Identification of nucleolar protein No55 as a tumour-associated autoantigen in patients with prostate cancer

Four different genes were identified by immunoscreening of a cDNA expressio n library from the human prostate cancer cell line DU145 with allogeneic se ra from four prostate cancer patients. A cDNA encoding the nucleolar protei n No55 was further analysed and shown to be expressed at the mRNA level in several normal tissues, including ovaries, pancreas and prostate and in hum an prostate cancer cell lines PC-3, PC-3m and LNCaP. By reverse transcripta se/polymerase chain reaction, expression of No55 was several-fold higher in two out of nine prostate cancer primary tumours and two out of two metasta tic lesions, compared to normal prostate tissue. Antibodies to No55 were de tected in sera from seven out of 47 prostate cancer patients but not in ser a from 20 healthy male controls. Sequence analysis of the No55 open reading frame from normal and tumour tissues revealed no tumour-specific mutations . The No55 gene was located to chromosome 17q21, a region reported to be pa rtially deleted in prostate cancer. Considering the immunogenicity of the N o55 protein in the tumour host, the expression profile and chromosomal loca lization of the corresponding gene, studies evaluating No55 as a potential antigen for immunological studies in prostate cancer may be warranted. (C) 2000 Cancer Research Campaign.