NUDT2 Disruption Elevates Diadenosine Tetraphosphate (Ap(4)A) and Down-Regulates Immune Response and Cancer Promotion Genes

Marriott, Andrew S.; Vasieva, Olga; Fang, Yongxiang; Copeland, Nikki A.; McLennan, Alexander G.; Jones, Nigel J.

Finally, loss of NUDT2 could have consequences through the loss of interaction with any binding partner. NUDT2 may have a significant nuclear location [155, 156] and has been documented to bind to the replicative helicase component MCM6 [157] . While this may in some way be related to the inhibition of replication initiation by Ap 4 A [17] , it is not clear how loss of this interaction would have the profound effect on transcription observed in NuKO cells. NUDT2 has also been reported to bind to unliganded estrogen receptor beta (ESR2) in the cytosol [158] . This is interesting given the reported repression of NUDT2 expression by estradiol [78, 159] . However, no significant expression of ESR2 was detected in KBM-7 cells (S2 Table and [38] ) and so it seems unlikely that the effects of NUDT2 disruption involve ESR2mediated gene expression. Thus, aside from a theoretical effect of NUDT2 loss on mRNA decapping, it seems reasonable to conclude that most of the transcriptional effects reported here are caused by an increased level of its major substrate, Ap 4 A. We did attempt to answer this question directly by expression of the Escherichia coli ApaH gene in NuKO cells. ApaH encodes a symmetrically-cleaving Ap 4 A hydrolase that it structurally unrelated to NUDT2 [160] and in so doing we hoped to reduce Ap 4 A to normal levels in a NUDT2-negative background. However, ApaH expression proved to be toxic to the cells, possibly because ApaH may also have protein phosphatase activity [161] .