ATP6V1C1 and oral cavity squamous cell carcinoma: ATP6V1C1, an essential subunit of V-ATPase and a regulator of V-ATPase activity [6], [7], [8], [9], was recently reported to be the most strongly overexpressed gene in oral squamous cell carcinoma compared to other subunits of V-ATPase, and it was suggested to control tumor growth and metastasis [16].