Targeting the IDO-BCL2A1-Cytochrome c Pathway Promotes Apoptosis in Oral Squamous Cell Carcinoma

Qiaoping Zheng; Guifang Gan; Xianfu Gao; Qingqiong Luo; Fuxiang Chen

doi:10.2147/OTT.S288692

Targeting the IDO-BCL2A1-Cytochrome c Pathway Promotes Apoptosis in Oral Squamous Cell Carcinoma

Onco Targets Ther. 2021 Mar 4:14:1673-1687. doi: 10.2147/OTT.S288692. eCollection 2021.

Authors

Qiaoping Zheng^#¹, Guifang Gan^#¹, Xianfu Gao², Qingqiong Luo¹, Fuxiang Chen¹

Affiliations

¹ Department of Clinical Immunology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200011, People's Republic of China.
² Shanghai Profleader Biotech Co., Ltd., Shanghai, People's Republic of China.

^# Contributed equally.

Abstract

Purpose: Indolamine 2,3-dioxygenase (IDO) is the rate limiting enzyme of tryptophan degradation and is a negative prognostic factor in oral squamous cell carcinoma (OSCC) patients, while the underlying molecular mechanism remains unclear. This research aimed to explore the IDO expression and its biological functions in OSCC.

Materials and methods: IDO expression was analyzed by qPCR, Western blots, and immunohistochemistry (IHC) in OSCC cell lines and tissue specimens. Tryptophan and kynurenine content were determined by UPLC-MS/MS in serum samples of OSCC patients and healthy controls. Oncomine databases and Kaplan-Meier survival analyses were used to identify the IDO expression and its correlation with OSCC prognosis. Cell counting, CCK8 assay, flow cytometry, cell cycle, and EdU incorporation assays were used to assess the effect of IDO inhibition on OSCC growth either by shRNA or the IDO-specific inhibitor (epacadostat) in vitro. An OSCC xenograft mouse model was established to verify the predicted function of IDO inhibition in vivo. Mechanistically, an 84-gene apoptosis PCR array and rescue experiment were used to characterize the underlying mechanism involved in IDO-regulated apoptosis in OSCC.

Results: IDO expression was upregulated in OSCC cell lines and tissues and was negatively correlated with OSCC progression. Lentivirus-mediated IDO knockdown and epacadostat significantly reduced viability and promoted apoptosis of OSCC cells in vitro and in vivo. The apoptosis PCR array identified BCL2 related protein A1 (BCL2A1) as the most obviously changed gene at the transcriptional level. IDO inhibition downregulated BCL2A1 expression, increased the expression and translocation of cytochrome c, thus promoted apoptosis in OSCC. Overexpression of BCL2A1 reversed the pro-apoptotic effect of IDO inhibition.

Conclusion: The present results revealed that IDO directly affect the growth of OSCC cells by regulating BCL2A1 expression. IDO and the IDO-BCL2A1-cytochrome c axis may be potential therapeutic targets for OSCC.

Keywords: 3-dioxygenase; BCL2A1; apoptosis; indolamine 2; oral squamous cell carcinoma.

Grants and funding

This work was supported by the National Natural Science Foundation of China (81870762) and the Fundamental Research Program Funding of the Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine (JYZZ059, JYZZ043).