UVM Theses and Dissertations
Format:
Print
Author:
Zhong, Yili
Dept./Program:
Animal Sciences
Year:
2010
Degree:
MS
Abstract:
The mammary gland growth and differentiation is regulated by both systemic hormone and locally produced growth factors. Among these important hormones and growth factors, estrogen plays a central and essential role in mammary gland development. The biological function of estrogen is mediated by estrogen receptors. There are two types of estrogen receptors, ER[alpa] and ER[beta]. They share large similarity in structure and both receptors can bind to estrogen responsive element sequences in the promoter region of corresponding genes. Although both receptors bind to estrogen with similar affinity and both receptors can bind to estrogen responsive element sequences, studies on human and rodent estrogen receptors indicate that ER[beta] may have quite different function from that of ER[alpa] in regulating mammary epithelial cell proliferation and differentiation. ER[alpa] has been implicated in mediating the mitogenic function of estrogen.
The role of ER[beta] in mammary epithelial cell proliferation remains controversial. Studies using human breast cancer cell lines suggest that ER[beta] may function as a tumor suppressor to inhibit cell proliferation. In the in vivo mouse studies, however, activation of ER[beta] with ER[beta] specific agonist was shown to promote cell proliferation of normal mammary epithelial cells. In this study, we evaluated the effect of bovine ER[alpha] and ER[beta] on cell proliferation using the immortalized normal bovine mammary epithelial cell line Mac-T cells. Mac-T cells are negative for both ERs and the expression of ERs was restored by transient infection using ER[alpha] or ER[beta] expressing lentiviruses. Similar to the estrogen receptors in other mammalian species, both bovine ER[alpha] and ER[beta] are localized in the nucleus and can bind to the ERE sequences to stimulate the expression of reporter genes. In Mac-T cells overexpressing bovine ERalpha], we did not observe significant effect on cell proliferation suggesting that ER[alpha] is not sufficient to promote Mac-T cell proliferation under the culture condition in this study. in mammary epithelial cell proliferation remains controversial. Studies using human breast cancer cell lines suggest that ER[beta] may function as a tumor suppressor to inhibit cell proliferation. In the in vivo mouse studies, however, activation of ER[beta] with ER[beta] specific agonist was shown to promote cell proliferation of normal mammary epithelial cells. In this study, we evaluated the effect of bovine ER[alpha] and ER[beta] on cell proliferation using the immortalized normal bovine mammary epithelial cell line Mac-T cells. Mac-T cells are negative for both ERs and the expression of ERs was restored by transient infection using ER[alpha] or ER[beta] expressing lentiviruses. Similar to the estrogen receptors in other mammalian species, both bovine ER[alpha] and ER[beta] are localized in the nucleus and can bind to the ERE sequences to stimulate the expression of reporter genes. In Mac-T cells overexpressing bovine ER[alpha], we did not observe significant effect on cell proliferation suggesting that ER[alpha] is not sufficient to promote Mac-T cell proliferation under the culture condition in this study.
In Mac-T cells overexpressing bovine ER[beta], we found that cell proliferation was significantly inhibited. FACS analysis on cell cycle distribution showed that more cells were in the G2/M phase, suggesting that bovine ER[beta] may induce G2/M arrest in Mac-T cells. Moreover, the inhibitory function of bovine ER[beta] is independent of estrogen binding. In summary, our data support that ER[beta] is a negative regulator of mammary epithelial cell proliferation and the inhibitory effect of ER[beta] is conserved across mammalian species. The inhibitory function of ER[beta] may partly be mediated by causing cell cycle arrest at G2/M phase. Bovine ER[beta] is highly expressed during late lactation and involution stages, stages with extensive apoptosis. The inhibitory role of ER[beta] suggests that ER[beta] may be involved in inducing apoptosis during these stages.
The role of ER[beta] in mammary epithelial cell proliferation remains controversial. Studies using human breast cancer cell lines suggest that ER[beta] may function as a tumor suppressor to inhibit cell proliferation. In the in vivo mouse studies, however, activation of ER[beta] with ER[beta] specific agonist was shown to promote cell proliferation of normal mammary epithelial cells. In this study, we evaluated the effect of bovine ER[alpha] and ER[beta] on cell proliferation using the immortalized normal bovine mammary epithelial cell line Mac-T cells. Mac-T cells are negative for both ERs and the expression of ERs was restored by transient infection using ER[alpha] or ER[beta] expressing lentiviruses. Similar to the estrogen receptors in other mammalian species, both bovine ER[alpha] and ER[beta] are localized in the nucleus and can bind to the ERE sequences to stimulate the expression of reporter genes. In Mac-T cells overexpressing bovine ERalpha], we did not observe significant effect on cell proliferation suggesting that ER[alpha] is not sufficient to promote Mac-T cell proliferation under the culture condition in this study. in mammary epithelial cell proliferation remains controversial. Studies using human breast cancer cell lines suggest that ER[beta] may function as a tumor suppressor to inhibit cell proliferation. In the in vivo mouse studies, however, activation of ER[beta] with ER[beta] specific agonist was shown to promote cell proliferation of normal mammary epithelial cells. In this study, we evaluated the effect of bovine ER[alpha] and ER[beta] on cell proliferation using the immortalized normal bovine mammary epithelial cell line Mac-T cells. Mac-T cells are negative for both ERs and the expression of ERs was restored by transient infection using ER[alpha] or ER[beta] expressing lentiviruses. Similar to the estrogen receptors in other mammalian species, both bovine ER[alpha] and ER[beta] are localized in the nucleus and can bind to the ERE sequences to stimulate the expression of reporter genes. In Mac-T cells overexpressing bovine ER[alpha], we did not observe significant effect on cell proliferation suggesting that ER[alpha] is not sufficient to promote Mac-T cell proliferation under the culture condition in this study.
In Mac-T cells overexpressing bovine ER[beta], we found that cell proliferation was significantly inhibited. FACS analysis on cell cycle distribution showed that more cells were in the G2/M phase, suggesting that bovine ER[beta] may induce G2/M arrest in Mac-T cells. Moreover, the inhibitory function of bovine ER[beta] is independent of estrogen binding. In summary, our data support that ER[beta] is a negative regulator of mammary epithelial cell proliferation and the inhibitory effect of ER[beta] is conserved across mammalian species. The inhibitory function of ER[beta] may partly be mediated by causing cell cycle arrest at G2/M phase. Bovine ER[beta] is highly expressed during late lactation and involution stages, stages with extensive apoptosis. The inhibitory role of ER[beta] suggests that ER[beta] may be involved in inducing apoptosis during these stages.