The invention discloses a novle human vacuolar H⁺-ATPase C subunit 42 and a polynucleotide encoding it. The invention also concerns a process of producing the polypeptide by recombinant DNA techniques. Methods are also disclosed for treating many diseases, e.g. malignant tumors, hemopathies, HIV infections, immune diseases and inflammations utilizing the ploypeptide. The invention discloses antagonists of the polypeptide and therapeutics comprising the same. The invention also discloses the uses of the polynucleotide, which encodes the human vacuolar H⁺-ATPase C subunit 42.