Western blot analysis showed that UV light-induced DNA damage results in an electrophoretic mobility shift of cytoplasmic, but not nuclear, ATR — from what the authors designate the ATR-L form to the ATR-H form. This shift was not caused by post-translational modification but was instead shown to reflect a conformational change catalysed by the prolyl isomerase PIN1. In the absence of PIN1 catalytic activity, cytoplasmic ATR was predominantly of the ATR-H cis-conformation, even in the absence of UV irradiation. The results suggest that PIN1 maintains the ATR-L trans-conformation under normal conditions. This was confirmed in an in vitro isomerization assay, which further showed that phosphorylation of ATR-H is required for PIN1 binding, and that UV irradiation leads to the phosphorylation and inactivation of PIN1 and possibly to the dephosphorylation of ATR-H.
The combined effect of UV irradiation is therefore to prevent PIN1-mediated ATR-H to ATR-L isomerization. Following UV irradiation, the accumulated cytoplasmic ATR-H was localized exclusively to the mitochondrial outer membrane through direct interaction with the apoptotic protein BID. ATR contains three potential BH3-like domains, of which the second domain (amino acids 462–474) was required for ATR-H–BID interaction. The PIN1-induced isomerization of ATR-H to ATR-L results in a conformational change of the amino-terminal region of ATR that is thought to sequester this BH3-like domain and prevent binding to BID.
This is a preview of subscription content, access via your institution
