We modeled ATM sequence variants identified in UK A-T patients to determine the stability and kinase activity of the resulting proteins as well as the distribution of these mutations across the coding region.
The isoflavonoids genistein and quercetin activate different stress signaling pathways as shown by analysis of site-specific phosphorylation of ATM, p53 and histone H2AX.
While in controls both subpathways may be mediated by ATM kinase, in ataxia telangiectasia cells caffeine-sensitive ATR kinase and the caffeine-insensitive DNA-PK kinases might be responsible for DNA repair and the G(2) delay subpathways, respectively.
In contrast, in AT cells in which ATM is absent or mutated activation of P53 and its target genes is abrogated, allowing cells to replicate with damage in the presence of As, with cell death ensuing by a pathway different from P53.
These data suggest that although ATM-specific mRNA is abundant in A-T cells, the abnormal ATM protein is unstable and is quickly targeted for degradation.
We quantified ATM protein expression in four of the families and found variable ATM protein expression (0-6.4%), further evidence for mutant ATM protein expression in both classic and variant A-T patients.
Ataxia-telangiectasia in the Japanese population: identification of R1917X, W2491R, R2909G, IVS33+2T-->A, and 7883del5, the latter two being relatively common mutations.
In our study, we have determined the ATM mutation spectrum in 19 classical A-T patients, including some immigrant populations, as well as 12 of Dutch ethnic origin.
We also show that 25% of all A-T patients carried in-frame deletions or missense mutations, many of which were also associated with expression of mutant ATM protein.