Increase of GKLF messenger RNA and protein expression during progression of breast cancer

Genetic alterations found in carcinomas can alter specific regulatory pathw ays and provide a selective growth advantage by activation of transforming oncogenes, A subset of these genes, including wild-type alleles of GLI or c -MYC, and activated alleles of RAS or beta -catenin, exhibit transforming a ctivity when expressed in diploid epithelial RK3E cells in vitro. By in vit ro transformation of these cells, the zinc finger protein GKLF/KLF-4 was re cently identified as a novel oncogene, Although GKLF is normally expressed in superficial, differentiating epithelial cells of the skin, oral mucosa, and gut, expression is consistently up-regulated in dysplastic epithelium a nd in squamous cell carcinoma of the oral cavity, In the current study, we used in situ hybridization, Northern blot analysis, and immunohistochemistr y to detect GKLF at various stages of tumor progression in the breast, pros tate, and colon. Overall, expression of GKLE mRNA was detected by in situ h ybridization in 21 of 31 cases (68%) of carcinoma of the breast. Low-level expression of GKLF mRNA was observed in morphologically normal (uninvolved) breast epithelium adjacent to tumor cells. Increased expression was observ ed in neoplastic cells compared with adjacent uninvolved epithelium for 14 of 19 cases examined (74%), Ductal carcinoma in situ exhibited similar expr ession as invasive carcinoma, suggesting that GKLF is activated prior to in vasion through the basement membrane. Expression as determined by Northern blot was increased in most breast tumor cell lines and in immortalized huma n mammary epithelial cells when these were compared with finite-life span h uman mammary epithelial cells. Alteration of GKLF expression was confirmed by the use of a novel monoclonal antibody that detected the protein in norm al and neoplastic tissues in a distribution consistent with localization of the mRNA. In contrast to most breast tumors, expression of GKLF in tumor c ells of colorectal or prostatic carcinomas was reduced or unaltered compare d with normal epithelium, The results demonstrate that GKLF expression in e pithelial compartments is altered in a tissue-type specific fashion during tumor progression, and suggest that increased expression of GKLF mRNA and p rotein may contribute to the malignant phenotype of breast tumors.