Breast cancer can result from excessive proliferation and/or insufficient apoptosis of mammary epithelium. During a woman's life, the breast undergoes dramatic developmental changes with associated changes in proliferation and apoptosis. Reproductive factors associated with increased ovarian hormone exposure, e.g. early menarche and late menopause, increase breast cancer risk. Conversely, factors such as late menarche, early pregnancy and oophorectomy decrease that risk. Not all women become pregnant nor is it likely that early pregnancy or oophorectomy will become generally recommended to decrease breast cancer. In contrast, virtually all women menstruate and, during each menstrual cycle, their mammary epithelium undergoes proliferation, differentiation and apoptosis. If proliferation and apoptosis are not well balanced during the menstrual cycle, these cyclic changes may result in mammary hyperplasia and an increased risk for breast cancer. This is the context in which we propose to study the role of AICt 1 in mammary gland development. Akt I activation is common to hormone, growth factor and anchorage mediated epithelial cell survival and Ha-rasinduced tumorigenesis. Akt I has been shown to inhibit apoptosis induced by hormone or growth factor withdrawal and loss of anchorage. Thus, expression and activation of Akt 1 is shared by a number of pathways important for cell survival, and may link very different paths to breast cancer. We found decreased Akt 1 activation in the mammary gland during involution and the estrus cycle during periods of apoptosis. Akt 1 expression and activation peaks in lactation, then decreases during the period of epithelial cell apoptosis m involution. A similar pattern is found in the mammary gland during the estrus cycle, Akt- 1 activation is strong during proestrus and estrus, and is strongly decreased during metestrus and recovers in diestrus. This pattern is consistent with a role in modulating cell survival and it led us to examine Akt 1 expression in mammary hyperplasias and tumors. AIct 1 expression and activation was increased in three different lines of hyperplasia and was strongly increased in tumors with very different etiologies. These data support the hypothesis that increased expression or activation of Aki 1 is able to alter the survival of mammary epithelial cells by inhibiting apoptosis and thus, contributes to mammary tumorigenesis. Furthermore, these data suggest that inhibition of Akt activation in mammary hyperplasia may impede mammary carcinogenesis. We propose to examine these hypotheses by: 1) irnmunoblot and immunobistochemical analyses of Akt 1 activation and signaling pathways effected in the mammary gland during involution and the estrus cycle; studying the role of hormone milieu in regulation of expression and activation of Akt 1 in mammary cell cultures and inhibiting Aict activation in breast cancer cells; 2) examining the role of activated AIct 1 in mammary epithelial cell survival during the estrus cycle and it's potential contribution to mammary hyperplasia usmg myr-Akt 1 transgenic mice; and 3) studying the potential for inhibiting tumorigenesis in high risk mammary hyperplasia cells by expressing a dominant negative Akt i in mammary fat pad implants of TM-4 hyperplasia cells.
| Strange, R; Westerlind, K C; Ziemiecki, A et al. (2007) Proliferation and apoptosis in mammary epithelium during the rat oestrous cycle. Acta Physiol (Oxf) 190:137-49 |
