Co-regulation and function of Pur-gamma and WRN in the CNS

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PROJECT SUMMARY/ABSTRACT This project will elucidate the mechanisms by which functions of two proteins, known to be important for CNS development and prevention of genomic instability, respectively, are coordinated through shared gene regulation and cooperative protein activity. Mutations in the WRN gene lead to the progeroid disorder Werner syndrome, which is characterized by genomic instability and early senescence. Neurodegeneration is a feature of Werner syndrome. Our overall hypothesis is that the PURG gene encoding Pur-gamma (Purg), a little studied member of the Pur protein family, is coordinantly regulated at specific times with the WRN gene and that the two encoded proteins function cooperatively. PURG and WRN are located head-to head and are separated by a shared control sequence of 92 bp. The two proteins carry out distinct aspects of DNA strand separation and processive unwinding. Purg is expressed in both glial cells and neurons, and it is present at high levels in early brain development, as is WRN. Purg has previously been shown to have two isoforms, and we have found both isoforms to be present in the nucleus and nucleolus of oligodendroglioma cells. Pur proteins are involved in local DNA strand separation, and they bind to G-rich sequences called PUR elements. The WRN protein also has a preference for G-rich sequences and is a processive helicase that unwinds DNA with cofactors that inhibit or enhance its activity. We hypothesize that PURG and WRN genes are coregulated to allow coordinate function of Purg in known WRN functions, including DNA repair and telomere homeostasis, in cells of the CNS. Our rationale for this project is that 1) WRN and Purg proteins interact and colocalize with each other in neural cells; 2) WRN and Purg have closely related and potentially complementary functions both advantageous for DNA repair; and 3) the WRN and PURG gene promoters share regulatory elements. This project has two specific aims. The first will determine how the PURG and WRN genes are coordinately regulated in glial cells via sequence elements in a shared central control region. The second will determine the manner in which the Purg and WRN proteins function cooperatively in DNA repair in primary neural cells. Insights from these data will be of significance not only for the elucidation of the cellular pathways in which these two proteins function, but also for enhancing our understanding of a process commonly disrupted in neurodegenerative diseases.