HISTIDINE AVAILABILITY ALTERS GLUCAGON GENE-EXPRESSION IN MURINE ALPHA-TC6 CELLS

Because individual amino acids (AA) stimulate glucagon release from pa ncreatic alpha-cells, the purpose of this study was to determine if in dividual AA could influence glucagon gene expression. Preproglucagon m RNA levels were 67% lower (P < 0.05) in mouse alpha TC6 cells incubate d for 12 h in amino acid-free medium compared with cells incubated in complete medium containing all 20 AA. A time-course study indicated th at alpha TC6 cells incubated in amino acid-free medium +/- 1 mu mol/L puromycin or amino acid-containing medium plus puromycin exhibited sim ilar preproglucagon mRNA decreases over 12 h. When 1 mu mol/L actinomy cin was added to medium with or without AA, ppG mRNA concentrations de creased (P < 0.05) for 3 h; however, values at 12 h were not different than those at 3 h. Deletions of single AA from complete medium demons trated that only histidine removal or depletion reproduced the decreas e in ppG mRNA observed in amino acid-free medium. We conclude that his tidine is involved in the regulation of preproglucagon mRNA levels in alpha TC6 cells and that this regulation may be operative during both transcriptional and post-transcriptional events.