SUPPRESSION OF TRANSCRIPTION FACTOR PDX-1 IPF1/STF-1/IDX-1 CAUSES NO DECREASE IN INSULIN MESSENGER-RNA IN MIN6 CELLS/

The insulin gene transcription factor PDX-1/IPF1/STF-1/IDX-1 plays a k ey role in directing beta cell-specific gene expressions, Recently, im pairment of PDX-1 expression or activity has been observed in beta cel l-derived HIT cells cultured under high glucose concentrations, and th is has been suggested as a possible cause of the decrease in insulin g ene transcription, To investigate the pathophysiological significance of PDX-1 as a determinant of the rate of insulin gene transcription, w e suppressed its expression in beta cell-derived MIN6 cells using an a ntisense oligodeoxynucleotide (ODN) and searched for possible changes in the beta cell-specific gene expression, Treatment of MIN6 cells wit h an 18-mer phosphorothioate ODN complementary to a sequence starting at the translation initiation codon of PDX-1 caused a potent, concentr ation-dependent reduction in PDX-1 expression; addition of 2 mu M anti sense ODN could reduce PDX-1 expression to 14+/-4% of the control. The re was also a decrease in its DNA binding to the insulin gene A elemen t, Despite such suppression of PDX-1, Northern blot analysis revealed no decrease in the amount of insulin mRNA in the MIN6 cells. Similarly , no changes were detected in the transcription of the glucokinase or islet amyloid polypeptide gene, for which PDX-1 was shown to function as a transcription factor, Thus, our findings dispute the physiologica l significance of PDX-1 in determining the rate of insulin gene transc ription. This means that other components constituting the transcripti on-controlling machinery need to be evaluated in order to understand t he molecular basis of impaired insulin biosynthesis such as that obser ved due to glucose toxicity.