关键词： adhesion molecule   catenin   E-cadherin   IQGAP1   lung adenocarcinoma   micropapillary pattern  

摘要： Micropapillary differentiation in adenocarcinomas has recently been associated with poor prognosis because these tumors are more likely to metastasize. However, no clear explanation exists as to why the presence of a micropapillary pattern is associated with metastasis. A case of primary lung adenocarcinoma with a prominent micropapillary pattern is presented here, with special reference to the immunohistochemical expression of the E-cadherin-mediated system and IQGAP1. Histologically, the tumor was diagnosed as a moderately differentiated papillary adenocarcinoma, showing an extensive micropapillary pattern, with intrapulmonary metastases, pulmonary disseminations, lymphovascular invasions, and lymph node metastases. Immunohistochemically, positive staining for the adhesion molecules E-cadherin, alpha-catenin, and beta-catenin was detected in both the micropapillary and non-micropapillary areas, whereas IQGAP1 was detected in the micropapillary, but not in the non-micropapillary, area. The adhesive function of E-cadherin depends on the integrity of the entire cadherin-catenin-actin network, and thus the expression of IQGAP1 may lead to adherens junction disassembly, and consequently, the release of carcinoma cells organizing in a micropapillary pattern. This is the first report to suggest correlation between adenocarcinoma with a micropapillary pattern and the presence of adhesion molecules, and offers an intriguing first glimpse on the role of the micropapillary pattern in the process of metastasis.

关键词： Antigens   CD29   Cell Adhesion   Cell Membrane   Phosphoprotein Phosphatase  

摘要： Serine/threonine protein phosphatase (PP) 2A is thought to dephosphorylate phosphorylated beta 1 integrin to link with actin filaments (F-actin). However, whether PP2A participates in the regulation of F-actin assembly to which beta 1 integrin is anchored is unclear. We report here that the core enzyme of PP2A (PP2A-AC), consisting of the regulatory subunit A (PP2A-A) and the catalytic subunit C (PP2A-C), forms a complex with beta 1 integrin, a small GTPase Rac, and its effector IQGAP1 in non-malignant human mammary epithelial (HME) cells. Treatment of HME cells with okadaic acid (OA), in inhibitor of PP2A, caused cell rounding, reduction in F-actin assembly that links with beta 1 integrin, and dissociation of IQGAP1-bound PP2A-AC from Rac-beta 1 integrin. The dissociation of IQGAP1-PP2A-AC was accompanied by loss of F-actin gelating activity of Rac-beta 1 integrin. In breast cancer MCF-7 cells, which possess PP2A-C but lack PP2A-A, IQGAP1 was not associated with Rac-beta 1 integrin but with PP2A-C, with no distinct F-actin assembly that linked to Rac-beta 1 integrin even before treatment with OA, We therefore propose that PP2A, especially PP2A-A, functions to maintain F-actin assembly to which beta 1 integrin is anchored by recruitment of IQGAP1 to Rac-beta 1 integrin. (c) 2004 Wiley-Liss, Inc.

关键词： ACTOMYOSIN   CANCER treatment   GUANOSINE triphosphatase   BREAST cancer   PHOSPHOPROTEIN phosphatases  

摘要： Serine/threonine protein phosphatase (PP) 2A is thought to dephosphorylate phosphorylated 1 integrin to link with actin filaments (F-actin). However, whether PP2A participates in the regulation of F-actin assembly to which 1 integrin is anchored is unclear. We report here that the core enzyme of PP2A (PP2A-AC), consisting of the regulatory subunit A (PP2A-A) and the catalytic subunit C (PP2A-C), forms a complex with 1 integrin, a small GTPase Rac, and its effector IQGAP1 in non-malignant human mammary epithelial (HME) cells. Treatment of HME cells with okadaic acid (OA), an inhibitor of PP2A, caused cell rounding, reduction in F-actin assembly that links with 1 integrin, and dissociation of IQGAP1-bound PP2A-AC from Rac-1 integrin. The dissociation of IQGAP1-PP2A-AC was accompanied by loss of F-actin gelating activity of Rac-1 integrin. In breast cancer MCF-7 cells, which possess PP2A-C but lack PP2A-A, IQGAP1 was not associated with Rac-1 integrin but with PP2A-C, with no distinct F-actin assembly that linked to Rac-1 integrin even before treatment with OA. We therefore propose that PP2A, especially PP2A-A, functions to maintain F-actin assembly to which 1 integrin is anchored by recruitment of IQGAP1 to Rac-1 integrin. 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

关键词： IQGAP1   Rho-family GTPases   Rac1   Cdc42   cadherin   CLIP-170   APC   cell adhesion   cell polarization  

摘要： The dynamic rearrangement of cell-cell adhesion is one of the major physiological events in tissue development and tumor metastasis. Polarized cell migration, another key event, is a tightly regulated process that occurs during tissue development, chemotaxis and wound healing. Rho-family small GTPases, especially Rac1 and Cdc42, play pivotal roles in these processes through one of their effectors, IQGAP1. Recent studies reveal that IQGAP1 regulates cadherin-mediated cell-cell adhesion both positively and negatively. It captures and stabilizes microtubules through the microtubule binding protein CLIP-170 near the cell cortex, leading to establishment of polarized cell morphology and directional cell migration. Furthermore, Rac1 and Cdc42 link the adenomatous polyposis coli (APC) protein to actin filaments through IQGAP1 at the leading edge and thereby regulate polarization and directional migration.

关键词： PHOSPHORYLATION   PROTEIN kinases   CYTOPLASM   PROTEIN kinase C   EPITHELIAL cells   GLUTAMIC acid   NEUROBLASTOMA  

摘要： In eukaryotic cells IQGAP1 binds to and alters the function of several proteins, including actin, E-cadherin, beta-catenin, Cdc42, and Rac1. Yeast IQGAP1 homologues have an important role in cytoskeletal organization, suggesting that modulation of the cytoskeleton is a fundamental role of IQGAP1. Phosphorylation is a common mechanism by which cells regulate protein function. Here we demonstrate that endogenous IQGAP1 is highly phosphorylated in MCF-7 human breast epithelial cells. Moreover, incubation of cells with phorbol 12-myristate 13-acetate (PMA) stimulated phosphate incorporation into IQGAP1. By using mass spectrometry, Ser-1443 was identified as the major site phosphorylated on IQGAP1 in intact cells treated with PMA. Ser-1441 was also phosphorylated but to a lesser extent. In vitro analysis with purified proteins documented that IQGAP1 is a substrate for protein kinase C epsilon, which catalyzes phosphorylation on Ser-1443. Consistent with these findings, inhibition of cellular protein kinase C via bisindolymaleimide abrogated Ser-1443 phosphorylation in response to PMA. To elucidate the biological sequelae of phosphorylation, Ser-1441 and Ser-1443 were converted either to alanine, to create a non-phosphorylatable construct, or to glutamic acid and aspartic acid, respectively, to generate a phosphomimetic IQGAP1. Although overexpression of wild type IQGAP1 promoted neurite outgrowth in N1E-115 neuroblastoma cells, the nonphosphorylatable IQGAP1 S1441A/S1443A had no effect. In contrast, the S1441E/S1443D mutation markedly enhanced the ability of IQGAP1 to induce neurite outgrowth. Our data disclose that IQGAP1 is phosphorylated at multiple sites in intact cells and that phosphorylation of IQGAP1 will alter its ability to regulate the cytoskeleton of neuronal cells.

关键词： TUMOR-CELL-MIGRATION   LYMPHOMA TRANSMEMBRANE GLYCOPROTEIN   CD44 INTERACTION   ESTROGEN-RECEPTOR   PROTEIN-KINASE   CYCLIN D1   NUCLEAR TRANSLOCATION   MESOTHELIAL CELLS   REGULATEDKINASE   RNA INTERFERENCE  

摘要： In this study, we have examined the interaction of hyaluronan (HA)-CD44 with IQGAP1 (one of the binding partners for the Rho GTPase Cdc42) in *** human ovarian tumor cells. Immunological and biochemical analyses indicated that IQGAP1 (molecular mass of similar to 190 kDa) is expressed in *** cells and that IQGAP1 interacts directly with Cdc42 in a GTP-dependent manner. Both IQGAP1 and Cdc42 were physically linked to CD44 in *** cells following HA stimulation. Furthermore, the HA-CD44-induced Cdc42-IQGAP1 complex regulated cytoskeletal function via a close association with F-actin that led to ovarian tumor cell migration. In addition, the binding of HA to CD44 promoted the association of ERK2 with the IQGAP1 molecule, which stimulated both ERK2 phosphorylation and kinase activity. The activated ERK2 then increased the phosphorylation of both Elk-1 and estrogen receptor-alpha (ER alpha), resulting in Elk-1- and estrogen-responsive element-mediated transcriptional up-regulation. Down-regulation of IQGAP1 (by treating cells with IQGAP1-specific small interfering RNAs) not only blocked IQGAP1 association with CD44, Cdc42, F-actin, and ERK2 but also abrogated HA-CD44-induced cytoskeletal function, ERK2 signaling (e.g. ERK2 phosphorylation/activity, ERK2-mediated Elk-1/ER alpha phosphorylation, and Elk-1/ER alpha-specific transcriptional activation), and tumor cell migration. Taken together, these findings indicate that HA-CD44 interaction with IQGAP1 serves as a signal integrator by modulating Cdc42 cytoskeletal function, mediating Elk-1-specific transcriptional activation, and coordinating "cross-talk" between a membrane receptor ( CD44) and a nuclear hormone receptor (ER alpha) signaling pathway during ovarian cancer progression.

关键词： Intestinal Neoplasms   Mutation   Stomach Neoplasms   Variation (Genetics)  

摘要： IQGAP1 is recognized as a negative regulator of cell-cell adhesion at adherens junctions in several cell types, including gastric mucosal cells. The histopathologic appearance of diffuse gastric carcinoma is defined by non- or poorly cohesive tumor cells, indicating abnormal intercellular adhesion. Hence, we screened 38 gastric cancers for activating point mutations in IQGAP1. In 2 of the 33 diffuse gastric cancers, there was a missense nucleotide change predicted to alter the amino acid sequence in the GAP-related domain, which includes part of the binding site for the activated small G proteins Cdc42 and Rac1. Many intronic IQGAP1 gene changes were observed, and several occurred more frequently in diffuse-type gastric cancers than in intestinal-type gastric cancers. A highly variable pentanucleotide repeat was identified in the final intron of IQGAP1. The most expanded six-repeat sequence was present exclusively in diffuse-type gastric cancers. Additionally, 19 diffuse cases and two intestinal cases exhibited silent coding region nucleotide alterations. Taken together, our results suggest that IQGAP1 coding sequence mutations are not a frequent event in gastric cancer, but do occur in a subset of diffuse-type gastric carcinomas. Additional studies analyzing other proteins involved in cell adhesion may lead to a better molecular understanding of the histopathologic appearance of diffuse gastric cancers. (C) 2004 Wiley-Liss, Inc.

关键词： protein phosphatase 2A   beta 1-integrin   Rae   IQGAP1   F-actin assembly   cell adhesion  

摘要： Assembly of F-actin that links with beta1-integrin during the G1 phase of cell cycle is released from beta1-integrin and disrupted at mitosis. However, it remains unclear how F-actin assembly to which beta1-integrin anchors is cell cycle-dependently regulated. We show that beta1-integrin was co-immunoprecipitated and co-localized with a small GTPase Rac and its effector IQGAP1, along with PP2A-AC, in HME cells during G1. When the cells were accumulated to G2/M, the co-immunoprecipitation or co-localization of IQGAP1 and PP2A-AC with beta1-integrin was lost, leaving Rac bound to beta1-integrin. The dissociated IQGAP1 was co-immunoprecipitated with the concomitantly dissociated PP2A-A and -C, indicating the complex formation among the proteins in G2/M cells. Falling ball viscometric assays revealed that only IQGAP1-bound beta1-integrin-Rac in G1 cells exhibited an enhanced F-actin cross-linking activity. The results suggest that the mitotic loss of F-actin assembly to which beta1-integrin anchors is due to PP2A-mediated dissociation of IQGAP1 from Rac-bound beta1-integrin. (C) 2004 Elsevier Inc. All rights reserved.

关键词： Fyn   IQGAP1   phosphoinositide 3-kinase   podocyte   slit diaphragm  

摘要： Nephrin is a signalling cell-cell adhesion protein of the Ig superfamily and the first identified component of the slit diaphragm that forms the critical and ultimate part of the glomerular ultrafiltration barrier. The extracellular domains of the nephrin molecules form a network of homophilic and heterophilic interactions building the structural scaffold of the slit diaphragm between the podocyte foot processes. The intracellular domain of nephrin is connected indirectly to the actin cytoskeleton, is tyrosine phosphorylated, and mediates signalling from the slit diaphragm into the podocytes. CD2AP, podocin, Fyn kinase, and phosphoinositide 3-kinase are reported intracellular interacting partners of nephrin, although the biological roles of these interactions are unclarified. To characterize the structural properties and protein-protein interactions of the nephrin intracellular domain, we produced a series of recombinant nephrin proteins. These were able to bind all previously identified ligands, although the interaction with CD2AP appeared to be of extremely low stoichiometry. Fyn phosphorylated nephrin proteins efficiently in vitro. This phosphorylation was required for the binding of phosphoinositide 3-kinase, and significantly enhanced binding of Fyn itself. A protein of 190 kDa was found to associate with the immobilized glutathione S-transferase-nephrin. Peptide mass fingerprinting and amino acid sequencing identified this protein as IQGAP1, an effector protein of small GTPases Rac1 and Cdc42 and a putative regulator of cell-cell adherens junctions. IQGAP1 is expressed in podocytes at significant levels, and could be found at the immediate vicinity of the slit diaphragm. However, further studies are needed to confirm the biological significance of this interaction and its occurrence in vivo.