Thyroxine control of pancreatic amylase gene expression: modulation of PTF1 binding activity.

The role of pancreas specific transcription factor (PTF1) in thyroxine (T4) modulation of amylase gene expression in suckling rats was evaluated. Electrophoretic mobility shift assay (EMSA) was used to determine the PTF1 binding activity by the amount of a synthetic oligonucleotide containing the amylase enhancer sequence bound by nuclear protein extracts. Nuclear protein from rat pancreata showed a developmental increase of PTFI activity correlated with age. To study the action of T4, pups were made hyperthyroid by T4 injection and hypothyroid by feeding propylthiouracil (PTU) to the lactating dams. EMSA of nuclear proteins isolated from these groups showed an increase in PTF1 binding activity in the T4 group and a decrease in the PTU group. Concomitantly, T4 increased, while PTU decreased both amylase enzyme and mRNA concentrations. T4 replacement reversed the effect of PTU on PTF1 binding, amylase enzyme activity and mRNA levels. To examine the age dependence of T4 effects, T4 was injected to pups for 5 days prior to killing at the age of 15, and 25 days. T4 was effective when given at an earlier age (15 days) but not at a later stage (25 days) in increasing amylase activity and amylase mRNA levels. Nuclear proteins isolated from pancreata of these groups showed an increase in PTF1 binding activity in the T4-treated 15-day-olds but not in the 25-day-olds in comparison to their corresponding age matched littermates. These results suggest that PTF1 is an important intermediary in T4 modulation of amylase gene expression during ontogeny of the rat exocrine pancreas.