Protein was harvested and western blot performed as described (21 (link),22 (link)) using the following antibodies: RRM1 (Cell Signaling #8637, RRID:AB_11217623), STIM1 (Sigma-Aldrich S6197, RRID:AB_1079007), ATF4 (Cell Signaling #11815, RRID:AB_2616025), HA (Roche #3F10, RRID:AB_2314622), GAPDH (Origene #TA802519, RRID:AB_2626378), HSC70 (Santa Cruz #sc-7298, RRID:AB_627761), anti-rabbit IgG (Jackson ImmunoResearch Labs #211-032-171, RRID:AB_2339149) and anti-mouse IgG (Jackson ImmunoResearch Labs #115-035-174, RRID:AB_2338512). Further details are in Supplemental Material and Methods.