Hypoxia-induced proliferation of HeLa cells depends on epidermal growth factor receptor-mediated arginase II induction.

Bhuvana A Setty,Yusen Liu,Natasha Pillay Smiley,Leif D Nelin,Yi Jin,Caitlyn M Pool

doi:10.14814/phy2.13175

Bhuvana A Setty, Yusen Liu + Show 4 more

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https://doi.org/10.14814/phy2.13175

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Abstract

Solid tumors can often be hypoxic in regions, and cancer cells can respond to hypoxia with an increase in proliferation and a decrease in apoptosis, leading to a net increase in viable cell numbers. We have recently found that in an osteosarcoma cell line, hypoxia‐induced proliferation depends on arginase II induction. Epidermal growth factor receptor (EGFR) has been shown to mediate the hypoxia‐induced cellular proliferation in some cancer cell lines. We hypothesized that hypoxia‐induced proliferation of HeLa cells would depend on arginase II induction and that this induction of arginase II would occur through EGFR activation. Exposure of HeLa cells to hypoxia resulted in an upregulation of arginase II mRNA and protein levels, with no effect on arginase I expression. Hypoxia also resulted in significantly greater viable cell numbers than did normoxia. The hypoxia‐induced increase in viable cell numbers was prevented by either a small molecule inhibitor of arginase or siRNA targeting arginase II. Overexpression of arginase II resulted in an increase in viable cell numbers both in normoxia and hypoxia. Hypoxia caused a substantial induction of both epidermal growth factor (EGF) and EGFR. Preventing hypoxia‐induced EGFR expression using siRNA abolished hypoxia‐induced arginase II expression and the increase in viable cell numbers. Treatment with EGF in normoxia not only induced arginase II expression but also resulted in an increase in viable cell numbers. Blocking EGF interactions with EGFR using either an EGF neutralizing antibody or an EGFR antibody prevented the hypoxia‐induced increase in viable cell numbers. These results demonstrate an EGF/EGFR/arginase II pathway that is necessary for hypoxic proliferation in HeLa cells.

Highlights

In studies on neoplastic cells, hypoxia promotes tumor growth rather than apoptosis (Iyer et al 1999), perhaps explaining why hypoxia is associated with a more aggressive phenotype in neoplastic cells and a worse prognosis (Hockel et al 1999)
There was ~2-fold greater arginase II protein levels in the HeLa cells exposed to hypoxia than in those exposed to normoxia for 24 h (Fig. 1D)
The main findings of this study were that in HeLa cells: (1) hypoxia increased arginase II mRNA and protein expression; (2) hypoxia-induced cell proliferation was dependent on arginase II induction; (3) hypoxiainduced Epidermal growth factor receptor (EGFR) expression and inhibiting EGFR activity prevented arginase II induction and proliferation; (4) epidermal growth factor (EGF)-induced arginase II expression and cell proliferation through an EGFR-mediated pathway; and (5) hypoxiainduced EGF expression and inhibiting EGF-EGFR interaction prevented hypoxia-induced cell proliferation

Summary

Introduction

In studies on neoplastic cells, hypoxia promotes tumor growth rather than apoptosis (Iyer et al 1999), perhaps explaining why hypoxia is associated with a more aggressive phenotype in neoplastic cells and a worse prognosis (Hockel et al 1999). The metabolism of L-arginine by arginase leads to the production of L-ornithine and urea. L-ornithine can be further metabolized to polyamines and proline, which are critical for cell proliferation, differentiation, and tissue repair (Li et al 2001). Low arginine levels in vitro and in vivo arrest the growth of a 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

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