Cholera toxin affects nuclear ADP-ribosylation in GH1 cells

Area of Science:

• Cellular Biology
• Biochemistry
• Molecular Biology

Background:

• Poly(ADP-ribosyl)ation is a crucial post-translational modification involved in DNA repair and gene regulation.
• Cholera toxin is known to modulate cellular signaling pathways, particularly those involving cyclic AMP.

Purpose of the Study:

• To investigate the effect of cholera toxin on poly(ADP-ribosyl)ation in GH1 cells.
• To determine the impact of cholera toxin on NAD+ levels and protein modification.
• To explore the role of cyclic AMP in mediating cholera toxin's effects on poly(ADP-ribosyl)ation.

Main Methods:

• GH1 cells were incubated with cholera toxin or dibutyryl cyclic AMP.
• [32P]ADP-ribose incorporation into histones and non-histone nuclear proteins was measured.
• Cellular NAD+ levels were quantified.
• Poly(ADP-ribosyl)ated components were analyzed after micrococcal nuclease digestion.

Main Results:

• Cholera toxin inhibited [32P]ADP-ribose incorporation into nuclear proteins by over 50% after 24 h.
• A generalized decrease in poly(ADP-ribosyl)ation was observed across all protein acceptors and chromatin components.
• Cellular NAD+ levels decreased by 40-80% following cholera toxin treatment.
• An initial increase in incorporation occurred after 3 h, preceding the inhibition.
• Dibutyryl cyclic AMP also inhibited nuclear poly(ADP-ribosyl)ation.

Conclusions:

• Cholera toxin significantly inhibits nuclear poly(ADP-ribosyl)ation in GH1 cells.
• The observed inhibition is associated with a reduction in cellular NAD+ levels.
• Cyclic AMP likely mediates the inhibitory effects of cholera toxin on poly(ADP-ribosyl)ation.