ATF4 and cancer: In the absence of glucose, PEPCK-M gene expression (PCK2) is positively regulated by ATF4 and its role in coping with nutritional stress in tumor cells has been well described and is consistent with the ability of some cancer cell lines, for example non-small cell lung cancer (NSCLC) cells, to withstand glucose limitation, and even proliferate in the presence of other carbon sources such as glutamine [24].