Human Dual-specificity Phosphatase Dusp18 And Dusp23 Gene Cloning And Function

Dual-specificity protein phosphatases (DSPs), a new family of protein tyrosine phosphatases (PTPs), are characterized by the ability to dephosphorylate both phospho-tyrosyl and phospho-seryl/threonyl residues. It has been known that most of the enzymes play important roles in the regulation of mitogenic signal transduction and cell cycle control in response to extracellular stimuli. In this study, two novel human DSP gene named Dual-specificity Phosphatase18 (DUSP18) and Dual-specificity Phosphatase23 (DUSP23) were isolated by large-scale sequencing analysis of a human fetal brain cDNA library. DUSP18 cDNA is 2450 base pairs in length, encoding a 188-amino acid polypeptide and DUSP23 is 726 bp in length, encoding a 150-amino acid polypeptide. They all have a dual-specificity phosphatase catalytic (DSPc) domain but not a CDC25 homology (CH2) domain which exists in most of the DSPs.DUSP18 is widely expressed in different tissues and cell lines. DUSP23 is expressed in most fetal tissues and two adult tissues: testis and colon. The expression of DUSP18 is modulated in response to extracelluar stimuli whereas DUSP23 is not.Both DUSP18 and DUSP23 showed distinctive phosphatase activity toward p-nitrophenyl phosphate (pNPP), as well as oligopeptides containing pThr and pTyr, indicating that they are novel protein phosphatase with dual substrate specificity.By phosphorylation assay, pull down and coimmunoprecipetation experiments, DUSP23 was proved to be able to dephosphorylate p44ERK1 only in vitro but not in vivo. DUSP18 could interact with SAPK/JNK and dephosphorylate it both in vitro and in vivo. And DUSP18 does not dephosphorylate p38 or p44ERK1. Furthermore, DUSP18 inhibits SAPK/JNK pathway in vivo. Based on these findings, DUSP18 appears to serve an important role in regulation of SAPK/JNK pathway.Yeast two-hybrid screen showed DUSP18 might interacted with some other proteins including CyclinA, SGT1, PRA (S100A6), SKB1, Sam68 and TRK-fused gene. Using the yeast mating and pull down experiments, weconfirmed the interactions between S100A6(PRA) and DUSP18 as well as Cyclin A and DUSP18.In conclusion, we have cloned two novel human dual specificity phosphatases named DUSP18 and DUSP23. Functioned study revealed that DUSP18 may be an important regulatory factor of SAPK/JNK pathway in vivo. DUSP23 could dephosphorylate p44ERK1 in vitro but its actual function in vivo was not identified yet.