This subfamily contains dual specificity protein phosphatase 18 (DUSP18), dual specificity protein phosphatase 21 (DUSP21), and similar proteins. They function as protein-serine/threonine phosphatases (EC 3.1.3.16) and protein-tyrosine-phosphatases (EC 3.1.3.48), and are atypical DUSPs. They contain the catalytic dual specificity phosphatase domain but lack the N-terminal Cdc25/rhodanese-like domain that is present in typical DUSPs or MKPs. DUSP18, also called low molecular weight dual specificity phosphatase 20 (LMW-DSP20), is a catalytically active phosphatase with a preference for phosphotyrosine over phosphoserine/threonine oligopeptides in vitro. In vivo, it has been shown to interact and dephosphorylate SAPK/JNK, and may play a role in regulating the SAPK/JNK pathway. DUSP21 is also called low molecular weight dual specificity phosphatase 21 (LMW-DSP21). Its gene has been identified as a potential therapeutic target in human hepatocellular carcinoma. DUSP18 and DUSP21 target to opposing sides of the mitochondrial inner membrane.
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