MULTIPLE TRANSCRIPTS ENCODED BY THE THYROID-SPECIFIC ENHANCER-BINDINGPROTEIN (T EBP) THYROID-SPECIFIC TRANSCRIPTION FACTOR-I (TTF-1) GENE - EVIDENCE OF AUTOREGULATION/

Multiple transcripts derived from the gene encoding rat thyroid-specif ic enhancer-binding protein (T/EBP)/thyroid-specific transcription fac tor-1 (TTIF-1) were identified by complementary DNA cloning and sequen cing, and Northern blotting analyses. Six different types of complemen tary DNAs were identified that differ at their 5' non-coding regions; four contain an intron of different lengths, whereas the other two pos sess no intron. Ribonuclease protection analyses revealed that multipl e promoters are scattered throughout the upstream region, and the usag e of these different promoters together with alternative splicing lead s to a family of T/EBP messenger RNA (mRNA) species. A similar pattern of expression was also found in the human T/EBP gene expressed in a l ung carcinoma cell line. Longer T/EBP mRNAs are more abundant in rat F RTL-5 thyroid cells maintained in the absence of TSH (-TSH) than in ce lls maintained in the presence of TSH (+TSH). Transfection analyses us ing the rat T/EBP gene DNA upstream of the ATG initiation codon connec ted to the luciferase reporter plasmid showed a similar relative activ ity profile between -TSH and +TSH culture conditions, suggesting that the abundance of longer mRNAs in -TSH conditions may not directly corr elate with differences in promoter activities. Rather, TSH status migh t have a role in maintaining the physiological state of the cells. The upstream DNA of the rat and human T/EBP genes share a cluster of high and low sequence similarities, and both possess respectively 24 and 1 8 putative T/EBP-binding sites throughout. Cotransfection analyses of the T/EBP promoter-reporter constructs with a T/EBP expression vector into human HepG2 cells, which do not express T/EBP, suggested that aut oregulation may be involved in controlling both rat and human T/EBP ge ne expression.