IQGAP1 suppresses TβRII-mediated myofibroblastic activation and metastatic growth in liver
Chunsheng Liu, … , Vijay H. Shah, Ningling Kang
Chunsheng Liu, … , Vijay H. Shah, Ningling Kang
Published February 1, 2013
Citation Information: J Clin Invest. 2013;123(3):1138-1156. https://doi.org/10.1172/JCI63836.
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Research Article Oncology

IQGAP1 suppresses TβRII-mediated myofibroblastic activation and metastatic growth in liver

Abstract

In the tumor microenvironment, TGF-β induces transdifferentiation of quiescent pericytes and related stromal cells into myofibroblasts that promote tumor growth and metastasis. The mechanisms governing myofibroblastic activation remain poorly understood, and its role in the tumor microenvironment has not been explored. Here, we demonstrate that IQ motif containing GTPase activating protein 1 (IQGAP1) binds to TGF-β receptor II (TβRII) and suppresses TβRII-mediated signaling in pericytes to prevent myofibroblastic differentiation in the tumor microenvironment. We found that TGF-β1 recruited IQGAP1 to TβRII in hepatic stellate cells (HSCs), the resident liver pericytes. Iqgap1 knockdown inhibited the targeting of the E3 ubiquitin ligase SMAD ubiquitination regulatory factor 1 (SMURF1) to the plasma membrane and TβRII ubiquitination and degradation. Thus, Iqgap1 knockdown stabilized TβRII and potentiated TGF-β1 transdifferentiation of pericytes into myofibroblasts in vitro. Iqgap1 deficiency in HSCs promoted myofibroblast activation, tumor implantation, and metastatic growth in mice via upregulation of paracrine signaling molecules. Additionally, we found that IQGAP1 expression was downregulated in myofibroblasts associated with human colorectal liver metastases. Taken together, our studies demonstrate that IQGAP1 in the tumor microenvironment suppresses TβRII and TGF-β dependent myofibroblastic differentiation to constrain tumor growth.

Authors

Chunsheng Liu, Daniel D. Billadeau, Haitham Abdelhakim, Edward Leof, Kozo Kaibuchi, Carmelo Bernabeu, George S. Bloom, Liu Yang, Lisa Boardman, Vijay H. Shah, Ningling Kang

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Figure 2

IQGAP1 C terminus aa 1503–1657 is required for binding and suppressing TβRII.

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IQGAP1 C terminus aa 1503–1657 is required for binding and suppressing T...
(A) Top 4 rows: full-length (FL) IQGAP1 and GST-fused truncated IQGAP1 proteins are shown. Bottom, GST fused truncated IQGAP1 proteins extracted from bacteria were incubated with HSC lysates for GST pull-down assays. Both aa 746–1657 and aa 1503–1657 of IQGAP1 bound to TβRII. Ponceau S staining depicted the purity of the recombinant proteins. (B) Top: after the GST tag of GST-TRII was removed by thrombin treatment, detagged TβRII was incubated with GST-fused IQGAP1 proteins for in vitro binding assays. Both aa 746–1657 and aa 1503–1657 of IQGAP1 bound to TβRII directly in vitro. Ponceau S staining depicted the purity of GST and GST-fused IQGAP1 proteins. Bottom: detagged IQGAP1 aa 746–1657 was incubated with GST or GST-TβRII for in vitro binding assays. GST-TβRII bound to IQGAP1 aa 746-1657 directly in vitro. aa 746–1657 instead of aa 1503–1657 of IQGAP1 was used in this assay because IQGAP1 antibodies could not recognize aa 1503–1657 of IQGAP1. Ponceau S staining depicted the purity of GST and GST fusion proteins. (C) HSCs expressing TβRII-HA were transduced with lentiviruses encoding GFP, IQGAP1-FLAG, or IQGAP1 (1-1502)-FLAG, and subjected to WB. In contrast with IQGAP1, IQGAP1 (1-1502) mutant lacking the TβRII binding region failed to repress TβRII protein levels. Densitometric ratios are shown on the bottom. All data shown represent multiple repeats with similar results.