Protein tyrosine phosphatase type IVA 1(PTP4A1) is a cell signaling molecule that has regulatory roles in a variety of cellular processes. PTP4A1 is a unique nuclear PTP which is induced in regenerating liver and mitogen stimulated cells. PTP4A1 is primarily expressed in the spleen, bone marrow, thymus, lymph nodes, T lymphocytes and tonsil and is overexpressed in tumor cell lines.