Cloning,Chromosome Mapping And Functional Study Of Pig SREBPs And CREB-1

SREBPs (sterol regulatory element binding proteins) and CREB-1 (cAMP response element binding protein) are the important transcriptional factors in vivo. SREBPs mainly regulate fatty acid and cholesterol synthesis and CREB-1 has the more extensive activation. The SREBPs family has three proteins: SREBP-la, SREBP-lc and SREBP-2. In human, SREBP-2 is derived from the chromosome 22; SREBP-la and SREBP-lc are from the same gene on the chromosome 17, they have the same exons except the first exon due to the utilization of different promoters. SREBP-lc preferentially enhances transcription of genes required for fatty acid synthesis; SREBP-2 has a long transcriptional activation domain, but it preferentially activates cholesterol synthesis. In this study, the partial SREBP-2 CDS and the complete CREB-1 CDS have been acquired. Comparing the human and Chinese hamster SREBP-2 nucleotide sequences with the pig SREBP-2, the similarity can get 95.1% and 96.8% respectively. Pig CREB-1 shows 95.1% and 96.8% identity with the human and the house mouse CREB-1 nucleotide sequences. Pig SREBP-lc nucleotide sequence has been reported and shows 88.5% and 78.8% identity with human and house mouse SREBP-lc nucleotide sequence respectively. It can be concluded that these three genes are highly conserved during evolution. Pig SREBP-2 gene has been successfully assigned at the distal end of the chromosome 5. The result is consistent with comparative map between human and pig. The tissue distributions of these three genes are also been studied using the semi-quantitative Real-Time PCR in ten different tissues from the Meishan pig. The results demonstrate that three genes are expressed ubiquitously, SREBP-1 is mainly expressed in the adipose tissue and SREBP-2, CREB-1 is in liver and brain,respectively. In the pig lipogenic organ-adipose tissue, SREBP-1 shows the higher expression than SREBP-2.Besides, the expression regulation of SREBPs is studied by transfection and drugs stimulation. It has been reported that clenbuterol, a kind of the 8-agonist, is able to increase the expression of CREB-1 and inhibit the fatty acid production. In the COS7 cell line, which is stimulated by the drug clenbuterol, CREB-1 is expressed higher in the level as expected, but the expressions of SREBPs descend. While in the 293T cell line, where CREB-2 is transfected, a natural inhibitor of CREB-1, the expressions of SREBPs is elevated. The results suggest that the fatty acid metabolism pathway mediated by CREB-1 should be related with SREBPs.