Chantal Escot

The proto-oncogene c- fos increases the sensitivity of keratinocytes to apoptosis

In human skin, most studies have suggested a role of c-fos or c-fos related genes in keratinocyte differentiation. The aim of our work was to more directly address this question by transfecting more or less differentiated keratinocyte cell lines (A431 and HaCaT) with constitutive expression vectors for c-Fos or c-Fos+c-Jun. Our results showed that c-Fos expression decreased keratinocyte growth, yet addition of c-Jun seemed to revert this c-Fos induced growth inhibition. Whereas no obvious differentiation program was turned on by c-Fos or c-Fos+c-Jun expression in our tissular model, apoptotic figures were observed and confirmed by in situ DNA fragmentation studies. These results do not rule out a role of c-Fos in keratinocyte differentiation but may indicate that the cell lines we used have reached an irreversible state of transformation so that they no longer respond to differentiation signals and rather die from apoptosis. These data add further evidence in favor of a role of c-Fos in epidermal homeostasis.

Cellular localisation byin situ hybridisation of cathepsin D, stromelysin 3, and urokinase plasminogen activator RNAs in breast cancer

SummaryWe have compared by RNAin situ hybridisation on serial cryo-sections the distribution of cathepsin D (cath-D), stromelysin 3 (strom-3), and urokinase plasminogen activator (UPA) gene expression in different tissues of human benign and malignant mammary tumors. Cath-D expression was found to be higher in adenocarcinomas compared to non-tumoral glands. The cath-D RNA was located in mammary epithelial cancer cells rather than in fibroblasts, indicating that the cath-D gene was overexpressed in cancer cells, where the corresponding protein determined by immunohistochemical staining had been shown to be accumulated (P. Rogeret al., Human Pathol 25: 863–871, 1994). In contrast strom-3 RNA in adjacent tissue sections used as a control of tissue localisation was mostly expressed in peritumoral fibroblasts rather than in cancer cells confirming previous results of Bassetet al. and validating our methodology. UPA RNA was detected both in tumor cells and in stromal cells. In benign lesions the 3 protease RNAs were mostly found in epithelial cells. Stromal cells expressed UPA RNA in 5 of 7 lesions, cath-D and strom-3 in only one sample.We conclude that in breast cancer patients, cath-D gene expression is increased in epithelial mammary cancer cells at the RNA level as well as at the protein level, suggesting an altered transcriptional regulation. In non malignant lesions, the distribution was different with a predominant distribution in epithelial mammary cells for the 3 protease messenger RNA.

In vivo stimulation by tamoxifen of cathepsin D RNA level in breast cancer

We have previously shown that 3 weeks of treatment with tamoxifen, of patients with primary breast carcinomas, increased cytosolic cathepsin D protein in oestrogen receptor (ER) positive tumours [Maudelonde et al., Cancer 1989, 63, 1265-1270]. In order to investigate the mechanism of this increase and to eliminate a transient flare-up effect, we semi-quantified cathepsin D RNA levels by in situ hybridisation in 32 breast carcinomas from patients treated with tamoxifen for 3 weeks prior to surgery and in 35 breast cancer patients receiving no tamoxifen. We found that tamoxifen increased cathepsin D RNA level regardless of the ER status of the tumours. In ER positive tumours, tamoxifen increased the cathepsin D RNA level to the same extent as cytosolic cathepsin D protein but not in ER negative tumours. The induction of cathepsin D RNA by tamoxifen in ER positive tumours was probably due to its agonist activity, also observed in vitro in breast cancer cell lines. These results suggest that the cathepsin D gene is inducible by oestrogens in ER positive breast cancer as it is in breast cancer cell lines.

Progestin-induced fatty acid synthetase in breast cancer : from molecular biology to clinical applications

Progesterone and estrogens play an important role in the control of growth, differentiation, and function of mammary epithelial cells. Their mechanism of action can be studied in human metastatic breast cancer cell lines (e.g., MCF7, T47D, and ZR75-1) that contain progesterone and estrogen receptors.2 We used this system to try to define progestin-regulated human genes that would permit study of progestin regulation of gene expression in cell culture and to develop clinical markers of progestin responsiveness. This paper summarizes our investigation of the progestin-regulated 250K protein, recently identified as human fatty acid synthetase (FAS).