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IQGAP1-dependent scaffold suppresses RhoA and inhibits airway smooth muscle contraction
Mallar Bhattacharya, … , Xiaozhu Huang, Dean Sheppard
Mallar Bhattacharya, … , Xiaozhu Huang, Dean Sheppard
Published October 1, 2014
Citation Information: J Clin Invest. 2014;124(11):4895-4898. https://doi.org/10.1172/JCI76658.
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Brief Report Pulmonology

IQGAP1-dependent scaffold suppresses RhoA and inhibits airway smooth muscle contraction

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Abstract

The intracellular scaffold protein IQGAP1 supports protein complexes in conjunction with numerous binding partners involved in multiple cellular processes. Here, we determined that IQGAP1 modulates airway smooth muscle contractility. Compared with WT controls, at baseline as well as after immune sensitization and challenge, Iqgap1–/– mice had higher airway responsiveness. Tracheal rings from Iqgap1–/– mice generated greater agonist-induced contractile force, even after removal of the epithelium. RhoA, a regulator of airway smooth muscle contractility, was activated in airway smooth muscle lysates from Iqgap1–/– mice. Likewise, knockdown of IQGAP1 in primary human airway smooth muscle cells increased RhoA activity. Immunoprecipitation studies indicated that IQGAP1 binds to both RhoA and p190A-RhoGAP, a GTPase-activating protein that normally inhibits RhoA activation. Proximity ligation assays in primary airway human smooth muscle cells and mouse tracheal sections revealed colocalization of p190A-RhoGAP and RhoA; however, these proteins did not colocalize in IQGAP1 knockdown cells or in Iqgap1–/– trachea. Compared with healthy controls, human subjects with asthma had decreased IQGAP1 expression in airway biopsies. Together, these data demonstrate that IQGAP1 acts as a scaffold that colocalizes p190A-RhoGAP and RhoA, inactivating RhoA and suppressing airway smooth muscle contraction. Furthermore, our results suggest that IQGAP1 has the potential to modulate airway contraction severity in acute asthma.

Authors

Mallar Bhattacharya, Aparna Sundaram, Makoto Kudo, Jessica Farmer, Previn Ganesan, Amin Khalifeh-Soltani, Mehrdad Arjomandi, Kamran Atabai, Xiaozhu Huang, Dean Sheppard

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Figure 3

IQGAP1 acts as a scaffold that colocalizes p190A-RhoGAP and RhoA.

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IQGAP1 acts as a scaffold that colocalizes p190A-RhoGAP and RhoA.
(A) Co...
(A) Co-immunoprecipitation of IQGAP1 and p190A-RhoGAP in lysates of human airway smooth muscle. (B) Co-immunoprecipitation of IQGAP1 and FLAG in lysates of human airway smooth muscle transfected with Rho-FLAG or GFP control. (C) Association of IQGAP1 with both RhoA and p190A-RhoGAP was also demonstrated by PLA in cultured human airway smooth muscle cells. In the control condition, PLA probes were applied without primary antibody. Nuclei were stained with DAPI. Original magnification, ×63. (D) Spatial association of p190A-RhoGAP and RhoA, tested by PLA in cultured human airway smooth muscle cells with and without IQGAP1 knockdown and seeded at equal density. Nuclei were stained with DAPI. Number of PLA foci per high-power field (hpf) was calculated for 10 images per condition. **P ≤ 0.001. Original magnification, ×63. (E) Spatial association of p190A-RhoGAP and RhoA, tested by PLA in 10-μm mouse tracheal sections. Smooth muscle was stained with anti–α-SMA antibody (red). Number of PLA foci per unit area of smooth muscle is also shown (n = 4 per group). *P ≤ 0.05. Original magnification, ×63. (F) Immunoblots for IQGAP1, α-SMA, and GAPDH were performed for lysates of airway biopsies from separate healthy control and asthmatic human subjects. Bands were measured by densitometry, and IQGAP1 was quantified normalized to α-SMA (n = 4 per group). *P ≤ 0.05.
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