Increased expression of PD-L1 in endometrial cancer stem-like cells is regulated by hypoxia

¹ Shanghai Key Laboratory of Maternal Fetal Medicine, Clinical and Translational Research Centerof Shanghai First Maternity and Infant Hospital, Tongji University School of Medicine, 201204 Shanghai, China

² Department of Pharmacy, Shanghai Pulmonary Hospital, Tongji University School of Medicine, 201204 Shanghai, China

³ Institute of Chinese Materia Medica, Hunan Academy of Chinese Medicine, 410013 Changsha, Hunan, China

^*Correspondence: zenghl155@163.com (Hongliang Zeng); chenguofang@tongji.edu.cn (Guofang Chen)
^† These authors contributed equally.
Academic Editor: Graham Pawelec

Front. Biosci. (Landmark Ed) 2022, 27(1), 23; https://doi.org/10.31083/j.fbl2701023

Submitted: 1 November 2021 | Revised: 13 December 2021 | Accepted: 21 December 2021 | Published: 17 January 2022

This is an open access article under the CC BY 4.0 license.

Abstract

Background: The expression levels of the programmed cell death ligand 1 (PD-L1), known as an immune-inhibitory molecule, are closely associated with cancer stem cell (CSCs) immune escape. Recently, PD-L1 has also been reported to be able to regulate the self-renewal of cancer stem cells. However, The expression and intrinsic role of PD-L1 in endometrial cancer stem-like cell (ECSC) maintenance and its underlying mechanism of action remain unclear. Methods: Using flow cytometry and western blot assays, we have demonstrated that PD-L1 expression is higher in ECSCs derived from endometrial cancer than in nonstem-like cancer cells. Using mouse xenograft assays for ECSC tumorigenicity. Using gene reporter assay for uncovering the regulation mechanism of PD-L1 in the hypoxia. Results: We revealed the high expression levels of PD-L1 in ECSCs and its correlation with self-renewal. We further found that PD-L1 knockdown reduced expression of several pluripotency-related genes (aldehyde dehydrogenase 1 (ALDH1), CD133, OCT4, SOX2, NANOG), impaired ECSC proliferation and undifferentiated colonies and decreased the number of CD133 positive ECSCs and the number of stem-like spheres. Furthermore, we found that PD-L1 knockdown inhibited ECSC tumorigenicity and the PD-L1 induced self-renewal capability of ECSCs was dependent upon hypoxia HIF-1 $\alpha{}$ and HIF-2 $\alpha{}$ activation. Conclusions: These data link ECSC maintenance to PD-L1 expression through hypoxia and suggest a promising target for PD1/PD-L1 immunotherapy.

Keywords

Programmed cell death ligand 1

Endometrial cancer stem-like cells

PD1/PD-L1

Hypoxia

Figures

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Fig. 1.

PD-L1 is crucial for pluripotency in ECSCs. (A) FACS showing the percentage of CD133 positive cells in ECSC ${}^{isk}$ on days 1, 3, 5 and 8. (B) The genes of ALDH1, PD-L1 and PD-L2 were analysised by qRT-PCR in ECSC ${}^{isk}$ . (C) The protein of ALDH1 and PD-L1 were analysised by immunoblotting in ECSC ${}^{isk}$ on different days of day 1, day 2, day 4, day 5 and day 8. (D) The ECSC ${}^{isk}$ Morphology and the ALDH1 and PD-L1 immunofluorescent staining in ECSC ${}^{isk}$ . (E) Immunohistochemical staining for PD-L1 in tumors. Means $\pm{}$ SEM (N = 3). *p $<$ 0.05, **p $<$ 0.01, and ***p $<$ 0.001.

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