TISSUE EXPRESSION OF NEU DIFFERENTIATION FACTOR HEREGULIN AND ITS RECEPTOR COMPLEX IN PROSTATE-CANCER AND ITS BIOLOGIC EFFECTS ON PROSTATE-CANCER CELLS IN-VITRO

BACKGROUND Prostate cancer is the most common cancer in American men a nd the second leading cause of cancer death. All clinical observations correlate poorly differentiated high-grade prostate cancer with disea se-specific mortality. The HER2 cell membrane tyrosine kinase, a membe r of the epidermal growth factor receptor family that is the transcrip tion product of the erB2(neu) oncogene, and HER3, a receptor protein o f the same family, are overexpressed in prostate cancer and prostatic intraepithelial neoplasia. The ligand for these receptors and another related family member, HER4, has recently been identified by independe nt investigator groups and called neu differentiation factor (NDF) or heregulin. In vitro treatment of HER2- and HER3- or HER2- and HER4-exp ressing breast cancer cells stimulates tyrosine phosphorylation of HER 2 and produces changes in the rate of proliferation, degree of cellula r differentiation, and synthesis of physiologic secretion products. Th ere are no published reports on the expression of NDF and HER4 in pros tate cancer or the in vitro effects of NDF in prostate cancer cells. M ETHODS Expression of NDF, HER2, HER3, and HER4 was studied in 24 froze n prostatectomy specimens by immunohistochemistry. The biologic effect of human recombinant NDF was studied in vitro, using the LNCaP, PC3, and DU145 human prostate cancer cell lines. HER and NDF protein expres sion was studied by immunohistochemistry. NDF mRNA was analyzed using reverse transcriptase polymerase chain reaction from whole RNA. The bi ologic effects of NDF on prostate cancer cells in vitro included cell proliferation, thymidine synthesis, induction of prostate-specific ant igen mRNA, anchorage-dependent and anchorage-independent cell growth, and ploidy analysis. Data analysis was performed using Student's t tes t. RESULTS Observations in clinical prostatectomy specimens: Immunohis tochemistry studies in clinical prostatectomy specimens demonstrate ab sence of significant NDF expression in prostate cancer, whereas it is expressed in 100% of the stroma, 100% of basal epithelial cells, and 5 8% of luminal cells in normal and benign hyperplastic prostatic tissue . The HER4 receptor protein is strongly expressed by normal prostate l uminal cells, but not prostate cancer. Benign prostate tissue exhibits strong expression of HER2, HER3, and HER4 by basal cells, but only lu minal cells significantly express HER4. Only 23% of prostate cancer sp ecimens express HER4, while 95% express HER3 and 82% HER2. Prostatic i ntraepithelial neoplasia stained similarly to cancer for all proteins studied. Observations in prostate cancer cell lines: In vitro treatmen t with NDF significantly reduces aneuploidy and proliferation and grow th of androgen-sensitive prostate cancer cells. Incubation with NDF al so induces prostate-specific antigen mRNA in prostate cancer cells. In spite of displaying NDF mRNA, prostate cancer cells do not produce de tectable NDF protein, but express HER2 and HER3 proteins. DISCUSSION T hese data suggest that NDF may be a paracrine differentiation factor i nvolved in normal adult prostate physiology and that functional loss o f the NDF/HER ligand/receptor loop may be an early went associated wit h prostate tumorigenesis.