Role of Epimorphin and Progesterone in Breast Development

Institution: Lawrence Berkeley National Laboratory
Investigator(s): Jamie Bascom, Ph.D. -
Award Cycle: 2002 (Cycle VIII) Grant #: 8GB-0147 Award: $23,713
Award Type: Dissertation Award
Research Priorities
Biology of the Breast Cell>Biology of the Normal Breast: the starting point



Initial Award Abstract (2002)
The mammary gland is a specialized organ in mammals that undergoes distinct stages of development in order to perform a vital function for offspring; milk production. The epithelial cells, which produce milk, must receive proper signals from hormones in the blood, nearby cells and components of its microenvironment to acquire this function. Before epithelial cells can produce milk, they must develop into lobuloalveoli (functional units) through morphogenesis, a process that involves proliferation, invasion and structural changes. Breast cancer happens when signals for normal morphogenesis go awry, epithelial cells grow in a disorderly and uncontrolled manner. Epimorphin is a morphogenic signal that when overproduced in mice causes lobuloalveolar structures to develop prematurely and excessively.

By determining how microenvironmental signals like epimorphin control normal development, insight will be gained to the mechanisms that lead to abnormal signals that cause cancer. The specific type of morphogenesis that epimorphin plays a role in is the development of branched structures and of milk producing structures called lobuloalveoli. Progesterone, a hormone that circulates in the blood, binds to targets in epithelial and surrounding cells called progesterone receptors and also directs epithelial cells to branch and to develop into lobuloalveoli. I hypothesize that epimorphin and progesterone/progesterone receptor stimulate epithelial morphogenesis through a common pathway or through two separate pathways that collaborate in these developmental processes.

To determine if a relationship exists between epimorphin and progesterone/progesterone receptor in mammary morphogenesis, I will conduct experiments with mammary epithelial cells in culture and mammary glands in live mice. Quantification of these molecules will be done using standard molecular biology techniques. Mice that overproduce epimorphin in their mammary glands will be used along with normal mice to determine if progesterone receptor levels are increased by epimorphin. To determine if progesterone can regulate the production of epimorphin, I will treat epithelial cells that normally produce epimorphin with progesterone and determine if epimorphin levels increase compared to non-treated cells. I will also test whether progesterone treatments in ovariectomized mice increase the level of epimorphin.

To understand the anomalous behavior of breast cancer cells, the signals that cause deviations from normal developmental programs must be determined. Many of the inappropriate signals are the same ones that control normal development except that they are misregulated. This study will focus on the dynamic information that cause the specialized milk producing cells, the lobuloalveoli, to develop in the normal breast and how these same signals become disrupted in breast cancer.


Final Report (2003)
Epimorphin/syntaxin-2 (EPM) is a cell surface protein and acts as a “morphogen”: a molecule that controls normal structural development of many tissues including the mammary gland. When EPM is overproduced in the mammary glands of mice it leads to enlargened mammary ducts and disorganized alveolar structures during pregnancy[1]. Alveolar structures are the functional units of the mammary gland, in addition they are the primary source of breast cancers therefore alterations to their structure may play an important role in cancer progression. Progesterone, a steroid hormone critical for initiation and maintenance of pregnancy, has been found to induce mammary epithelial cells to undergo lateral branching morphogenesis and lobuloalveolar development [2-4]. The purpose of this fellowship was to determine when and where in the mammary gland is EPM expressed during the developmental cycle, to more completely characterize the EPM transgenic mouse phenotype, and to determine if there exists a relationship between EPM and progesterone signaling in the mouse mammary gland.

A closer examination of the EPM transgenic mouse has revealed that they have additional developmental abnormalities that arise during mammary ductal development at 8 weeks of age, after lactation when normally the milk producing alveolar structures die and milk production ceases, and in aged mice. We have found that EPM is most highly expressed during times of intense development of the mouse mammary gland occurring at puberty, pregnancy, and lactation. Surprisingly, we have found that the systemic hormones estrogen and progesterone negatively regulate EPM expression in mouse mammary gland. Further studies need to be performed to determine what stimulates EPM upregulation during mouse mammary gland development.

The role of EPM in normal breast development is relevant to the fight against breast cancer in light of several reports showing that other morphogens of the breast, that are similar in function to EPM, when deregulated, can lead to a breakdown of the tissue structure and stimulate tumor development and progression. Many of the morphogens known to stimulate breast development act as local mediators of systemic hormones such as estrogen and progesterone. By determining how systemic hormones control local morphogens of the breast, we will obtain a more complete understanding to how cancer is initiated and how it progresses.


Symposium Abstract (2003)
Epimorphin/syntaxin-2 (EPM) is a cell surface protein and acts as a ?morphogen?: a molecule that controls normal structural development of many organs and tissues including lung, hair follicle, gut, gallbladder, skin, liver, pancreas, and the mammary gland. When EPM is overproduced in the mammary glands of mice it leads to abnormalities in the ducts and the alveoli (Hirai et al., JCB 2001), structures that are the functional units of the mammary gland and that are the primary source of breast cancers. A closer examination of these mice has revealed that they have additional developmental abnormalities after lactation when normally the milk producing alveolar structures die and milk production ceases, while in EPM overproducing mice, this postlactational response is delayed. The role of EPM in normal breast development is relevant to the fight against breast cancer in light of several reports showing that other morphogens of the breast, that are similar in function to EPM, when deregulated, can lead to a breakdown of the tissue structure and stimulate tumor development and progression. Many of the morphogens known to stimulate breast development act as local mediators of systemic hormones such as estrogen and progesterone. By determining how systemic hormones control local morphogens of the breast, we will obtain a more complete understanding to how cancer is initiated and how it progresses. The goal of this proposal was to determine how EPM is regulated during the development of the breast and to examine a possible relationship between EPM and progesterone, a systemic hormone known to stimulate breast development that causes similar ductal abnormalities in mouse mammary glands when its target receptor is overproduced. We show here that EPM is most highly expressed during times of intense development of the mouse mammary gland occurring at puberty, pregnancy, lactation and during remodeling after lactation ceases. In addition, we show that the systemic hormones estrogen and progesterone negatively effect EPM expression in mouse mammary glands. These findings suggest that EPM is positively regulated during breast development by some factor(s) other than estrogen and progesterone. Further studies will be needed to determine what stimulates EPM upregulation during breast development, although a possible candidate is prolactin that also stimulates ductal/alveolar development and is expressed at similar stages of development to EPM.

This work was supported by grants from the US D.O.D. and the NCI to MJB. JLB and JEF are supported by fellowships from the CA BCRP (#8GB-0147 and #6FB-0131)