Phospho-epitope binding by the BRCT domains of hPTIP controls multiple aspects of the cellular response to DNA damage

Abstract

Human (h)PTIP plays important but poorly understood roles in cellular responses to DNA damage. hPTIP interacts with 53BP1 tumour suppressor but only when 53BP1 is phosphorylated by ATM after DNA damage although the mechanism(s) and significance of the interaction of these two proteins are unclear. Here, we pinpoint a single ATM-phosphorylated residue in 53BP1—Ser25—that is required for binding of 53BP1 to hPTIP. Binding of phospho-Ser25 to hPTIP in vitro and in vivo requires two closely apposed pairs of BRCT domains at the C-terminus of hPTIP and neither pair alone can bind to phospho-Ser25, even though one of these BRCT pairs in isolation can bind to other ATM-phosphorylated epitopes. Mutations in 53BP1 and in hPTIP that prevent the interaction of the two proteins, render cells hypersensitive to DNA damage and weaken ATM signalling. The C-terminal BRCT domains of hPTIP are also required for stable retention of hPTIP at sites of DNA damage but this appears to be independent of binding to 53BP1. Thus, the BRCT domains of hPTIP play important roles in the cellular response to DNA damage.

Vaccinia-related Kinase 1 (VRK1) Is an Upstream Nucleosomal Kinase Required for the Assembly of 53BP1 Foci in Response to Ionizing Radiation-induced DNA Damage

“…This phosphorylation does not affect DNA repair (61), but it is necessary for 53BP1 binding to the BRCT domains of hPTIP (62,63), and its abrogation results in reduced CHK2 activation (63). This is consistent with the effect of VRK1 loss on CHK2 activation (Fig.…”

A tumor suppressive coactivator complex of p53 containing ASC-2 and histone H3-lysine-4 methyltransferase MLL3 or its paralogue MLL4

“…First, in an interesting study carried out in mouse models (31), haploid inactivation of ASC-2 was found to accelerate polyoma middle-T antigen-induced mammary tumorigenesis. Second, PTIP, which has been proposed to play important roles in cellular responses to DNA damage (32,33), recently was identified as an additional component of ASCOM (9,10). In this regard, it is important to note that the tumor suppressor p53 plays a key role in countering the adverse effects of DNA damage (23), which otherwise can be lethal or lead to oncogenic transformation, and that DNA damage induces the transcriptional activity of p53 via damage sensors such as ATM (23).…”

PTIP Regulates 53BP1 and SMC1 at the DNA Damage Sites

“…One includes the histone H3K4 methyltransferase ALR and its associated cofactors, the other contains DNA damage response proteins, including 53BP1 and SMC1 (30,31). Further experiments have revealed that DNA damage enhances the interaction between PTIP and 53BP1 (18,31).…”