SPHK1 and Familial prostate cancer: LNCaP prostate cancer cells express two N-terminal variant isoforms of SK1: SK1a (GenBank number: NM_001142601), which is a 42.5-kDa protein, and SK1b (GenBank number: NM_182965), which is a 51-kDa protein identical to SK1a but has an 86 amino acid N-terminal extension (sometimes referred to as SK1c).