Dataset Information

Conserved sequence repeats of IQGAP1 mediate binding to Ezrin.

ABSTRACT: Mammalian IQGAP proteins all feature multiple ?50 amino acid sequence repeats near their N-termini, and little is known about the function of these "Repeats". We have expressed and purified the Repeats from human IQGAP1 to identify binding partners. We used mass spectrometry to identify 42 mouse kidney proteins that associate with the IQGAP1 Repeats including the ERM proteins ezrin, radixin, and moesin. ERM proteins have an N-terminal FERM domain (4.1, ezrin, radixin, moesin) through which they bind to protein targets and phosphatidylinositol 4,5-bisphosphate (PIP2) and a C-terminal actin-binding domain and function to link the actin cytoskeleton to distinct locations on the cell cortex. Isothermal titration calorimetry (ITC) reveals that the IQGAP1 Repeats directly bind to the ezrin FERM domain, while no binding is seen for full-length "autoinhibited" ezrin or a version of full-length ezrin intended to mimic the activated protein. ITC also indicates that the ezrin FERM domain binds to the Repeats from IQGAP2 but not the Repeats from IQGAP3. We conclude that IQGAP1 and IQGAP2 are positioned at the cell cortex by ERM proteins. We propose that the IQGAP3 Repeats may likewise bind to FERM domains for signaling purposes.

SUBMITTER: Liu J

PROVIDER: S-EPMC3975686 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Conserved sequence repeats of IQGAP1 mediate binding to Ezrin.

Liu Jing J Guidry Jesse J JJ Worthylake David K DK

Journal of proteome research 20131217 2

Mammalian IQGAP proteins all feature multiple ∼50 amino acid sequence repeats near their N-termini, and little is known about the function of these "Repeats". We have expressed and purified the Repeats from human IQGAP1 to identify binding partners. We used mass spectrometry to identify 42 mouse kidney proteins that associate with the IQGAP1 Repeats including the ERM proteins ezrin, radixin, and moesin. ERM proteins have an N-terminal FERM domain (4.1, ezrin, radixin, moesin) through which they ...[more]

PMID: 24294828

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Project description:Defining the mechanisms that control cell growth and division is crucial to understanding cell homeostasis, which impacts human diseases such as cancer and diabetes. IQGAP1, a widely conserved effector and/or regulator of the GTPase CDC42, is a putative oncoprotein that controls cell proliferation; however, its mechanism in tumorigenesis is unknown. The mechanistic target of rapamycin (mTOR) pathway, the center of cell growth control, is commonly activated in human cancers, but has proved to be an ineffective clinical target because of an incomplete understanding of its mechanisms in cell growth inhibition. Using complementary studies in yeast and mammalian cells, we examined a potential role for IQGAP1 in regulating the negative feedback loop (NFL) of mTOR complex 1 (mTORC1) that controls cell growth. Two-hybrid screens identified the yeast TORC1-specific subunit Tco89p as an Iqg1p-binding partner, sharing roles in rapamycin-sensitive growth, axial-bud-site selection and cytokinesis, thus coupling cell growth and division. Mammalian IQGAP1 binds mTORC1 and Akt1 and in response to epidermal growth factor (EGF), cells expressing the mTORC1-Akt1-binding region (IQGAP1(IR-WW)) contained attenuated phosphorylated ERK1/2 (ERK1/2-P) activity and inactive glycogen synthase kinase 3α/β (GSK3α/β), which control apoptosis. Interestingly, these cells displayed a high level of Akt1 S473-P, but an attenuated level of the mTORC1-dependent kinase S6K1 T389-P and induced mTORC1-Akt1- and EGF-dependent transformed phenotypes. Moreover, IQGAP1 appears to influence cell abscission and its activity is elevated in carcinoma cell lines. These findings support the hypothesis that IQGAP1 acts upstream on the mTORC1-S6K1→Akt1 NFL and downstream of it, to couple cell growth and division, and thus like a rheostat, regulates cell homeostasis, dysregulation of which leads to tumorigenesis or other diseases. These results could have implications for the development of the next generation of anticancer therapeutics.

Project description:The winged helix protein FOXA2 and the nuclear receptor PPARg are highly conserved, regionally-expressed transcription factors that regulate networks of genes controlling complex metabolic functions. Cistrome analysis for FOXA2 in mouse liver and PPARg in mouse adipocytes has previously produced consensus binding sites that are nearly identical to those used by the factors in human cells. Despite this conservation of the canonical binding motif, we report here that the great majority of specific binding regions for FOXA2 in human liver and for PPARg in human adipocytes are not in the orthologous locations to the mouse genome. Nevertheless, gene-centric analysis reveals strong shared transcription factor occupancy near genes in tissue-specific metabolic pathways that are functionally conserved across species. Genes with only species-specific binding sites fail to show enrichment for these pathways. Thus, the biological functions of transcription factors that control specific metabolic functions are highly shared across species. Two TFs, FOXA2 and PPARg, were studied for genome-wide conservation of binding between mouse and human in specific tissues/cell-types (liver for FOXA2, adipocytes for PPARg). The number of replicates for each TF was chosen to obtain a comparable number of reads between the TFs and species. Human FOXA2 ChIP-seq was performed on two biological replicates of human liver samples, in three technical replicates each. Input DNA was also collected and sequenced from both biological samples. Mouse FOXA2 ChIP-seq was performed on four biological replicates of mouse liver samples. The ChIP and sequencing were repeated on two of these biological replicates to create technical replicates for additional sequence reads. Input DNA was sequenced from three additional mouse livers. Human PPARg ChIP-seq was performed on a human adipocyte cell-line (SGBS) differentiated in two replicate cultures. Input DNA was also collected and sequenced from one culture. Mouse PPARg ChIP-seq was performed on 3T3-L1 cells differentiated into adipocytes in culture in a single replicate, and this sequence data was pooled with existing data previously generated by the same lab, already available in GEO (GSE21314). A standard pool of input DNA sample sequence from multiple mouse tissue was used for analyzing the Mouse PPARg ChIP-seq data.

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Conserved sequence repeats of IQGAP1 mediate binding to Ezrin.

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Conserved sequence repeats of IQGAP1 mediate binding to Ezrin.

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