DNA repair deficiency in lymphocytes from patients with actinic keratosis

Abo-Darub, J. M (1977) DNA repair deficiency in lymphocytes from patients with actinic keratosis. PhD thesis, University of Glasgow.

Abstract

1. The literature covering the relevant aspects of the photochemistry of nucleic acids and the biological effects of ultra violet light radiation on cells is reviewed. The DM repair processes which have been shown to occur in micro-organisms and mammalian cells are discussed. The sun-sensitive conditions, xeroderma pigmentosum and actinic keratosis are described and compared. The defective DM repair synthesis in cells from patients with xeroderma pigmentosum and the possible role of DM repair defects in carcinogenesis are discussed. Human peripheral blood lymphocytes were isolated and used, in preference to skin fibroblasts, to study ultra violet light-induced DNA repair in patients different sun-sensitive conditions. The choice of lymphocytes for the study of DM repair is explained. Conditions for the study of ultra violet light-induced DM repair in human lymphocytes by two different methods, were established. One method used autoradiogaphic analysis to follow ultra violet light-induced DM repair synthesis in the non S-phase cells. The other measured the ultra violet light-induced incorporation of [3H] - thymidine into DM of lymphocyte cultures in the presence of hydroxyurea, which blocks DM replication in the small but significant fraction of dividing cells in the lymphocyte cultures. 4. Results obtained by these two methods show that the rate of ultra violet light-induced DKA repair in lymphocytes derived from actinic keratosis patients is only 50% of that in lymphocytes from age-matched normal individuals after 4 hours (by which time the repair of DBA in normal lymphocytes is complete). 5. Actinic keratosis is a condition of elderly people (aged 50 years or over), so the effect of subject age on DM repair was studied. It was shown that the rate of ultra violet light-induced DM repair in normal subjects does not vary significantly in the age range 17- 77 years. 6. The time course experiments indicated that, while the ultra violet light-induced MA repair in normal lymphocytes is complete after 4 hours, that in actinic keratosis lymphocytes is not. Subsequently, it was shown that, given twice the time (8 hours), lymphocytes derived from actinic keratosis patients complete the same amount of repair as that furnished by lymphocytes derived from normal subjects. 7. It was shown that DNA synthesis, in the presence of hydroxyurea, following ultra violet light-irradiation of human lymphocyte cultures, is mostly due to DNA repair synthesis and not to some form of ultra violet light-induced DM replication. 8. It was shown that the observed difference between DKA repair, measured by the incorporation of [3H] - thymidine in lymphocytes from actinic keratosis patients and normal subjects is not due to differences in [3H] - thymidine uptake or to different thymidine nucleotide pool sizes. 9. A novel method was developed to study DM repair in lymphocytes, based on following the recovery of phytohaemagglutinin-stimulated DMA replication after inhibition by ultra violet light. This method, unlike those previously used to assess DWA repair, measures the extent of successful repair (in that it allows the continuation of DMA replication)o The results obtained by this method confirmed that ultra violet light-induced DM repair in lymphocytes derived from actinic keratosis patients is about 50% that of lymphocytes derived from age-matched normal individuals. 10. Preliminary experiments have shown that lymphocytes derived from patients with lupus erythematosus also have a reduced rate of ultra violet light-induced DM repair, but that lymphocytes derived from patients with either melanoma or basal cell carcinoma have normal levels of repair. 11. The conclusions which have emerged from this study regarding the defective DNA repair in lymphocytes from patients with actinic keratosis are discussed. The possibility that defective DNA repair is a common basis for both actinic keratosis and xeroderma pigmentosum is considered. The unlikely contribution of photoreactivation and post-replication repair mechanisms to the DM repair measured in this work is discussed. The reasons in favour of actinic keratosis being genetically determined are considered.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Advisers: R MS Smellie; J D Pitts
• Keywords: Biochemistry
• Date of Award: 1977
• Depositing User: Enlighten Team
• Unique ID: glathesis:1977-72273
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 May 2019 15:12
• Last Modified: 24 May 2019 15:12
• URI: https://theses.gla.ac.uk/id/eprint/72273