Suk-Hee Lee - US grants

DESCRIPTION: (adapted from the proposal): The proposal suggests that RPA, a multisubunit (p70, p34 and p11) protein, which is involved in DNA replication and DNA repair, may be a target for regulation. This stems from the fact that the amount of RPA subunits does not vary during the cell cycle. Hence, the DNA replication and DNA repair activities of RPA could be regulated by either protein assembly or post- translational modification. The investigator proposes to test whether the assembly of the RPA complex is regulated during the cell cycle. In addition, he will examine whether RPA regulates the formation of initiation complexes at the SV40 origin of replication. Since phosphorylation of RPA could have a role in regulating its activities, the investigator will map the phosphorylation sites and will characterize the kinases in this phosphorylation. RPA phosphorylation sites will be mutated and mutant RPA will be analyzed along with the wild type RPA in a coupled repair- replication system, which was recently developed in the investigator's laboratory.

Cisplatin is widely used anti-cancer chemotherapeutic drug that induces DNA damage by forming Cisplatin-DNA abducts in cells. In vivo and in citron studies strongly suggest that most of the Cisplatin-DNA abducts are repaired through nucleotide excision repair (NER) pathway. Due to extensive efforts, we now have significant knowledge about the mechanism of NER and the proteins involved. Recognition of DNA damage is a critical step in the early stage of repair. Xeroderma pigmentosum group A complementing protein (XPA), replication protein A (RPA), XPC-hHR23B, and XPE can independently bind damaged DNA. However, it is still in debate how the damaged recognition proteins function at the damaged DNA site. In this proposal, we will use biochemical and molecular approaches to address the following specific questions: 1) how multiple damage recognition factors function at the damaged DNA site? 2) do zinc-finger proteins (RPA and XPA) cause structural distortion at the damaged site? If so, is it necessary for dual incisions? 3) how do the damaged recognition factors affect the efficiency and accuracy of 3' and 5'- incisions? In the first aim, binding kinetics of individual damage recognition proteins to damaged DNA, interactions between damaged recognition factors, and assembly of a preincision complex will be analyzed using purified repair proteins (RPA,XPA,XPC-hHR23B, and TFIIH) and Cisplatin-induced intra strand crossed-linked DNA. In the second aim, we will analyze the molecular basis for structural dissertation of Cisplatin-damaged DNA. Conformational charges of damage recognition proteins following their interment with amazed DNA and the role of the zinc-finger motif of RPA and XPA in this event will be analyzed. We will use a foot printing assay to analyze the structural distortion of damaged DNA induced by damage recognition factors. In addition, fluorescence resonance energy transfer (FRET) method will be utilized to simultaneously monitor both the conformational change of damage recognition proteins and distortion of the damaged DNA. In the third aim, we will attempt to functionally define the role of damage recognition factors in 3' and 5' incision activity by XPG and ERCCI-XPF will be examined. Both the accuracy and efficiency of the 3' and 5' incisions will be analyzed in advance with the kinetics of incision activity. Various mutants of damage recognition factors (RPA and XPC) will be used to examine any unique role these proteins possess in 3' and 5' incising.

DESCRIPTION (provided by applicant): The human genome is littered with sequences derived from transposable elements from the Hsmar1 transposon, but there is only one intact copy of the Hsmar1 transposase gene termed Metnase (also known as SETMAR) that exists within a chimeric SET-transposase fusion protein. Although Metnase retains most of the transposase activities, it has evolved as a double-strand break (DSB) repair protein in anthropoid primates. Metnase is localized on chromosome 3p26, a region of frequent abnormalities in various cancers and is highly expressed in most tissues and cell lines. Mutations in Metnase that cause early termination were found in many transformed cell lines, although clinical relevance of these mutations has not been established. Our long-term goal is to understand how a protein with transposase activity in humans promotes DSB repair and chromosome decatenation, and what role the SET domain may play. Given that Metnase requires both the SET and transposase domains for its function(s) in DSB repair, we hypothesize that the acquisition of new functions may have resulted from a chimeric fusion between transposase and the SET domains. In this study we proposed three specific aims to elucidate the mechanism of this human SET- transposase protein in DSB repair and chromosome decatenation. Aim 1: Determine the mechanism by which Metnase is localized to DSB sites. We will identify the region within the SET domain of Metnase crucial for localization to DSB sites following IR treatment. We will also investigate whether the interaction of Metnase with Pso4, a Metnase binding partner that plays a crucial role in Metnase localization at DSB sites, is crucial for Metnase localization at DSB sites. Finally, we will examine whether Metnase directly interacts with the Ku70/80 complex. If so, a mutant Metnase defective in interaction with Ku complex will be generated, and we will determine how this mutant differs from wt-Metnase in their localization at DSB sites. Aim 2: Determine the role(s) of Metnase's biochemical activities in DNA end joining and chromosome decatenation. Metnase not only possesses a structure-specific endonuclease and HLMT activities, but also interacts with Lig4, Pso4, and Topo II1, all of which could play role(s) in NHEJ repair and/or chromosome decatenation. We will examine how Metnse's biochemical activities are involved in DNA end joining and chromosome decatenation. First, we will substitute key amino acids within the catalytic site identified from the crystal structure of Metnase transposase domain and examine the mutants for DNA cleavage, DNA end processing, and end joining activities. Secondly, we will examine how Metnase's interaction with Lig4 affects recruitment of Lig4-XRCC4 to DSB sites and DNA end joining. Thirdly, we will examine how Metnase binding partner (Pso4) and its interaction with Metnase influence DNA end joining. Fourth, we will examine whether Metnase mutant(s) lacking HLMT and/or auto-methylation activity support stimulation of DSB repair. Finally, Metnase mutants lacking its biochemical activities will be examined for promotion of chromosome decatenation activity.