Gene expression in oestrogen-dependent human breast cancer xenograft tumours

Abstract

Summary Xenograft tumours from an oestrogen-dependent human breast cancer cell line MCF-7 have been established and characterised in thymectomised, irradiated female CBA strain mice. There was evidence for selection in xenografts of a subpopulation of MCF-7 cells with an altered pattern of gene expression as measured by mRNA levels compared with the original cells in vitro. Tumorigenicity increased significantly on repeated animal passage but oestrogen dependence was retained. Following injection of the mice with oestrogen, mitosis was induced in the tumour cells with associated increases in thymidine uptake and percentage of cells in S-phase. In accord with these changes, c-myc and p53 expression were increased and TGF-beta was suppressed. Thereafter the expression of the c-myc and p53 genes fell whilst that of the TGF-beta gene was induced-as the oestrogenic stimulus declined. The oestrogen-regulated mRNA pS2 showed a biphasic response to oestrogen and levels declined as the serum oestrogen fell to undetectable levels. This xenograft system demonstrates that changes in transcription of oncogenes, growth factor and oestrogenregulated genes can be detected in vivo in response to oestrogen. It thus provides an in vivo model for studies of the biochemical and molecular basis for therapeutic manipulation of hormone-sensitive human breast cancer.In studying the molecular biology of cancer cells, the significance of in vitro observations may be uncertain due to the absence of host factors that influence tumour behaviour in vivo. Recent work on experimental human breast tumours in vivo has made use, almost exclusively, of congenitally athymic ('nude') mice Brunner et al., 1989). We have previously reported the growth of a range of human tumours in thymectomised, irradiated mice (Busuttil et al., 1986) which have advantages in ease of husbandry and cost (Steel et al., 1978;Morten et al., 1984;Hay et al., 1985). We report here the characterization of an oestrogenresponsive tumour derived from the MCF-7 human breast carcinoma cell line grown in vivo in female thymectomised and irradiated CBA mice. In addition, we have examined the kinetics of the expression of a range of related genes (c-myc, p53, TGF-beta and pS2) following oestrogenic stimulation in this tumour model system. Materials and methods Twenty

Involvement of Myc targets in c-myc and N-myc induced human tumors

“…The dierent patterns of expression exhibited by the various gene transcripts following the induction can be the result of dierence in their RNA stability in this system. It has been reported previously that ODC levels in MCF-7 cells are controlled by antiestrogens (Thomas et al, 1989) and that c-myc and p53 expression increase in these cells following estrogen treatment (Thompson et al, 1990). It is likely that the increased expression of the ECA39, Cdc25A, p53, ODC and a-prothymosin genes, seen in MCF-7 cells after 17b-estradiol treatment, is a result of their induction by c-Myc, which is induced by estrogen.…”

Allele loss from 5q21 (APC/MCC) and 18q21 (DCC) and DCC mRNA expression in breast cancer

“…It is possible that DCC expression may be increased in cells subjected to contact inhibition in keeping with its suggested function as a cell adhesion molecule . However, at the DNA and protein levels we have little idea of DCC function or expression in these xenografts which grow slowly and rarely metastasise (Thompson et al, 1990a). In addition, other mechanisms such as enhancer mediated silencing or gene methylation could account for DCC gene repression in vitro (Hohne et al, 1992).…”

“…In sporadic breast cancer, reports of LOH at the DCC locus range from only I of 40 (2.5%) informative cancers (Sato et al, 1991) to 13/45 (27%) tumours with DCC allele loss or duplication (Devilee et al, 1991). Less specific markers (OS4 at 18q21.3-qter) have shown 69% (11/34) allele loss (Cropp et al, 1990), 14% allele loss (Merlo et al, 1992), or 38% (17/45) allelic imbalance (Devilee et al, 1991) (Thompson et al, 1990a) were also snap frozen and stored at -70°C.…”

Induction of apoptosis in human lung cancer cells after wild-type p53 activation by methoxyestradiol

“…The total proteins were separated on 10% SDSpolyacrylamide gel and the p53 and actin proteins were detected by Western blot analysis using monoclonal antibodies as described earlier. (Thompson et al, 1990). Another study showed that pretreatment with 17 b-estradiol protected MCF-7 cells from apoptosis by increasing the production of bcl-2, an anti-apoptotic protein (Wang et al, 1995).…”