Functional RNA interference (RNAi) screen identifies system A neutral amino acid transporter 2 (SNAT2) as a mediator of arsenic-induced endoplasmic reticulum stress.
Exposure to the toxic metalloid arsenic is associated with diabetes and cancer and causes proteotoxicity and endoplasmic reticulum (ER) stress at the cellular level. Adaptive responses to ER stress are implicated in cancer and diabetes; thus, understanding mechanisms of arsenic-induced ER stress may offer insights into pathogenesis. Here, we identify genes required for arsenite-induced ER stress response in a genome-wide RNAi screen. Using an shRNA library targeting ∼20,000 human genes, together with an ER stress cell model, we performed flow cytometry-based cell sorting to isolate cells with defective response to arsenite. Our screen discovered several genes modulating arsenite-induced ER stress, including sodium-dependent neutral amino acid transporter, SNAT2. SNAT2 expression and activity are up-regulated by arsenite, in a manner dependent on activating transcription factor 4 (ATF4), an important mediator of the integrated stress response. Inhibition of SNAT2 expression or activity or deprivation of its primary substrate, glutamine, specifically suppressed ER stress induced by arsenite but not tunicamycin. Induction of SNAT2 is coincident with the activation of the nutrient-sensing mammalian target of rapamycin (mTOR) pathway, which is at least partially required for arsenite-induced ER stress. Importantly, inhibition of the SNAT2 or the System L transporter, LAT1, suppressed mTOR activation by arsenite, supporting a role for these transporters in modulating amino acid signaling. These findings reveal SNAT2 as an important and specific mediator of arsenic-induced ER stress, and suggest a role for aberrant mTOR activation in arsenic-related human diseases. Furthermore, this study demonstrates the utility of RNAi screens in elucidating cellular mechanisms of environmental toxins.
Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Raymond S
RS
Oh
Wen-Chi
WC
Pan
Abdullah
A
Yalcin
Hong
H
Zhang
Tomás R
TR
Guilarte
Gökhan S
GS
Hotamisligil
David C
DC
Christiani
Quan
Q
Lu
D051701:Activating Transcription Factor 4 / Q000378:metabolism; D026924:Amino Acid Transport System A / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D001151:Arsenic / Q000633:toxicity*; D018053:Arsenites / Q000633:toxicity; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects* / Q000235:genetics*; D004785:Environmental Pollutants / Q000633:toxicity*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D023281:Genomics / Q000379:methods*; D057809:HEK293 Cells; D006801:Humans; D034622:RNA Interference; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
C497109:ATF4 protein, human; D026924:Amino Acid Transport System A; D018053:Arsenites; D004785:Environmental Pollutants; C498797:SLC38A2 protein, human; D051701:Activating Transcription Factor 4; D058570:TOR Serine-Threonine Kinases; C015001:arsenite; D001151:Arsenic