IQGAP1 suppresses TβRII-mediated myofibroblastic activation and metastatic growth in liver
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
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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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 4

TGF-β1 increases IQGAP1/TβRII binding, and IQGAP1 knockdown inhibits lysosomal targeting of TβRII.

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TGF-β1 increases IQGAP1/TβRII binding, and IQGAP1 knockdown inhibits lys...
(A) HSCs that express TβRII-HA were serum starved and stimulated with TGF-β1 for indicated times. Cell lysates were subjected to IP using anti-IQGAP1, and coprecipitated TβRII was detected by WB. Densitometric ratios are shown on the bottom. TGF-β1 increased IQGAP1/TβRII binding. Blots represent 3 independent experiments. (B and C) HSCs that were serum starved and pretreated with cycloheximide (40 μg/ml) for 1 hour were incubated with TGF-β1 at 4°C for ligand/receptor binding. After cells were incubated at 37°C for indicated times, cells were fixed for double IF for HA (green) and LAMP1 (red). IQGAP1 knockdown significantly reduced TβRII in late endosome/lysosomes at both 30 and 60 minutes after TGF-β1 stimulation (arrowheads). Scale bar: 20 μm. **P < 0.01 by ANOVA. n = 6 cells each group. Data represent 3 independent experiments with identical results. (D and E) Cells treated as described in B and C were stained for HA and EEA-1. IQGAP1 knockdown induced the accumulation of TβRII in EEA-1–positive endosomes at both 30 and 60 minutes after TGF-β1 stimulation (arrows). Scale bar: 20 μm. **P < 0.01 by ANOVA. n = 6 cells each group. Data are representative of 3 independent repeats with identical results.