Identification of an intronic enhancer that nullifies upstream repression of SPARC gene expression

The SPARC gene 5' flanking sequence has been shown to contain enhancer elements, but also negative control elements immediately upstream of the enhancer elements. Although these 5' enhancer elements are active in F9 and PYS-2 cells, their activities are nullified by the 5' repressor activity. In the present study we have identified within intron 1 between nucleotides (nt) +5000 and +5150 of the SPARC gene an enhancer element that bound to two transcription factors of 48 and 52 kDa and between nt +5000 and +5523 a DNase l hypersensitive site. Furthermore, a region containing the 3' intron 1 enhancer element, together with the 5' enhancer elements, neutralized the 5' repressor activity and stimulated efficient transcription. The resulting SPARC promoter activity is about equal in F9, differentiated F9 and PYS-2 cells. We consistently found that the rate of SPARC transcription is nearly the same in F9 and PYS-2 cells. Association of the 3' enhancer element in intron 1 with the DNase I hypersensitive site suggests that both play a role in regulating SPARC expression in vivo.