Proteasome Inhibition Suppresses KIT-Independent Gastrointestinal Stromal Tumors Via Targeting Hippo/YAP/Cyclin D1 Signaling

Ting Chen,Nan Ni,Wen-Bin Ou,Nacef Bahri,Liangliang Xu,Yuehong Wu,Boshu Sun,Li Yuan

doi:10.3389/fphar.2021.686874

Abstract

Purpose: Gastrointestinal stromal tumors (GISTs) are the most common malignant tumor of mesenchymal origin of the digestive tract. A yet more challenging resistance mechanism involves transition from oncogenic KIT to a new imatinib-insensitive oncogenic driver, heralded by loss of KIT expression. Our recent studies have shown that inhibition of cyclin D1 and Hippo signaling, which are overexpressed in KIT-independent GIST, is accompanied by anti-proliferative and apoptosis-promoting effects. PRKCQ, JUN, and the Hippo/YAP pathway coordinately regulate GIST cyclin D1 expression. Thus, targeting of these pathways could be effective therapeutically for these now untreatable tumors. Methods: Targeting cyclin D1 expression of small molecular drugs was screened by a cell monolayer growth and western blotting. The biologic mechanisms of bortezomib to KIT-independent GISTs were assessed by immunoblotting, qRT-PCR, cell viability, colony growth, cell cycle analysis, apoptosis, migration and invasiveness. Results: In the initial small molecular inhibitor screening in KIT-independent GIST62, we found that bortezomib-mediated inhibition of the ubiquitin-proteasome machinery showed anti-proliferative effects of KIT-independent GIST cells via downregulation of cyclin D1 and induction of p53 and p21. Treatment with proteasome inhibitor, bortezomib, led to downregulation of cyclin D1 and YAP/TAZ and an increase in the cleaved PARP expression in three KIT-independent GIST cell lines (GIST48B, GIST54, and GIST226). Additionally, it induced p53 and p21 expression in GIST48B and GIST54, increased apoptosis, and led to cell cycle G1/G2-phase arrest, decreased cell viability, colony formation, as well as migration and invasiveness in all GIST cell lines. Conclusion: Although our findings are early proof-of-principle, there are signs of a potential effective treatment for KIT-independent GISTs, the data highlight that targeting of cyclin D1 and Hippo/YAP by bortezomib warrants evaluation as a novel therapeutic strategy in KIT-independent GISTs.

Highlights

Most gastrointestinal stromal tumors (GISTs) are driven by activating oncogenic mutations of receptor tyrosine kinase (RTK) KIT/PDGFRA, which provide a compelling therapeutic target, as evidenced by the clinical successes of KIT/PDGFRAinhibition by small molecule therapeutics
A yet more challenging resistance mechanism found in GIST lesions with KIT mutations as they progress clinically involves the transition from KIT to another novel oncogene, which shows strong resistant to these small molecular inhibitors due to the loss of KIT expression (Fletcher et al, 2003; Debiec-Rychter et al, 2005; Tu et al, 2018; Ou et al, 2019)
We demonstrated that overexpressed cyclin D1 plays an oncogenic role in KIT independent GISTs

Summary

Introduction

Most gastrointestinal stromal tumors (GISTs) are driven by activating oncogenic mutations of receptor tyrosine kinase (RTK) KIT/PDGFRA, which provide a compelling therapeutic target, as evidenced by the clinical successes of KIT/PDGFRAinhibition by small molecule therapeutics. The majority of patients with advanced GIST become resistant to tyrosine kinase inhibitor (TKI) due to secondary KIT or PDGFRA mutations (Gebreyohannes et al, 2019; Huang et al, 2020). We demonstrated that overexpressed cyclin D1 plays an oncogenic role in KIT independent GISTs. Active JUN and Hippo/YAP signaling coordinated and induced cyclin D1 overexpression (Ou et al, 2019). These findings highlight inhibition of cyclin D1 or the Hippo pathway as rational therapeutic strategies for KITindependent GIST

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Conclusion