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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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 5

IQGAP1 knockdown inhibits TGF-β1 downregulation of TβRII, TβRII ubiquitination, and the plasma membrane targeting of SMURF1.

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IQGAP1 knockdown inhibits TGF-β1 downregulation of TβRII, TβRII ubiquiti...
(A) Top: HSCs with their cell-surface proteins prelabeled with biotin were incubated with TGF-1 for indicated times and cells were harvested for streptavidin pull-down and TβRII WB to determine internalized TβRII. Bottom: TβRII degradation curves generated by densitometric analysis are shown. IQGAP1 knockdown inhibited TGF-β1 downregulation of cell surface TβRII. Chlo, chloroquine; Tν, half-life of TβRII. Data are representative of multiple independent experiments. Asterisks designate a point where TβRII was down to 50%. (B) HSCs expressing TβRI-FLAG were transduced with lentiviruses encoding either NT shRNA or IQGAP1 shRNA, and TβRI protein levels were detected by Flag WB. IQGAP1 knockdown increased TβRI-Flag in HSCs. n = 3 experiments with similar results. (C) TβRII-HA was precipitated from HSCs by IP using anti-HA; TβRII ubiquitination was detected by WB. IQGAP1 knockdown markedly inhibited TβRII ubiquitination. (D) Double IF for IQGAP1 (red) and SMURF1 (green) revealed that IQGAP1 and SMURF1 colocalized at the periphery plasma membrane in control cells (arrows, upper panels), and that IQGAP1 knockdown reduced the localization of SMURF1 at the plasma membrane (lower panels). Scale bar: 20 μm. (E) TβRII and SMURF1 colocalized at the peripheral plasma membrane (arrowheads, upper panels), and IQGAP1 knockdown reduced TβRII/SMURF1 colocalization at the plasma membrane (lower panels). Scale bar: 20 μm. (F) IQGAP1 knockdown reduced SMURF1 protein levels in HSCs by WB. β-actin WB was used as a loading control. n = 3 independent experiments with identical results.