A growing family of dual specificity phosphatases with low molecular masses.
Five putative dual specificity protein phosphatases (DSPs), designated LMW-DSP1, -DSP4, -DSP6, -DSP10, and -DSP11, were cloned with a combination of RT-PCR and cDNA library screening strategies. Sequencing analysis revealed that all lacked the cdc25 homology domain that is conserved in most known DSPs/MAP kinase phosphatases (MKPs). LMW-DSP1 exhibited the highest similarity to plant DSPs. LMW-DSP4 exhibited the highest similarity to human YVH1 and rat GKAP, but its C-terminal region was much shorter than that of the human and rat clones. LMW-DSP6 was found to be identical to recently cloned TMDP, and LMW-DSP11 seemed to be a mouse ortholog of human VHR. LMW-DSP10 was found to have a DSP catalytic-like domain, but the critical cysteine residue for catalytic activity was missing. Recombinant LMW-DSP1, -DSP6, and -DSP11 exhibited obvious and strong activity against an artificial low molecular substrate, para-nitrophenyl phosphate (pNPP). Recombinant LMW-DSP4 exhibited slight but significant activity, whereas no activity was detected for LMW-DSP10. The phosphatase activity of the recombinant LMW-DSPs was inhibited by orthovanadate but not sodium fluoride. However, none of the DSPs could dephosphorylate MAP kinases such as ERK1, p38, and SAPK/JNK in transiently transfected COS7 cells under the conditions used. Northern blot analysis revealed that LMW-DSP1, -DSP6, -DSP10, and -DSP11 were specifically expressed in testis, while LMW-DSP4 was broadly expressed. The testis-specific expression and apparent absence of dephosphorylation action on MAP kinases suggest that LMW-DSP1, -DSP6, -DSP10, and -DSP11 play specific roles in testis. Taken together, it is conceivable that a distinct class of low molecular mass DSPs is present and plays a role in dephosphorylating unknown molecules other than MAP kinases.
Aoki
N
N
Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. naoki@agr.nagoya-u.ac.jp
Aoyama
K
K
Nagata
M
M
Matsuda
T
T
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D019556:COS Cells; D002384:Catalysis; D003001:Cloning, Molecular; D020869:Gene Expression Profiling; D006801:Humans; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009596:Nitrophenols / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D009596:Nitrophenols; D009943:Organophosphorus Compounds; D012333:RNA, Messenger; C008644:nitrophenylphosphate; D020928:Mitogen-Activated Protein Kinases; D010744:Phosphoric Monoester Hydrolases