Investigation of HJURP action (Holliday Junction Recognizing Protein) in DNA repair activity of glioblastoma cells

Abstract

Astrocytomas comprise the most common type of primary brain tumors in adults. They are classified in diffuse astrocytoma (grade II), anaplastic astrocytoma (grade III) and glioblastoma (grade IV). Among them, glioblastoma (GBM) is the most frequent and aggressive type, and the majority of patients survive approximately only one year after diagnosis, due to invasiveness and high resistance of tumor cells to radio and chemotherapy. Recent studies revealed that molecular characterization is fundamental for more accurate diagnoses and development of effective therapies. Within this context, we have previously found that HJURP (Holliday Junction Recognizing Protein) is highly overexpressed in GBMs, strongly correlated with patient survival, and essential for survival of GBM cell lines but not for astrocytes and non-tumor fibroblasts. HJURP was primarily associated with DSBs repair by Kato et al. (2007) who described increased expression of HJURP after genotoxic stress and its interaction with proteins of the MRN complex, which is active in the recognition of DNA lesions. However, additional reports to support this function are still required. HJURP also acts as the chaperone of the centromeric variant of histone H3 (CENP-A), performing its loading in chromatin. This activity is well established and quite characterized, regarding mechanisms, protein domains involved and the regulation in cell cycle. Preliminary data of our group, in collaboration with Dr. Brendan D. Price (Dana-Farber Cancer Institute - Harvard University), revealed the recruitment of HJURP to sites of DNA double-strand breaks in the beginning of cellular response to damage. Thus, we intend to elucidate the mechanisms of HJURP function in DNA repair and resistance of GBM cells to ionizing radiation, in an innovator study on the subject. For this, we propose: i) to confirm the HJURP requirement for the DNA repair activity, ii) investigate the participation of HJURP in the repair pathways through homologous recombination and/or non-homologous end joining, iii) dissect in which step of DNA repair HJURP acts, iv) evaluate the impact of reducing HJURP levels on repair efficiency after treatment with ionizing radiation, v) investigate whether the presence of HJURP at injury sites is involved with chromatin remodeling. (AU)