following protein fractionation. IQGAPI was dominantly expressed in the soluble fraction in differentiated tumors;however, in undifferentiated tumors, it was mostly in the insoluble fraction. In contrast, both E-cadherin and -catenin were detected only in the insoluble fraction. Thus, subcellular localization of IQGAP I from the cytoplasm to the cell membrane was correlated with E-cadherin dysfunction and tumor dedifferentiation in gastric carcinogenesis. (C) 2001 Wiley-Liss, Inc.

摘要： We have previously proposed that IQGAP1, an effector of Rad and Cdc42, negatively regulates cadherin-mediated cell-cell adhesion by interacting with beta -catenin and by causing the dissociation of alpha -catenin from cadherin-beta -catenin-alpha -catenin complexes and that activated Rad and Cdc42 positively regulate cadherin-mediated cell-cell adhesion by inhibiting the interaction of IQGAP1 with beta -catenin. However, it remains to be clarified in which physiological processes the Rac1-Cdc42-IQGAP1 system is involved. We here examined whether the Rac1-IQGAP1 system is involved in the cell-cell dissociation of Madin-Darby canine kidney II cells during 12-O-tetradecanoylphorbol-13-acetate (TPA)- or hepatocyte growth factor (HGF)-induced cell scattering. By using enhanced green fluorescent protein (EGFP)-tagged alpha -catenin, we found that EGFP-alpha -catenin decreased prior to cell-cell dissociation during cell scattering. We also found that the Rac1-GTP level decreased after stimulation with TPA and that the Rac1-IQGAP1 complexes decreased, while the IQGAP1-beta -catenin complexes increased during action of TPA. Constitutively active Rad and IQGAP1 carboxyl terminus, a putative dominant-negative mutant of IQGAP1, inhibited the disappearance of alpha -catenin from sites of cell-cell contact induced by TPA. Taken together, these results indicate that alpha -catenin is delocalized from cell-cell contact sites prior to cell-cell dissociation induced by TPA or HGF and suggest that the Rac1-IQGAP1 system is involved in cell-cell dissociation through alpha -catenin relocalization.

关键词： gastric cancer   15q26   gene amplification   IQGAP1   beta-catenin  

摘要： Our previous comparative genomic hybridization (CGH) study revealed a novel amplified region at 15q26 in two cell lines established from diffuse types of gastric cancer (GC). In this amplified region, FES and IGF1R, known targets on 15q26, were located telomeric to the amplicon in the two cell lines, HSC39 and 40A, suggesting that another tumor-associated gene exists in this region. While screening expressed sequence tags (ESTs) for novel genes in this region, we identified the IQGAP1 amplification. IQGAP1 has been reported to encode a ras GAP-related protein, and its interaction with cadherin and/or beta -catenin induces a dissociation of beta -catenin from the cadherin-catenin complex. one of the mechanisms for cell-cell adhesion. Northern and Western blot analyses revealed that amplification of this gene was accompanied by corresponding increases in mRNA and protein expression. Moreover, immunocytochemical staining showed that overexpressed IQGAP1 accumulated at the membrane, suggesting its colocalization with beta -catenin. Taken together, these findings suggest that IQGAP1 may be one of the target genes in the 15q26 amplicon correlated with a malignant phenotype of gastric cancer cells, such as diffuse and invasive characteristics, through the disruption of E-cadherin-mediated cell-cell adhesion.

关键词： glioma   gene array   cadherin   catenin   IQGAP1   RhoA  

摘要： Transforming growth factor-alpha (TGF-alpha) and its receptor are frequently co-expressed in high-grade astrocytomas, suggesting a role for TCF-alpha autocrine/paracrine loops in the malignant progression of astrocytomas. To identify genes that may be critical in mediating TGF-alpha impact on the malignant progression of astrocytomas, we have used cDNA arrays to investigate TGF-alpha effects on the gene expression profile of U-373 MG glioblastoma cells. We found that in these cells similar to 50% of the TGF-alpha regulated genes code for cell motility/invasion-related proteins. TGF-alpha action on the expression of four of these proteins, alpha -catenin, IQGAP1, RhoA, and cadherin-ll, was further investigated by immunoblotting in four astrocytoma cell lines and in normal astrocytes. The results demonstrate that the effects of TGF-alpha on IQGAP1, alpha -catenin, and RhoA expression are cell-line dependent. On the other hand, under TGF-alpha treatment, cadherin-li expression is consistently decreased in all astrocytoma cell lines tested but is increased in normal astrocytes. In addition, we found that cadherin-ll is consistently down-regulated in astrocytomas versus normal brain tissues. Altogether, these results suggest that the down-regulation of cadherin-ll is a frequent molecular event in the neoplastic transformation of astrocytes and that this down-regulation may be initiated and/or amplified by TGF-alpha autocrine/paracrine loops during tumor progression.