The influence of a highly polymorphic CA dinucleotide repeat in the epidermal growth factor receptor (EGFR) gene on transcription was examined with a quantitative nuclear run-off method. We could demonstrate that transcription of the EGFR gene is inhibited by approximately 80% in alleles with 21 CA repeats. In experiments with polymerase chain reaction products that spanned a region of more than 4,000 base pairs and contained the promoter, two enhancers, and the polymorphic region in the first intron of the gene, we found that transcription activity declines with increasing numbers of CA dinucleotides. In vivo pre-mRNA expression data from cultured cell lines support these findings, although other regulation mechanisms can outweigh this effect. In addition, we showed that under our experimental conditions RNA elongation terminates at a site closely downstream of the simple sequence repeat and that there are two separate major transcription start sites. Our results provide new insights in individually different EGFR gene expression and the role of the CA repeat in transcription of this proto-oncogene.

Breast biology and pathology are currently shaped by the two-cell concept that recognizes only glandular and myoepithelial cells. In the present study, we have visualized a previously unidentified cell population within the epithelial compartment of the breast, which displays the phenotypic characteristics of a committed stem cell. Immunofluorescence double labeling with digital image processing and Western blotting were applied to normal breast tissue as well as to noninvasive and invasive breast cancers using antibodies to basal cytokeratin 5 (Ck5), glandular cytokeratins 8/18 (Ck8/18/19), and smooth muscle α-actin (SMA) as markers for myoepithelial cells (SMA). A distinct population of cells was identified that expressed Ck5 in the absence of Ck8/18/19 or SMA. These cells differentiate toward glandular epithelial or myoepithelial Ck5-negative end cells passing through either Ck5/Ck8/18/19 or Ck5/SMA-positive intermediates. Our experiments clearly demonstrate a precursor or committed stem cell function of the Ck5-positive cell that is responsible for regeneration of the human adult breast epithelium. However, the observation that the vast majority of breast cancers display the glandular epithelial immunophenotype strongly suggests that the neoplastic cells derive from a late stage of the glandular epithelial differentiation pathway. The significance of this new cell biological model is that it might serve as a tool to unravel the regulatory mechanisms that govern regeneration and abnormal proliferation of breast epithelium at the cellular level.

Purpose: Early metastasis in node-negative breast cancer indicates that breast cancer cells obviously can bypass the lymph nodes and disseminate directly hematogenous to distant organs. For this purpose, we evaluated the prognostic value of blood-borne, HER2-positive circulating tumor cells (CTC) in the peripheral blood from 42 breast cancer patients with a median follow-up of 95 months.