Glucose-regulated protein 78 (Grp78) confers chemoresistance to tumor endothelial cells under acidic stress.

Fernanda Visioli,Fernanda Visioli,Fernanda Visioli,Yugang Wang,Jacques E Nör,Jacques E Nör,Pantelis V Rados,Goleeta N Alam,Yugang Wang,Peter J Polverini,Peter J Polverini,Goleeta N Alam,Yu Ning,Yuanpu Peter Di

doi:10.1371/journal.pone.0101053

Abstract

ObjectivesThis study was designed to investigate the activation of the unfolded protein response (UPR) in tumor associated endothelial cells (TECs) and its association with chemoresistance during acidic pH stress.Materials and MethodsEndothelial cells from human oral squamous cell carcinomas (OSCC) were excised by laser capture microdissection (LCM) followed by analysis of UPR markers (Grp78, ATF4 and CHOP) using quantitative PCR. Grp78 expression was also determined by immunostaining. Acidic stress was induced in primary human dermal microvascular endothelial cells (HDMECs) by treatment with conditioned medium (CM) from tumor cells grown under hypoxic conditions or by adjusting medium pH to 6.4 or 7.0 using lactic acid or hydrochloric acid (HCl). HDMEC resistance to the anti-angiogenic drug Sunitinib was assessed with SRB assay.ResultsUPR markers, Grp78, ATF4 and CHOP were significantly upregulated in TECs from OSCC compared to HDMECs. HDMECs cultured in acidic CM (pH 6.0–6.4) showed increased expression of the UPR markers. However, severe acidosis led to marked cell death in HDMECs. Alternatively, HDMECs were able to adapt when exposed to chronic acidosis at pH 7.0 for 7 days, with concomittant increase in Grp78 expression. Chronic acidosis also confers drug resistance to HDMECs against Sunitinib. Knockdown of Grp78 using shRNA resensitizes HDMECs to drug treatment.ConclusionsUPR induction in ECs under acidic pH conditions is related to chemoresistance and may contribute to therapeutic failures in response to chemotherapy. Targeting Grp78, the key component of the UPR pathway, may provide a promising approach to overcome ECs resistance in cancer therapy.

Highlights

Antiangiogenic therapy has emerged as a promising adjuvant approach to cancer treatment
unfolded protein response (UPR) markers, Glucose-Regulated Protein 78 (Grp78), ATF4 and CHOP were significantly upregulated in tumor associated endothelial cells (TECs) from oral squamous cell carcinomas (OSCC) compared to human dermal microvascular endothelial cells (HDMECs)
UPR is activated in the vasculature of human tumors To assess the UPR in tumor associated endothelial cells (TECs) in vivo, laser capture microdissection (LCM) was used to retrieve endothelial cells (EC) lining the blood vessels from human oral squamous cell carcinoma (OSCC) samples (Figure 1A)

Summary

Introduction

Antiangiogenic therapy has emerged as a promising adjuvant approach to cancer treatment. Evidence has shown that tumor associated endothelial cells (TECs) are more resistant to antiangiogenic therapies compared to endothelial cells from normal tissues (NECs) [1]. This resistant phenotype might be acquired by adaptation to stressful conditions in the tumor microenvironment (TME) [2]. A common response of cells to stress in the TME is the activation of the unfolded protein response (UPR), a protective mechanism that cells use to overcome endoplasmic reticulum (ER) stress. Chronic stress requires extended activation of the UPR, which enables cells to adapt and survive [6,7]

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