Functional capacity of XRCC1 protein variants identified in DNA repair-deficient Chinese hamster ovary cell lines and the human population.

XRCC1 operates as a scaffold protein in base excision repair, a pathway that copes with base and sugar damage in DNA. Studies using recombinant XRCC1 proteins revealed that: a C389Y substitution, responsible for the repair defects of the EM-C11 CHO cell line, caused protein instability; a V86R mutation abolished the interaction with POLbeta, but did not disrupt the interactions with PARP-1, LIG3alpha and PCNA; and an E98K substitution, identified in EM-C12, reduced protein integrity, marginally destabilized the POLbeta interaction, and slightly enhanced DNA binding. Two rare (P161L and Y576S) and two frequent (R194W and R399Q) amino acid population variants had little or no effect on XRCC1 protein stability or the interactions with POLbeta, PARP-1, LIG3alpha, PCNA or DNA. One common population variant (R280H) had no pronounced effect on the interactions with POLbeta, PARP-1, LIG3alpha and PCNA, but did reduce DNA-binding ability. When expressed in HeLa cells, the XRCC1 variants-excluding E98K, which was largely nucleolar, and C389Y, which exhibited reduced expression-exhibited normal nuclear distribution. Most of the protein variants, including the V86R POLbeta-interaction mutant, displayed normal relocalization kinetics to/from sites of laser-induced DNA damage: except for E98K and C389Y, and the polymorphic variant R280H, which exhibited a slightly shorter retention time at DNA breaks.

Leukemia Blast Crisis: A Simulation Case for Residents.

INTRODUCTION: Oncologic emergencies are life-threatening and often require advanced team-management skills as well as a mastery of disease processes and therapeutic interventions. Simulation of an oncologic emergency case is a useful way to experience, reflect on, and practice these skills. This case involving a simulated patient in blast crisis was created as part of our Emergency Medicine (EM) Resident Simulation Curriculum at the Perelman School of Medicine at the University of Pennsylvania. METHODS: This case is based on an actual patient seen in our emergency department and highlights specific teaching points and potential pitfalls in treatment algorithms. It details a 40-year-old female with history of acute myeloid leukemia presenting with fatigue for 2 days, tachycardia, and labored breathing. The patient develops worsening respiratory distress if not intervened upon and progresses to pulseless electrical activity arrest. Lab work is notable for markedly elevated white blood cell count and acidosis. A SimMan or SimMan3G is required for the simulation. The associated debriefing materials are Included in this educational resource. Evaluation of learner performance is mapped to the EM Milestones. RESULTS: Eighteen of the 20 (90%) EM residents that participated in this simulation, responded to the Likert-scale postsession survey. Of those who responded, 83% agreed or strongly agreed that the case was realistic and 89% agreed or strongly agreed that the case was useful. DISCUSSION: The simulation venue offers a unique opportunity to address team dynamics as well as provide a forum for didactic learning as it is often difficult to debrief a critical case while working in real-time patient care settings.