Characterization of Two Distinct Dual Specificity Phosphatases Encoded in Alternative Open Reading Frames of a Single Gene Located on Human Chromosome 10q22.2

Abstract

Dual specificity phosphatases (DSPs) are members of the protein-tyrosine phosphatase superfamily that dephosphorylate both phosphotyrosine and phosphoserine/threonine residues in vitro. Many DSPs have been found to play important roles in various aspects of cellular function and to be involved in human disease. We have identified a gene located on human chromosome 10q22.2, which utilizes alternative open reading frames (ORFs) to encode the following two distinct DSPs: the previously described testis and skeletal muscle-specific dual specificity phosphatase (TMDP) and a novel DSP, muscle-restricted dual specificity phosphatase (MDSP). Use of alternative ORFs encoding distinct proteins from a single gene is extremely rare in eukaryotes, and in all previously reported cases the two proteins produced from one gene are unrelated. To our knowledge this is the first example of a gene from which two distinct proteins of the same family are expressed using alternative ORFs. Here we provide evidence that both MDSP and TMDP proteins are expressed in vivo and are restricted to specific tissues, skeletal muscle and testis, respectively. Most interestingly, the protein expression profiles of both MDSP and TMDP during mouse postnatal development are strikingly similar. MDSP is expressed at very low levels in myotubes and early postnatal muscle. TMDP is not detectable in testis lysate in the first 3 weeks of life. The expression of both MDSP and TMDP proteins was markedly increased at approximately the 3rd week after birth and continued to increase gradually into adulthood, implying that the physiological functions of both DSPs are specific to the mature/late-developing organs. The conserved gene structure and the similarity in postnatal expression profile of these two proteins suggest biological significance of the unusual gene arrangement. Members of the protein-tyrosine phosphatase (PTP)1 superfamily are characterized by the presence of a signature motif (HCX 5 R) in their primary sequences. With the completion of the genome sequencing projects, we are now aware of ϳ100 PTP genes in the mammalian genomes. The PTP superfamily is roughly divided into two categories according to substrate specificity, the tyrosine-specific phosphatases and the dual specificity phosphatases (DSPs). The DSPs are operationally defined as members of the PTP superfamily that have the capability to dephosphorylate both phosphotyrosine and phosphoserine/threonine residues in vitro. Nevertheless, in terms of physiological function, the "DSPs" may actually show preference for either Ser/Thr (1, 2) or Tyr residues (3). Most interestingly, some DSPs even target nonprotein substrates such as phospholipids (4, 5) and RNA (6) in vivo. Although members of this family have been shown to play pivotal roles in various aspects of cell function, including signal transduction, actin polymerization, mRNA processing, cell cycle regulation, and apoptosis (7-9), the physiological functions of many DSPs remain to be elucidated.The prototypic DSP is VH1, a virulence fact...

Mitogen-Activated Protein (MAP) Kinase/MAP Kinase Phosphatase Regulation: Roles in Cell Growth, Death, and Cancer

“…These two proteins share 42% sequence identity. Interestingly, this locus has an ortholog in mouse and a similar arrangement of phosphatases in puffer fish (Fugu rubripes), indicating evolutionary conservation and perhaps importance (Chen et al, 2004). MDSP and TMDP display phosphatase activity toward phosphotyrosine and phosphothreonine when tested against artificial substrates.…”

“…Another twist in this story lies in the rare event in mammalian cells of two different proteins of the same family coded by the same gene as a result of different open reading frames, as is the case for DUSP13A (MDSP) and DUSP13B (TMDP) (Chen et al, 2004) (Table 2). These two proteins share 42% sequence identity.…”

Emerging Roles of Atypical Dual Specificity Phosphatases in Cancer

“…The dusp13 gene encodes for two similar protein products via alternative reading frames [120,121]. Designated DUSP13A and DUSP13B, the proteins are expressed in the muscle and testis respectively [121,122].…”

“…Designated DUSP13A and DUSP13B, the proteins are expressed in the muscle and testis respectively [121,122]. Both proteins have phosphatase activity in vitro, with DUSP13B exhibiting higher activity than DUSP13A [122].…”

Inhibition of DUSP13A Activity by PTP Inhibitor V

“…4,5 DUSP13 encodes DUSP13A/MDSP (muscle-restricted DUSP) and DUSP13B/ TMDP (testis-and skeletal muscle-specific DUSP) due to alternative splicing of the ORF. 3,6 DUSP13B is encoded by the downstream ORF. These two proteins share 42% identity in amino acid sequences.…”