GLIPR1 and melanoma: The low level of migration and complete lack of invasion in melanoma cells with relatively lower GLIPR1 levels (NZM15, NZM12, and NZM45) suggests that a threshold level of GLIPR1 expression may be present in melanoma cells with a strongly invasive phenotype as GLIPR1 levels in NZM9, NZM40, U251, and SNB75 cells after siRNA-mediated knockdown were still higher than that in untreated and weakly invasive NZM15, NZM12, and NZM45 cells.