Autophagy mediated by arginine depletion activation of the nutrient sensor GCN2 contributes to interferon-γ-induced malignant transformation of primary bovine mammary epithelial cells.

X-J Xia,L-C Lei,Y-Y Che,C-J Ao,L Wang,Y-Y Gao,S Zhao,J-Q Wang,H-J Yang,J Zhang

doi:10.1038/cddiscovery.2015.65

Abstract

Autophagy has been linked to the regulation of both the prevention and progression of cancer. IFN-γ has been shown to induce autophagy in multiple cell lines in vitro. However, whether IFN-γ can induce autophagy and whether autophagy promotes malignant transformation in healthy lactating bovine mammary epithelial cells (BMECs) remain unclear. Here, we provide the first evidence of the correlation between IFN-γ treatment, autophagy and malignant transformation and of the mechanism underlying IFN-γ-induced autophagy and subsequent malignant transformation in primary BMECs. IFN-γ levels were significantly increased in cattle that received normal long-term dietary corn straw (CS) roughage supplementation. In addition, an increase in autophagy was clearly observed in the BMECs from the mammary tissue of cows expressing high levels of IFN-γ. In vitro, autophagy was clearly induced in primary BMECs by IFN-γ within 24 h. This induced autophagy could subsequently promote dramatic primary BMEC transformation. Furthermore, we found that IFN-γ promoted arginine depletion, activated the general control nonderepressible-2 kinase (GCN2) signalling pathway and resulted in an increase in autophagic flux and the amount of autophagy in BMECs. Overall, our findings are the first to demonstrate that arginine depletion and kinase GCN2 expression mediate IFN-γ-induced autophagy that may promote malignant progression and that immunometabolism, autophagy and cancer are strongly correlated. These results suggest new directions and paths for preventing and treating breast cancer in relation to diet.

Highlights

Autophagy is an evolutionarily conserved catabolic process whereby cytoplasmic proteins and organelles are directed to lysosomes for degradation and recycling.[1]
We showed that IFN-γ can induce autophagy in healthy lactating bovine mammary epithelial cells (BMECs) through the activation of the general control nonderepressible-2 kinase (GCN2) signalling pathway
To address whether induction of autophagy in response to IFN-γ exposure was dependent on GCN2, we examined IFN-γ-induced autophagy in BMECs in which GCN2 expression was inhibited by an adenovirus-delivered short hairpin RNA (shRNA) of GCN2 (Figure 6e)

Summary

INTRODUCTION

Autophagy is an evolutionarily conserved catabolic process whereby cytoplasmic proteins and organelles are directed to lysosomes for degradation and recycling.[1]. In the present study, lactating Holstein cows, which have significantly higher, whereas SQSTM1/p62 expression was siga long lactation period, were used as an experimental model and nificantly lower, compared with that in the MF group These data divided into two groups with the same dietary energy demands indicate that autophagy was markedly enhanced in mammary and the same concentrate component but different forage tissues from the CS group. Our findings are the first to demonstrate that arginine depletion and kinase GCN2 expression mediate IFN-γ-induced autophagy, that the ongoing activation of autophagy promotes BMEC transformation and that nutrition, immunometabolism, autophagy and cancer are strongly correlated. These findings may provide new insight for breast cancer prevention and therapy.

RESULTS

DISCUSSION

MATERIALS AND METHODS

Western blot analysis