SUMMARY Akt is a central regulator of cell growth. Its activity can be negatively regulated by the phosphatase PHLPP that specifically dephosphorylates the hydrophobic motif of Akt (Ser473 in Akt1). However, how PHLPP is targeted to Akt is not clear. Here we show that FKBP51 (FK506-binding protein 51) acts as a scaffolding protein for Akt and PHLPP and promotes dephosphorylation of Akt. Furthermore, FKBP51 is downregulated in pancreatic cancer tissue samples and several cancer cell lines. Decreased FKBP51 expression in cancer cells results in hyperphosphorylation of Akt and decreased cell death following genotoxic stress. Overall, our findings identify FKBP51 as a negative regulator of the Akt pathway, with potentially important implications for cancer etiology and response to chemotherapy.

p53-binding protein 1 (53BP1) is known to be an important mediator of the DNA-damage response1, with di-methylation of histone H4 lysine 20 (H4K20me2) critical to the recruitment of 53BP1 to double strand breaks (DSBs)2,3. However, it is not clear how 53BP1 is specifically targeted to the sites of DNA damage, since the overall level of H4K20me2 does not seem to increase following DNA damage. It has been proposed that DNA breaks may cause exposure of methylated H4K20 previously buried within the chromosome, however experimental evidence for such a model is lacking. Here we found that H4K20 methylation actually increases locally upon the induction of DSBs and that methylation of H4K20 at DSBs is mediated by the histone methyltransferase (HMT) MMSET (also known as NSD2 or WHSC1). Downregulation of MMSET significantly decreases H4K20 methylation at DSBs and the subsequent accumulation of 53BP1. We further found that the recruitment of MMSET to DSBs requires the γH2AX-MDC1 pathway, specifically the interaction between the MDC1 BRCT domain and phosphorylated Ser102 of MMSET. Thus, we propose that a pathway involving γH2AX-MDC1-MMSET regulates the induction of H4K20 methylation on histones around DSBs which, in turn, facilitates 53BP1 recruitment.

The Hippo pathway is crucial in organ size control and tissue homeostasis, with deregulation leading to cancer. An extracellular nutrition signal, such as glucose, regulates the Hippo pathway activation. However, the mechanisms are still not clear. Here, we found that the Hippo pathway is directly regulated by the hexosamine biosynthesis pathway (HBP) in response to metabolic nutrients. Mechanistically, the core component of Hippo pathway (YAP) is O-GlcNAcylated by O-GlcNAc transferase (OGT) at serine 109. YAP O-GlcNAcylation disrupts its interaction with upstream kinase LATS1, prevents its phosphorylation, and activates its transcriptional activity. And this activation is not dependent on AMPK. We also identified OGT as a YAP-regulated gene that forms a feedback loop. Finally, we confirmed that glucose-induced YAP O-GlcNAcylation and activation promoted tumorigenesis. Together, our data establish a molecular mechanism and functional significance of the HBP in directly linking extracellular glucose signal to the Hippo-YAP pathway and tumorigenesis.

Highlights d Intracellular PD-L1 binds RNA and regulates the RNA stability of DNA damage genes d PD-L1 competes with the RNA exosome to regulate RNA stability globally d PD-L1 is important for proper DNA damage response and repair d The PD-L1 antibody H1A sensitizes tumors to DNA-damaging therapy