High FKBP51 expression is accompanied by increased metastatic potential. A, Real-time PCR measurement of FKBP51, TβRIII, and TGF-β mRNAs in A375 melanoma cells, which were silenced (FKBP51 siRNA) or not (NS RNA) for FKBP51. The relative change of expression in A375 samples was estimated relative to SAN samples (expression = 1). Reduced mRNA levels in FKBP51-silenced A375 confirmed that the immunophilin regulated the expression of TβRIII, and TGF-β in melanoma. B, FDG PET coronal views of mouse models of melanoma metastasis, 21 days after iv injection of two different cell lines: A375 (left) and SAN (right). FDG PET imaging show a diffuse and more prominent FDG uptake (mostly at lung and liver level, yellow squares) in the left mouse, suggesting that A375 have enhanced tumorigenic potential compared with SAN.