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Comparative Study
. 2015 Sep;135(9):2258-2265.
doi: 10.1038/jid.2015.140. Epub 2015 Apr 7.

IQGAP1 and IQGAP3 Serve Individually Essential Roles in Normal Epidermal Homeostasis and Tumor Progression

Christine L Monteleon  1 , Andrew McNeal  1 , Elizabeth K Duperret  1 , Seung J Oh  1 , Emily Schapira  1 , Todd W Ridky  2
Affiliations
Comparative Study

IQGAP1 and IQGAP3 Serve Individually Essential Roles in Normal Epidermal Homeostasis and Tumor Progression

Christine L Monteleon et al. J Invest Dermatol. 2015 Sep.

Abstract

IQ motif-containing GTPase-activating protein (IQGAP) scaffolding proteins regulate many essential cellular processes including growth factor receptor signaling, cytoskeletal rearrangement, adhesion, and proliferation and are highly expressed in many cancers. Using genetically engineered human skin tissue in vivo, we demonstrate that diminished, sub-physiologic expression of IQGAP1 or IQGAP3 is sufficient to maintain normal epidermal homeostasis, whereas significantly higher levels are required to support tumorigenesis. To target this tumor-specific IQGAP requirement in vivo, we engineered epidermal keratinocytes to express individual IQGAP protein domains designed to compete with endogenous IQGAPs for effector protein binding. Expression of the IQGAP1-IQ motif decoy domain in epidermal tissue in vivo inhibits oncogenic Ras-driven mitogen-activated protein kinase signaling and antagonizes tumorigenesis, without disrupting normal epidermal proliferation or differentiation. These findings define essential non-redundant roles for IQGAP1 and IQGAP3 in the epidermis and demonstrate the potential of IQGAP antagonism for cancer therapy.

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Conflict of interest statement

Conflict of Interest

The authors state no conflict of interest.

Figures

Figure 1
Figure 1
IQGAP1 and IQGAP3 are highly expressed in normal human epidermis and epidermal squamous cell carcinoma. (a) IQGAP1 and IQGAP3 are multidomain scaffolding proteins with highly homologous structural motifs and the ability to bind a range of cell signaling and cytostructrual molecules. (b) Cryosections of human normal and SCC tissue were prepared for immunofluorescence microscopy of IQGAP1 (green), IQGAP3 (red), and nuclei (blue), scale bar = 100 μm. IQGAP1 is expressed throughout the epidermal compartment of both normal and cancer tissue. IQGAP3 expression is concentrated within the proliferative basal layer. Keratin 5 (red) and Keratin 10 (green) differentiation markers are also shown in both normal and SCC tissue.
Figure 2
Figure 2
Keratinocyte proliferation and mitogenic signaling require low-level expression of both IQGAP1 and IQGAP3. (a) Western analysis of primary human keratinocytes expressing constitutive pGIPZ-mediated shRNA interference (IQ1iMod and IQ3iMod) or pLKO-mediated knockdowns (IQ1iLo and IQ3iLo). (b) Quantification of the residual IQGAP1 and IQGAP3 protein expressions of IQ1iMod, IQ3iMod, IQ1iLo and IQ3iLo keratinocytes. (c) A proliferation assay reveals that a nearly-complete IQGAP knockdown in IQ1iLo and IQ3iLo keratinocytes completely arrests cell growth, while IQ1iMod and IQ3iMod cells proliferate at rates similar to that of the control (means ± SD). (d) Western analysis demonstrates IQ1iLo and IQ3iLo cells express markedly lower levels of both EGFR and p-EGFR compared to control or moderate knockdown cells. There is a corresponding reduction in phospho-ERK in IQ1iLo and IQ3iLo keratinocytes. (Stoll et al.)
Figure 3
Figure 3
Invasive epidermal SCC requires higher IQGAP1 and IQGAP3 expression than normal epidermis. (a) Moderate IQGAP1 and IQGAP3 knockdowns in normal human epidermal xenografts are well tolerated, with no discernable effects on tissue architecture or maintenance in vivo. (b) Moderate knockdowns of IQGAP1 and 3 markedly attenuate invasive SCC development in keratinocytes expressing H-RasG12V and CDK4R24C. Control cancer tissues form thick, hyperplastic, deeply invasive tumors, whereas IQ1iMod and IQ3iMod tissues are minimally hyperplastic, and lack significant invasion, Scale bar = 100 μm.
Figure 4
Figure 4
Exogenous expression of IQGAP1-based decoy peptides alters the relative fitness of keratinocytes in organotypic tissues. (a) A multiplexed, internally-controlled, competition assay was utilized to assess relative cellular fitness of distinct, genetically-engineered keratinocyte populations. Keratinocytes expressing a single IQGAP domain (or luciferase control), were pooled in equal ratios and used to regenerate 3–D organotypic skin tissues. Tissues were either maintained in culture or xenografted onto immunodeficient mice. (b) Expression of individual IQGAP peptides does not adversely affect keratinocyte fitness in normal skin in vivo. However, keratinocytes expressing the IQM domain displayed a fitness disadvantage in tumor tissue. (c) In vitro organotypic cultures using the same cell populations from (b) showed similar selection against IQM expressing cells in Ras-expressing tissue (mean ± SD).
Figure 5
Figure 5
Expression of the IQGAP1-IQM decoy peptide inhibits invasive SCC. (a) IQGAP1-IQM expression does not adversely affect normal epidermis in vivo, scale bar = 100 μm. (b) IQGAP1-IQM expression inhibits keratinocyte proliferation and invasion in Ras-expressing neoplastic skin in vitro, scale bar = 100 μm, and in vivo(c), scale bar = 250 μm. (d) Relative tumor cross-section area of xenograft control versus IQGAP1-IQM SCC tumors. (e) MAPK signaling as indicated by phospho-ERK expression is markedly diminished in the IQM-expressing tissue, scale bar = 100 μm.
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References

    1. Berglund L, Bjorling E, Oksvold P, et al. A genecentric Human Protein Atlas for expression profiles based on antibodies. Molecular & cellular proteomics: MCP. 2008;7:2019–27. - PubMed
    1. Briggs MW, Sacks DB. IQGAP proteins are integral components of cytoskeletal regulation. EMBO reports. 2003;4:571–4. - PMC - PubMed
    1. Brown MD, Sacks DB. Protein scaffolds in MAP kinase signalling. Cellular signalling. 2009;21:462–9. - PMC - PubMed
    1. Chudnovsky Y, Adams AE, Robbins PB, et al. Use of human tissue to assess the oncogenic activity of melanoma-associated mutations. Nature genetics. 2005;37:745–9. - PMC - PubMed
    1. Clark EA, Golub TR, Lander ES, et al. Genomic analysis of metastasis reveals an essential role for RhoC. Nature. 2000;406:532–5. - PubMed

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