Mapping of the gene encoding the B56 beta subunit of protein phosphatase 2A (PPP2R5B) to a 0.5-Mb region of chromosome 11q13 and its exclusion as a candidate gene for multiple endocrine neoplasia type 1 (MEN1)

Genomic organization and precise physical location of protein phosphatase 2A regulatory subunit A beta isoform gene on chromosome band 11q23

Protein phosphatase 2A (PP2A) holoenzyme plays a critical role in cell-cycle control and growth-factor signaling, and is implicated in tumorigenesis. Because the protein phosphatase 2 regulatory subunit A beta isoform gene (PPP2R1B) maps within the critical region of hereditary paraganglioma (PGL1) on chromosomal band 11q23, we characterized its genomic structure and evaluated it as a candidate gene for PGL1. PPP2R1B has 15 exons spanning approx. 27kb genomic distance. We placed the exons on genomic EcoRI fragments and identified their flanking intronic sequences. The gene was oriented from telomere to centromere. Splice acceptor and donor sites of all introns conformed to the GT/AG rule. Northern analysis with a cDNA probe identified 2.5kb and 5.0kb transcript sizes. We identified an ATG initiation codon in a favorable context and mapped two transcription start sites 15bp and 66bp upstream of it. We also mapped a 3'-polyadenylation site 504bp downstream of the TGA stop codon, consistent with the 2.5kb transcript size. We did not detect germ-line mutations by single-stranded conformational polymorphism (SSCP) analysis or major rearrangements by Southern analysis in a set of PGL1 patients. In conclusion, we precisely mapped and characterized the structure of PPP2R1B and evaluated it as a candidate gene for PGL1.