In vitro effect of 3,5,3'-triiodothyronine on poly(ADP-ribosyl)ation of DNA topoisomerase I.
DNA topoisomerase I activity (topo I) is known to be inhibited by poly(ADP-ribosyl)ation. Both poly(ADP-ribose)polymerase (pADPRP) and DNA topoisomerase I participate to major biological events, such as DNA transcription, repair and synthesis. It has been shown that thyroid hormones, such as 3,5,3'-triiodothyronine (T3), stimulate DNA transcription and down-regulate pADPRP activity. Using an in vitro model, we have studied the poly(ADP-ribosyl)ation of topo I, in vitro, in the presence of T3. T3 treatment of pADPRP inhibits the enzyme up to 75-80% of control activity. DNA topoisomerase I relaxing activity was determined on supercoiled plasmid DNA, and topoisomers were separated by agarose gel electrophoresis. Poly(ADP-ribosyl)ation completely inhibits the relaxing activity of topo I, with respect to non-ribosylated controls, but the activity remains unaffected when pADPRP is inactivated by heat or treated with specific inhibitors, such as 3-aminobenzamide (3ABA). In this study we show that treatment of pADPRP with T3 reduces the inhibition on topo I. In this system 10(-8) M T3 was effective in maintaining almost all topo I activity, even though modifications in processivity and distributivity of the reaction were noted. These data support a close relationship between pADPRP and topo I in hormone-stimulated DNA transcription.
Giannoni
P
P
Istituto di Fisiologia Generale, Università di Genova.
Scarabelli
L
L
Orunesu
M
M
Cesarone
C F
CF
D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000187:drug effects*; D011065:Poly(ADP-ribose) Polymerases / Q000737:chemistry / Q000187:drug effects*; D014284:Triiodothyronine / Q000494:pharmacology*
D014284:Triiodothyronine; D011065:Poly(ADP-ribose) Polymerases; D004264:DNA Topoisomerases, Type I