Identification of novel gene, TRAP1, using a replication-competent promoter-trap retrovirus in the mouse mammary gland.

Breast cancer remains one of the leading malignancies in women of the developed world despite the extra efforts that have been deployed in the past decade or so to the study of this disease. It is well known that the degree of aggressivity of the tumor is related to the stage of differentiation. Transformation of a cell having a high proliferation potential will lead to a more aggressive tumor than transformation of a more differentiated cell. For this reason it is important to have a good understanding of the process of mammary differentiation. The work in this thesis was directed at finding novel genes that are involved in the normal development of the breast with the hope that these may open new avenues for breast cancer therapies. The approach used was to look for genes that are expressed during breast development in the living mouse. A promoter-trap retrovirus containing on oncogene as the promoterless indicator gene was introduced locally in the mammary glands of pubescent female mice. Integration of proviruses near an active cellular promoter lead to the expression of the oncogene from a cellular promoter which was detected by the formation of a tumor. To identify genes that are specifically active during differentiation of the breast tissue we looked for the appearance of tumors after the animals were mated. Two promoter-trap retroviruses were tested. The first one (COPT) was replication deficient and although it did work in vitro it did not give a high enough level of infection to be used in vivo. The second virus (PyT) was replication competent and was found to be a more suitable promoter-trap to be used in vivo. This was demonstrated by the isolation of a novel murine gene named TRAP1