passages.id: 8195215__text
passages.type: abstract
passages.text: An intricate arrangement of binding sites for the Ets family of transcription factors regulates activity of the alpha 4 integrin gene promoter. 
  alpha 4 integrins mediate cell-cell and cell-extracellular matrix interactions that are critical for maturation and function of the immune system as well as differentiation of skeletal muscle. Here we examine molecular mechanisms controlling the pattern of alpha 4 expression. The activity of constructs containing 5' deletion mutants of the alpha 4 gene promoter was compared in transfection assays into cell lines that express alpha 4 and cell lines that do not. The sequence between position -42 and -76 base pairs (bp) was required for efficient transcription in cells that express alpha 4, but it showed no activity in HeLa cells, which do not express alpha 4. Three binding sites for the Ets family of transcription factors are found in this region: two adjacent sites at positions -50 and -54 bp and a more 5' site at position -67 bp. Using a series of constructs containing deletions and mutations in this region, we found that the 3'-most site alone was sufficient for binding GA-binding protein alpha (GABP alpha)/GABP beta and for a low level of transcriptional activation. When all three sites were present, a second complex "a" was detected, which contains an unknown member of the Ets family. Formation of complex a was cell-type specific and correlated with a high level of transcription. Deletion of the 5'-most Ets site had no effect on binding to GABP alpha/GABP beta, but it eliminated a. Concomitant with this loss of a, a new Ets-1-containing complex "c" appeared. Complex c substituted efficiently for complex a in transcriptional activation. We conclude that although neither of the two 5'-most Ets sites alone binds nuclear protein, they appear to act as modulators which control the pattern of Ets proteins that bind the alpha 4 gene promoter. This arrangement of Ets sites, coupled with the tissue- and developmental-specific expression of Ets members, likely play a key role in defining the pattern of alpha 4 integrin. 