DNA excision repair in permeable human fibroblasts

Area of Science:

• Molecular Biology
• Cell Biology
• DNA Repair Mechanisms

Background:

• Ultraviolet (UV) irradiation is a potent DNA-damaging agent that induces various lesions, primarily pyrimidine dimers.
• Human fibroblasts possess intricate DNA repair pathways to counteract UV-induced damage.
• Understanding the kinetics and molecular events of DNA repair in permeabilized cells is crucial for mechanistic studies.

Purpose of the Study:

• To characterize the DNA repair processes activated in permeabilized human fibroblasts following UV irradiation.
• To investigate the efficiency of gap-filling and ligation during DNA repair in vitro.
• To assess the reassembly of chromatin structure at repair sites.

Main Methods:

• Confluent human fibroblasts were exposed to UV irradiation and subsequently permeabilized.
• Reparative DNA synthesis was measured using radiolabeled precursors.
• DNA strand sizes and repair patch characteristics were analyzed using nucleases (micrococcal nuclease, exonuclease III, nuclease S1).

Main Results:

• A 20-minute incubation period was optimal for maximum reparative DNA synthesis in permeabilized cells.
• Permeabilized cells demonstrated efficient gap-filling and ligation of repair patches, with ~85% of synthesized DNA resisting nuclease digestion.
• Impaired reassembly of nucleosome structure at repair sites was observed, indicated by increased sensitivity to micrococcal nuclease and minimal changes during a chase period.

Conclusions:

• UV-activated DNA synthesis in permeabilized fibroblasts represents the continuation of excision repair initiated in intact cells.
• Gap-filling and ligation are efficient in permeabilized cells, but the activation of repair synthesis and chromatin reassembly are compromised.
• The study highlights distinct efficiencies in different stages of the DNA repair process within permeabilized cell systems.