Chromatin structure of the regulatory regions of pS2 and cathepsin D genesin hormone-dependent and -independent breast cancer cell lines

We have compared the DNase I hypersensitivity of the regulatory region of t wo estrogen-regulated genes, pS2 and cathepsin D in hormone-dependent and - independent breast carcinoma cell lines. This strategy allowed the identifi cation of two important control regions, one in pS2 and the other in cathep sin D genes, In the hormone-dependent MCF7 cell line within the pS2 gene 5' -flanking region, we detected two major DNase I hypersensitive sites, induc ed by estrogens and/or IGFI: pS2-HS1, located in the proximal promoter and pS2-HS4, located -10.5 Kb from the CAP site, within a region that has not b een cloned. The presence of these two DNase I hypersensitive sites correlat es with pS2 expression. Interestingly in MCF7 cells, estrogens and IGFI ind uced indistinguishable chromatin structural changes over the pS2 regulatory region, suggesting that the two transduction-pathways converge to a unique chromatin target, In two cell lines that do not express pS2, MDA MB 231, a hormone-independent cell line that lacks the estrogen receptor alpha, and HE5, a cell line derived from MDA MB 231 by transfection that expresses est rogen receptor alpha, there was only one hormone-independent DNase I hypers ensitive site. This site, pS2-HS2, was located immediately upstream of pS2- HS1, In MCF7 cells, two major DNase I hypersensitive sites were present in the 5'-flanking sequences of the cathepsin D gene, which is regulated by es trogens in these cells. These sites, catD-HS2 and catD-HS3, located at posi tions -2.3 Kb and -3.45 Kb, respectively, were both hormone-independent. A much weaker site, catD-HS1, covered the proximal promoter. In MDA MB 231 ce lls, that express cathepsin D constitutively we detected an additional stro ng hormone-independent DNase I hypersensitive site, catD-HS4, located at po sition -4.3 Kb, This region might control the constitutive over-expression of cathepsin D in hormone-independent breast cancer cells, All together, th ese data demonstrate that a local reorganization of the chromatin structure over pS2 and cathepsin D promoters accompanies the establishment of the ho rmone-independent phenotype of the cells.