Absence of stimulation of poly(ADPmribose) polymerase activity in patients predisposed to colon cancer L Crist6vdo1, MC Lechner2, P Fidalgo3, CN Leitao3, FC Mira3 and J Rueff1 'Department of Genetics, Faculty of Medical Sciences, New University of Lisbon, Rua da Junqueira, 96, P-1300 Lisbon, Portugal; 2Gulbenkian Institute of Sciences, Laboratory of Biochemistry, Oeiras, Rua da Quinta Grande, Apartado 14, P-2781 Oeiras, Portugal; 3Portuguese Institute of Oncology, Service of Gastroenterology, Rua Prof. Lima Basto P-1070 Lisbon, Portugal Summary Poly(ADP-ribose)polymerase (PARP) has been implicated in DNA repair mechanisms and the associated activity shown to markedly increase after DNA damage in carcinogen-treated cells. A defective DNA repair has been associated to the aetiology of human cancers. In order to assess the potential role of this enzyme in cellular response to DNA damage by y-radiation, we studied the activity of PARP in patients with familial adenomatous polyposis (FAP). We compared poly(ADP-ribose)polymerase activity by the rate of incorporation of radioactivity from [3H]adenine-NAD+ into acid-insoluble material in permeabilized leucocytes from FAP patients and healthy volunteers. Concomitantly, the intracellular levels of NAD+ -the substrate for the PARP -and the reduced counterpart NADH were determined using an enzymatic cycling assay 30 min after [60Co] y-ray cells irradiation. Our results demonstrate that a marked stimulation of PARP activity is produced upon radiation of the cells from healthy subjects but not in the FAP leucocytes, which concomitantly show a marked decrease in total NAD+/NADH content. Our observations point to a role of PARP in the repair of the y-radiation-induced DNA lesions through a mechanism that is impaired in the cells from FAP patients genetically predisposed to colon cancer. The differences observed in PARP activation by yradiation in patients and healthy individuals could reflect the importance of PARP activity dependent on treatment with y-rays. The absence of this response in FAP patients would seem to suggest a possible defect in the role of PARP in radiation-induced DNA repair in this cancerprone disease.Keywords: poly(ADP-ribose)polymerase; familial adenomatous polyposis; radiation; DNA repair Poly(ADP-ribose)polymerase (PARP, EC 2.4.2.30) is a chromatinassociated enzyme that catalyses the transfer of the ADP-ribosyl moiety from NAD+ into various acceptor proteins (Chambon et al, 1966;Nishizuka et al, 1968). Among these are nucleosomal core histones, histone HI, HMG proteins, topoisomerases I and II and PARP itself (Braz and Lechner, 1986; Althaus, 1987). The catalytic activity of PARP is strongly dependent on the presence of DNA strand breaks, which represent the sites for the enzyme recognition (Gradwohl et al, 1990;Ikejima et al, 1990;Molinete et al, 1993;Burkle et al, 1994;Panzeter et al, 1994). The stimulation of PARP by reactive oxygen species has been demonstrated Heller et al, 1995;Crist6vao and Rueff, 1996).The precise role of PARP in DNA repair ...