Unexpected roles of phosphoinositides in the nucleus

PROJECT SUMMARY / ABSTRACT Phosphoinositides (PIs) are a minor class of phospholipids often comprising less than 1% of the cellular lipid cohort. Despite the low abundance, PIs have huge impacts on cell physiology and alterations of PI signaling pathways are associated with the pathogenesis of many human diseases including neurodegenerative diseases, metabolic disorders, autoimmunity, and cancer. This pathophysiological importance is largely due to the signaling roles of PIs which depend on the subcellular distribution of PIs and on key interactions between PIs and PI effectors. A twist in PI signaling is that in contrast to general belief, a substantial fraction of PIs is found in non-membranous nuclear compartments. The nature and functions of nuclear PIs remains largely unknown due to the lack of systematic studies of nuclear PIs and PI effectors. We have expertise in defining and characterizing novel PI effector proteins involved in key signaling pathways including vesicular trafficking, cytoskeleton dynamics, and transcription regulation. Since PI kinases are often associated with PI effectors thus ensuring PI generation is spatiotemporally linked to PI effector activation, we have performed proteomic analyses to identify the interactomes of the nuclear PI-generating kinases. Out of these proteomic screens, we have validated several nuclear complexes that associate with nuclear PI kinases or with PIs themselves. The validated complexes include transcription factors and coactivators, epigenetic enzymes and associated corepressors, the DNA repair machinery, and factors involved in RNA processing. We recently discovered that nuclear PIs accumulate at distinct subnuclear regions such as nuclear speckles and DNA double-strand breaks. Based on our novel discoveries of PIs and PI kinases interacting with effectors in the nucleus, the overarching goal of my research program is to decipher the signaling pathways emanating from the nuclear PIs. Our overall hypothesis is that upon suitable stimuli the activation of nuclear PI kinase at specific subnuclear compartments elevates the local concentration of nuclear PIs and these nuclear PI foci function as platforms to regulate PI effectors recruited to the foci mediating transcription regulation and assembly of complexes that regulate epigenetic changes. The goals of my research programs for the next five years include dissecting the nature and subnuclear distribution of nuclear PIs using novel microscopic tools which will enable us to obtain high resolution images of the nuclear PIs, defining the new roles of PIs regulating chromatin positioning to nuclear speckles, and investigating novel roles of nuclear PIs in regulating gene expression with focuses on transcription regulation and epigenetic repression with innovative cell biological, genome-wide, and biochemical approaches. Upon the completion of the research programs, we will obtain insight into the unexpected roles and molecular mechanism of PIs in the nucleus, with the goal of identifying novel strategies for targeting the nuclear PI signaling pathways dysregulated in diverse human disease.