Regulation of the DNA damage response by E2F4 phosphorylation in its T249/T251 conserved motif and Alzheimer’s disease.

Alzheimer's disease (AD) has a multifactorial etiology that includes DNA damage in neurons. The transcription factor E2F4, which can potentially regulate DNA repair, has two conserved threonines (T249/T251 in the mouse) that can be phosphorylated by p38MAPK (p38). The expression in vivo of the T249A/T251A E2F4 mutant form (E2F4DN) has been shown to be a multifactorial therapeutic agent against AD. In this work, we have analyzed the effects of E2F4 phosphorylation in T249/T251 on the DNA repair response (DDR). To this aim, we used N2a mouse neuroblastoma cells treated with 10 µM camptothecin (CPT), a treatment known to induce Cited2 expression and subsequent cell death. In this paradigm, the repression of Cited2 by E2F4 is abolished upon CPT treatment, thus allowing its E2F1-dependent expression followed by cell death. While E2F4 can be detected in both the nucleus and cytoplasm of N2a cells, phosphoT249-E2F4-specific immunoreactivity is specifically observed in the nucleus 4 h after treatment with CPT. Therefore, the known activation of p38 in response to CPT could lead to T249 phosphorylation of E2F4, thus suppressing its inhibition on E2F1 activity and allowing Cited2 expression. This hypothesis, is being tested in CPT- treated N2a cells co-transduced with adenoviral vectors expressing E2F1 together with either wild-type E2F4 or E2F4DN, in either the presence or absence of p38 inhibitors. In summary, our work provides support for a novel mechanism used by E2F4 to regulate the response to DNA damage in pathological situations, which could participate in the therapeutic capacity of E2F4DN against AD.