ATM and cancer: In addition, there is one report that a pool of inactive miR-34 lacking the 5′-phosphate in cancer cells, including MCF-7 cells, is activated by 5′-end phosphorylation by ATM serine/threonine kinase (ATM) and cleavage and polyadenylation factor I subunit 1 (CLP1) in response to DNA damage, in turn allowing AGO2 loading [27].