ATF4 and cancer: In accordance with our observation of mtUPR-mediated enhancement of cancer cell growth by hydrogen, similar mtUPR-mediated effects have been reported in studies irrelevant to hydrogen: (i) phosphorylation of eIf2α [36,37], (ii) increase in ATF4 [37], (iii) activation of ATF5 [38,39], and (iv) activation of HSP60 [40] enhance cancer growth in mammals.