Mechanisms of Fluid Transport in Human Mammary Epithelium

Institution: University of California, Berkeley
Investigator(s): Sheldon Miller, Ph.D. -
Award Cycle: 1999 (Cycle V) Grant #: 5JB-0077 Award: $149,822
Award Type: IDEAS II
Research Priorities
Biology of the Breast Cell>Biology of the Normal Breast: the starting point



Initial Award Abstract (1999)
An abnormal accumulation of fluid occurs in the breasts of a large fraction of pre-menopausal women (>40%). This condition, termed gross cystic disease, is the most common benign disease of the breast and leads to an increased cancer risk 2- 4 times higher than the general population. This proposal aims to study a fundamental but little appreciated property of mammary epithelia - their ability to transport fluid and the relationship between fluid transport and the secretion of electrolytes and proteins that are commonly found in the cysts of patients with breast cystic disease. Mammary epithelia and epithelia throughout the body have the same general structure and function, they are sheets of tightly connected cells that either surround and protect the organs they serve or line the cavities of secretory glands. Epithelial cells have two functionally and structurally distinct surfaces termed apical and basolateral membranes. These two membranes face different extracellular environments on either side of the cell and contain different sets of proteins that permit the movement of nutrients, ions and fluid from one extracellular space to another. There is currently nothing known about the plasma membrane and signaling mechanisms that regulate the movement of fluid across mammary epithelia.

Fluid transport measurements will be carried out using a technique originally developed in this laboratory for work in eye and lung epithelia where issues of fluid transport are central to understanding disease (retinal detachments and cystic fibrosis, respectively). The research is risky since there is no clear cell or molecular basis for understanding the transition from breast cystic disease to hyperplasia to breast cancer. The completion of this work will provide two important benefits. First, we will have identified the transport proteins and signaling mechanisms that mediate the movement of fluid (and ions) across two kinds of intact epithelial monolayer cultures, one that emanates from "normal" (or fibrocystic) epithelia and the other from breast cancer epithelia. Secondly, based on this information we will be able to develop a pharmacological strategy for reducing fluid secretion or increasing fluid absorption across mammary epithelial cultures. This would provide the initial step toward a therapeutic intervention aimed at the reduction or elimination of the pathological accumulation of fluid secreted by epithelia in breast cystic disease. This kind of intervention may slow or reverse the development of breast hyperplasia. The benefits of preventing abnormal accumulations of fluid in gross cystic disease are three-fold: (1) a possible reduction in cancer risk or disease progression; (2) a reduction or removal of the considerable pain that inevitably accompanies the fluid-induced intracystic tension; (3) the removal of an impediment that continues to cause misdiagnosis of breast cancers by primary care physicians.


Final Report (2002)
A large fraction of pre-menopausal women suffer from an abnormal accumulation of fluid in their breasts. This condition, termed breast cystic disease (BCD), is the most common benign disease of the breast and leads to a significant increase in cancer risk.

The main goals of this research were two-fold: 1) to identify the transport proteins and intracellular signaling mechanisms that mediate the movement of fluid (and ions) across monolayer cultures of epithelia that emanate from "normal" (fibrocystic) and hyperplasic animal or human mammary epithelia; 2) develop a pharmacological strategy for reducing fluid secretion or increasing fluid absorption across these cultures.

We have identified several apical and basolateral membrane proteins and the intracellular signaling pathways that mediate the regulation of ion and fluid movement across intact epithelial sheets of cultured 31EG4 mouse mammary cells. We have found two types of chloride channels (CFTR, and calcium activated chloride channels), the amiloride sensitive sodium channel (ENaC), and potassium channels on the apical membrane. We have functionally identified P2Y-purinoceptors at both the apical and basolateral membranes, potassium channels at the apical membrane, and sodium/hydrogen (Na/H) exchangers at the basolateral membrane. The activities of these proteins work in concert to modulate the rate of fluid transport across this epithelium.

We have completed our functional analysis of the transport proteins in the mouse mammary 31EG4 cell line. Studies will continue beyond this funding to identify and functionally characterize the analogous ion and fluid transport mechanisms in primary human cell cultures of mammary epithelia. Our goal is to develop a pharmacological strategy for removing clinically significant amounts of breast fluid accumulation in BCD patients.

The information obtained during this project provides an initial step toward understanding how human mammary epithelia regulate fluid transport. Based on this work, and our work in other epithelial systems, such as eye and lung, we should ultimately be able to provide a therapeutic intervention strategy that can reduce or eliminate the pathological accumulation of fluid in BCD patients. The benefits of preventing abnormal accumulations of fluid in BCD are three-fold: (1) the removal of an impediment that continues to cause misdiagnosis of breast cancers by primary care physicians; (2) a reduction or removal of the considerable pain that inevitably accompanies the fluid-induced intracystic tension; (3) a possible reduction in cancer risk.

ENaC- and CFTR-dependent ion and fluid transport in mammary epithelia
Periodical:American journal of physiology. Cell physiology
Index Medicus: Am J Physiol Cell Physiol
Authors: Blaug S, Hybiske K, Cohn J, Firestone GL, Machen TE, Miller SS
Yr: 2001 Vol: 281 Nbr: 2 Abs: Pg:C633-48

P2 purinoceptors regulate calcium-activated chloride and fluid transport in 31EG4 mammary epithelia
Periodical:American journal of physiology. Cell physiology
Index Medicus: Am J Physiol Cell Physiol
Authors: Blaug S, Rymer J, Jalickee S, Miller SS
Yr: 2003 Vol: 284 Nbr: 4 Abs: Pg:C897-909