PTEN and melanoma: ,26 To investigate whether lipid phosphatase activity of PTEN is required for inhibition of metastasis in vivo, we introduced the PTEN G129E (PTEN ΔL), wildtype PTEN (PTEN WT), or the PTEN phosphatase dead mutant C124S (PTEN ΔLP) into B16F1 melanoma cells.