THE HUMAN GLUCOKINASE GENE BETA-CELL-TYPE PROMOTER - AN ESSENTIAL ROLE OF INSULIN PROMOTER FACTOR 1 PDX-1 IN ITS ACTIVATION IN HIT-T15 CELLS/

The glycolytic enzyme glucokinase plays a primary role in the glucose- responsive secretion of insulin, and defects of this enzyme can cause NIDDM, As a step toward understanding the molecular basis of glucokina se (GK) gene regulation, we assessed the structure and regulation of h e human GR gene beta-cell-tgpe promoter The results of reporter gene a nalyses using HIT-T15 cells revealed that the gene promoter was compri sed of multiple cis-acting elements, including two primarily important cis-motifs: a palindrome structure, hPal-1, and the insulin gene cis- motif A element-like hUPE3, While both elements were bound specificall y by nuclear proteins, it was the homeodomain-containing transcription factor insulin promoter factor 1 (IPF1)/STF-1/PDX-1 that bound to the hUPE3 site: IPF1, when expressed in CHO-K1 cells, became bound to the hUPE3 site and activated transcription. An andi-IPF1 antiserum used i n gel-mobility shift analysis supershifted the DNA protein complex for med with the hUPE3 probe and nuclear extracts from HIT-T15 cells, thus supporting the involvement of IPF1 in GK gene activation in HIT-T15 c ells. In contrast to the insulin gene, however, neither the synergisti c effect of the Pan1 expression on the IPF1-induced promoter activatio n nor the glucose responsiveness of the activity was observed for the GK gene promoter. These results revealed some conservative but unique features for the transcriptional regulation of the beta-cell-specific genes in humans, Being implicated in insulin and GK gene regulations a s a common transcription factor, IPF1/STF-1/PDX-1 is likely to play an essential role in maintaining normal beta-cell functions.