Expression and regulation of the meprin β gene in human cancer cells

A novel mRNA isoform (meprin β') of the cell-surface protease subunit meprin β was previously identified in human colon cancer cells. The study reported here revealed that this mRNA isoform was identical within the protein coding region and at the 3' end to the β isoform of normal intestine but that it contained an extended 5' untranslated region. Meprin β' mRNA was expressed in the human breast cancer cell lines MCF-7 and SK-BR-3, in the human osteosarcoma cell line U2 Os, and in the human pancreatic cancer cell line BxPC-3. Meprin β mRNA, but not β' mRNA, was expressed in human fetal kidney cells. We cloned and sequenced genomic DNA encoding portions of the promoter region of the meprin β gene. The unique sequences present in the β' mRNA were present in the human genomic DNA immediately upstream of the transcription start site for the β mRNA. The human meprin promoter sequence was searched for potential transcription-factor binding sites, and putative activator protein-1, polyoma enhancer activator 3 (PEA3), CCAAT enhancer- binding protein beta, and estrogen-receptor binding sites were identified along with binding sites for the intestine-specific cdx-2 transcription factor. The activity of meprin promoter/luciferase reporter gene constructs transfected into U2 Os cells was highest with constructs containing 83 and 639 bp of promoter DNA. These regions of the promoter each contain a putative PEA3 element. Treatment of the human colon adenocarcinoma cell line HT29- 18C₁ with 50 or 100 ng/mL phorbol myristal acetate for 8 h increased meprin β' mRNA levels. Likewise, U2 Os cells transfected with the -639/luciferase or -1800/luciferase constructs showed a phorbol myristal acetate-inducible increase in reporter gene activity, indicating that the PEA3 element within the -639 construct or other elements further upstream respond to phorbol ester.