The present invention discloses a novel polypeptide--human actin-binding protein 54 and a polynucleotide encoding the same, as well as a method of producing the polypeptide by DNA recombinant technology. The present invention also discloses methods of using the polypeptide in treatment of various diseases, such as malignant tumor, blood disease, HIV infection, immunological diseases and various inflammation. The present invention also discloses an antagonist against the polypeptide and the therapeutic use of the same. The present invention also discloses the use of such polynucleotide encoding human actin-binding protein 54.