Compositions and methods are provided for the treatment of conditions associated with cell proliferation, cell differentiation and cell survival. In particular, the dual-specificity phosphatase DSP-10, and polypeptide variants thereof that stimulate dephosphorylation of DSP-10 substrates, are provided. The polypeptides may be used, for example, to identify antibodies and other agents that inhibit DSP-10 activity. The polypeptides and agents may be used to modulate cell proliferation, differentiation and survival.