Alternative promoters direct tissue-specific expression of the mouse protein phosphatase 2C beta gene

Type 2C protein phosphatases (PP2Cs), a class of ubiquitous and evolutional ly conserved serine/threonine protein phosphatases, are encoded in at least four distinct genes and implicated in the regulation of various cellular f unctions. Of these four PP2C genes, the expression of the PP2C beta gene ha s been reported to be tissue-specific and development-dependent. To underst and more precisely the regulatory mechanism of this expression, we have iso lated and characterized overlapping mouse genomic lambda clones. A comparis on of genomic sequences with PP2C beta cDNA sequences provided information on the structure and localization of intron/exon boundaries and indicated t hat PP2C beta isoforms with different 5' termini were generated by alternat ive splicing of its pre-mRNA. The 5'-flanking region of exon 1 had features characteristic of a housekeeping gene: it was GC-rich, lacked TATA bares a nd CAAT boxes in the standard positions, and contained potential binding si tes for the transcription factor SP1. In the 5'-flankin,a region of exon 2, several consensus sequences were found, such as a TATA-like sequence and n egative regulatory element box-1, -2 and -3. Subsequent analysis by transie nt transfection assay with a reporter gene showed that these regions act as distinct promoters. Analysis of PP2C beta transcripts by reverse transcrip tase-PCR showed that exon-l transcripts were expressed ubiquitously in all of the tissues examined, whereas exon-2 transcripts were predominantly expr essed in the testis, intestine and liver. These results suggest that the al ternative usage of two promoters within the PP2C beta gene regulates tissue -specific expression of PP2C beta mRNA.