RESUMO
The glycosylphosphatidylinositol-anchored molecule C4.4A, which shares structural features with uPAR, is frequently expressed on carcinomas with upregulated expression during tumor progression. Moreover, rare expression on nontransformed epithelial cells is strongly increased during tissue remodeling, e.g., during wound healing. This strictly regulated expression prompted us to define transcriptional activation of the C4.4A gene. C4.4A transcription was analyzed in 2 syngenic rat tumor cell lines with low or high metastatic potential, respectively. Though genomic C4.4A DNA was present in both lines, C4.4A mRNA and transcription of a reporter construct containing the C4.4A promoter was only observed in the metastasizing subline. Deletions and point mutations in the C4.4A promoter-driven reporter construct revealed that activation of the TATA-less, GC-rich core promoter (-1 to -50 bp) does not suffice to initiate transcription that requires coactivation of a proximal response element (-71 to -88 bp) and can be further increased by more distal response elements (-89 to -133 bp). Mobility-shift and cotransfection studies showed that Sp3 binding enhances C4.4A transcription, whereas potential Sp1 binding sites were ineffective. C4.4A transcription essentially requires C/EBPbeta binding to a TRE/CCAAT composite element (-71 to -88 bp) as measured by ChIP assay. C4.4A transcription is strikingly enhanced by cotransfection with JunD or c-Jun, such that C4.4A is most strongly transcribed even in the C4.4A-negative tumor cell line after cotransfection with C/EBPbeta plus JunD or c-Jun. Thus, upregulation of C/EBPbeta during tumor progression and wound repair may well provide a sufficient trigger for transcription of the C4.4A gene.
