Abundant cysteine-rich protein-1 is localized in the stromal compartment of the human prostate

The cysteine-rich protein-1 (CRP1) is one of the major proteins of the human prostate. Because of the suspected importance of that protein in cell proliferation and differentiation, its expression was investigated in the prostate, prostatic cancer cells, and other organs of the body. At the mRNA level, the highest concentrations of CRP1 were found in the prostate and the colon followed by the brain and the testis. It was virtually absent from the spleen, liver, heart, and kidney. Prostatic cancer cells PC-3, DU-145, and LNCaP also expressed CRP1 mRNA but virtually no protein. CRP1 protein localization in tissues was determined by immunohistochemical analysis using polyclonal antibodies developed against recombinant CRP1 protein. Strong positive cytoplasmic immunoreactions were observed only in the stromal compartment of the prostate and of other smooth muscle-rich tissues without significant staining in any secretory epithelium. These results, along with previously reported data of colocalization of CRP1 with stress fibers and adhesion plaques, suggest that the main function of CRP1 may be structural.