Growth Regulation in Breast Cancer

Godden, Judith Lilian (1992) Growth Regulation in Breast Cancer. PhD thesis, University of Glasgow.

Abstract

For the successful treatment of breast cancer it is important to understand the underlying mechanisms of growth regulation in breast tumours. This study has examined breast tumour cell growth at three different levels; growth factor regulation of cellular proliferation, growth factor effects on signal transduction pathways and fibroblast derived paracrine regulation of growth. Four different breast cancer cell lines were selected to cover a wide range of breast tumour characteristics. MCF-7WT and ZR-75-1 are two oestrogen and progesterone receptor positive cell lines which show oestrogen regulated growth, whilst MCF-7Adr and MDA-MB-231 are both oestrogen receptor (ER) negative but have increased levels of the epidermal growth factor receptor. Growth responses to oestradiol, the antiestrogen tamoxifen and a range of growth factors were examined in each of the cell lines using an MTT cell growth assay and cellular uptake of tritiated thymidine. Growth regulation by each of these factors was clearly seen in the two ER positive cell lines, although the effect was much smaller in the ZR-75-1 line. The ER negative cell lines produced no growth response to exogenously applied factors, although they did show a much higher level of growth in basal medium conditions. Given the importance of tyrosine kinase activity in signal transduction, patterns of tyrosine phosphorylation were compared in each of the cell lines when grown in low stimulatory growth conditions. It was interesting to note that overall tyrosine phosphorylation was much higher in the MCF-7Adr line than its parent MCF-7WT line, suggesting increased phosphorylation activity may partly explain why these cells have escaped external growth control. Evidence points to altered regulation of the ras GTPase activating (GAP) protein as one possible factor involved in the autonomous growth of the ER negative MCF-7Adr cell line. Tyrosine phosphorylation response to growth factor stimulation was also examined in the ER positive MCF-7WT and the ER negative MCF-7Adr cell lines. This generally resulted in phosphorylation of proteins specific to the growth factor, as well as phosphorylation of a number of substrate proteins which were common to each of the growth factors tested, suggesting different growth factors share the same signal transduction pathways. Finally, growth regulation of each of the breast cancer cell lines was examined within the broader context of a multicellular tumour environment. Fibroblast cell lines derived from breast tumour stromal tissue were examined for their capacity to regulate tumour cell growth through paracrine mechanisms. Breast cancer cell lines were exposed to conditioned medium from the fibroblasts and the growth response measured in an MTT assay. The two ER positive cell lines MCF-7WT and ZR-75-1 responded to fibroblast conditioned medium, again the affect was greater in the MCF-7WT line. The ER negative cell lines showing autonomous growth were unaffected by exposure to the conditioned medium. The conditioned medium was found to synergise with oestradiol to produce very large increases in the growth of MCF-7WT cells. This study suggests paracrine influences on tumour cell growth may be important in the progression of hormonally dependent breast tumours. In contrast, hormonally responsive or hormonally independent breast tumours show the capacity for self-regulated growth therefore appear to be less influenced by external factors. It is by defining the major growth influences affecting both hormone dependent and hormone independent tumours that new and important therapeutic targets will be identified.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: David Kerr
• Keywords: Oncology
• Date of Award: 1992
• Depositing User: Enlighten Team
• Unique ID: glathesis:1992-74807
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Sep 2019 16:05
• Last Modified: 27 Sep 2019 16:05
• URI: https://theses.gla.ac.uk/id/eprint/74807