Role of positive and negative regulation in modulation of the Fer promoter activity.

Abstract

p94(fer) is a cytoplasmic and nuclear tyrosine kinase whose function has been linked to cell growth. p94(fer) accumulates at different levels in various cell types and is not detected in pre-B, pre-T and T-cells (Halachmy, S., Bern, O., Schreiber, L., Carmel, M., Sharabi, Y., Shoham, J., Nir, U., 1997. p94(fer) facilitates cellular recovery of gamma irradiated pre-T cells. Oncogene 14, 2871-2880). The fer RNA, encoding p94fer, is transcribed from the FER locus in human rat and mouse. In the present work, a Fer gene transcription initiation point was determined, and the Fer promoter was cloned. A DNA genomic fragment, extending 3698bp upstream of the fer RNA start site, was isolated, sequenced and functionally characterized. A transient transfection assay, carried out in fibroblastic cell lines, revealed the presence of the Fer promoter within the cloned genomic fragment. The Fer promoter contains neither an obvious 'TATA' element nor a putative initiator sequence, but is composed of positive and negative, cis-acting elements. Negative regulation was found to be the main cause for dysfunctioning of the Fer promoter in a T-cell leukemia cell line (Jurkat). The minimal Fer promoter that is still active in fibroblasts consists of an AP1 binding site located 14bp upstream of the fer transcription initiation point. This minimal promoter was not active in the Jurkat T-cell leukemia cells and did not bind AP1 in these cells. Three additional AP1 sites were identified in functional sequences of the Fer promoter. Thus, the availability of AP1 activity may contribute as well to the modulation of the Fer promoter activity. The presumed regulatory role of AP1 in modulating the Fer promoter activity implies a link between cell growth and the Fer gene expression level. Indeed, exposure of fibroblasts to low serum growth conditions reduced the cellular level of the fer RNA.