SPHK1 and head and neck squamous cell carcinoma: In the present study, we found that miR-124 acted as a tumor suppressor in HNSCC via directly inhibiting the expression of sphingosine kinase 1 (SphK1), a core enzyme that regulates the ceramide-sphingosine-sphingosine-1-phosphate (S1P) interconversion, ultimately directing cells towards an apoptotic program in HNSCC.