COL1A1 proximal promoter topology regulates its transcriptional response to transforming growth factor β.

objectiveThe COL1A1 proximal promoter contains two GC-rich regions and two inverted CCAAT boxes. The transcription factors Sp1 and CBF bind to the GC sequence at -122 to -115 bp and the inverted CCAAT box at -101 to -96 bp, respectively, and stimulate COL1A1 transcriptional activity.

methodsTo further define the regulatory mechanisms controlling COL1A1 expression by Sp1 and CBF, we introduced 2, 4, 6, or 8 thymidine nucleotides (T-tracts) at position -111 bp of the COL1A1 gene promoter to increase the physical distance between these two binding sites and examined

resultsInsertion of 2 or 4 nucleotides decreased COL1A1 promoter activity by up to 70%. Furthermore, the expected increase in COL1A1 transcription in response to TGF-β1 was abolished. Computer modeling of the modified DNA structure indicated that increasing the physical distance between the Sp1 and CBF binding sites introduces a rotational change in the DNA topology that disrupts the alignment of Sp1 and CBF binding sites and likely alters protein-protein interactions among these transcription factors or their associated co-activators.

conclusionThe topology of the COL1A1 proximal promoter is crucial in determining the transcriptional activity of the gene and its response to the stimulatory effects of TGF-β1.