Protein tyrosine phosphatase which stimulates progression from G1 into S phase during mitosis. May play a role in the development and maintenance of differentiating epithelial tissues. Enhances cell proliferation, cell motility and invasive activity, and promotes cancer metastasis. {ECO:0000269|PubMed:12235145, ECO:0000269|PubMed:12782572, ECO:0000269|PubMed:14643450}. This is the function of ENSG00000112245 (PTP4A1, protein tyrosine phosphatase 4A1).