Swift transduction of DNA double-strand break (DSB) signals is key to effective DNA repair and maintenance of genome stability. Indeed, genetic mutations that perturb the DSB response circuitry compromises genome integrity, and are causally linked to a cohort of human diseases, including cancer and developmental deficits.

As part of our effort in defining the mammalian DNA Damage Response (DDR) network, we recently set out to elucidate how nuclear actin dynamics supports DSB metabolism, and have uncovered the actin regulator Spir1 as an early respondent to DSBs. We found that Spir1 accumulates at laser-induced DNA damage tracks, and that this is effected via its putative phosphoinositide-interacting FYVE domain, suggesting that Spir1 may target the damaged chromatin by tethering to phosphoinositides. In line with the idea that phosphoinositide species may decorate the DSB microenvironment to drive DDRs, we further showed that laser microirradiation led to accrual of phosphatidylinositol biphosphate (PIP2) reporters, highlighting potential early roles of PIP2 in chromatin responses to DSBs.

To systematically dissect how PIP2s may serve as signaling intermediates on the DSB-flanking chromatin, we will first establish how the Spir1 FYVE is targeted to the damaged chromatin, and will examine its interaction with PIP2 in vitro and in vivo. We will define the genetic regulation of nuclear PIP2 metabolism, and will delineate how PIP2s contribute to DSB signal transduction and repair processes. Moreover, we will profile the PIP2 interactome to isolate novel DSB response factors, and will systematically determine how PIP2 metabolism impacts genome stability and cell responses to genotoxic stress.

Given the emerging roles of PIP2s in actin dynamics, we propose that PIP2s may underlie early DSB responses and are important secondary messengers in genome integrity protection. Our proposed work thus represents a timely and exciting initiative to reveal how nuclear PIP2s mediate DSB responses, and how genetic perturbation of PIP2 metabolic pathways contributes to genome instability and human tumorigenesis.