Localization of the mouse protein serine/threonine phosphatase 2C beta gene to chromosome 17E 4-5

The role of PP5 and PP2C in cardiac health and disease

Protein phosphatases are important, for example, as functional antagonists of β-adrenergic stimulation of the mammalian heart. While β-adrenergic stimulations increase the phosphorylation state of regulatory proteins and therefore force of contraction in the heart, these phosphorylations are reversed and thus force is reduced by the activity of protein phosphatases. In this context the role of PP5 and PP2C is starting to unravel. They do not belong to the same family of phosphatases with regard to sequence homology, many similarities with regard to location, activation by lipids and putative substrates have been worked out over the years. We also suggest which pathways for regulation of PP5 and/or PP2C described in other tissues and not yet in the heart might be useful to look for in cardiac tissue. Both phosphatases might play a role in signal transduction of sarcolemmal receptors in the heart. Expression of PP5 and PP2C can be increased by extracellular stimuli in the heart. Because PP5 is overexpressed in failing animal and human hearts, and because overexpression of PP5 or PP2C leads to cardiac hypertrophy and KO of PP5 leads to cardiac hypotrophy, one might argue for a role of PP5 and PP2C in heart failure. Because PP5 and PP2C can reduce, at least in vitro, the phosphorylation state of proteins thought to be relevant for cardiac arrhythmias, a role of these phosphatases for cardiac arrhythmias is also probable. Thus, PP5 and PP2C might be druggable targets to treat important cardiac diseases like heart failure, cardiac hypertrophy and cardiac arrhythmias.

Role of type 2C protein phosphatases in growth regulation and in cellular stress signaling

A number of interesting features, phenotypes, and potential clinical applications have recently been ascribed to the type 2C family of protein phosphatases. Thus far, 16 different PP2C genes have been identified in the human genome, encoding (by means of alternative splicing) for at least 22 different isozymes. Virtually ever since their discovery, type 2C phosphatases have been predominantly linked to cell growth and to cellular stress signaling. Here, we provide an overview of the involvement of type 2C phosphatases in these two processes, and we show that four of them (PP2Calpha, PP2Cbeta, ILKAP, and PHLPP) can be expected to function as tumor suppressor proteins, and one as an oncoprotein (PP2Cdelta /Wip1). In addition, we demonstrate that in virtually all cases in which they have been linked to the stress response, PP2Cs act as inhibitors of cellular stress signaling. Based on the vast amount of experimental evidence obtained thus far, it therefore seems justified to conclude that type 2C protein phosphatases are important physiological regulators of cell growth and of cellular stress signaling.

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

Type 2C protein phosphatases (PP2Cs), a class of ubiquitous and evolutionally conserved serine/threonine protein phosphatases, are encoded in at least four distinct genes and implicated in the regulation of various cellular functions. Of these four PP2C genes, the expression of the PP2Cbeta gene has been reported to be tissue-specific and development-dependent. To understand more precisely the regulatory mechanism of this expression, we have isolated and characterized overlapping mouse genomic lambda clones. A comparison of genomic sequences with PP2Cbeta cDNA sequences provided information on the structure and localization of intron/exon boundaries and indicated that PP2Cbeta isoforms with different 5' termini were generated by alternative 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 boxes and CAAT boxes in the standard positions, and contained potential binding sites for the transcription factor SP1. In the 5'-flanking region of exon 2, several consensus sequences were found, such as a TATA-like sequence and negative regulatory element box-1, -2 and -3. Subsequent analysis by transient transfection assay with a reporter gene showed that these regions act as distinct promoters. Analysis of PP2Cbeta transcripts by reverse transcriptase-PCR showed that exon-1 transcripts were expressed ubiquitously in all of the tissues examined, whereas exon-2 transcripts were predominantly expressed in the testis, intestine and liver. These results suggest that the alternative usage of two promoters within the PP2Cbeta gene regulates tissue-specific expression of PP2Cbeta mRNA.