The Invasive Nature of Epithelial Breast Cancer Cells

Institution: Lawrence Berkeley National Laboratory
Investigator(s): Pierre-Yves Desprez, Ph.D. - Pierre-Yves Desprez, Ph.D. -
Award Cycle: 1995 (Cycle I) Grant #: 1KB-0274 Award: $105,837
Award Type: New Investigator Awards
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

This is a collaboration with: 1KB-0274A -

Initial Award Abstract (1995)
Growth and differentiation (transition from one function to another) are intimately connected and controlled in normal cells. Cancer cells differ from normal in at least three fundamental ways. First, cancer cells grow inappropriately. Second, they become aberrantly differentiated. These two features are fundamental to virtually all cancers, and are inseparable. Cancer cells may also leave the body site from which they originated, invade the surrounding tissue and grow in otherwise foreign sites. This research will provide critical insights into how cancer cells lose proper control over growth and differentiation. We developed a cell culture system of mammary epithelial cells, the cells from which 90% of all breast cancers arise. We found that an extracellular matrix (ECM, an interwoven network of proteins that give strength and support to cells) in contact with the cells is critical for inducing normal growth cessation and differentiation. We also found that an intracellular protein known as Id-1 is critical for coordinating the changes in growth and differentiation induced by the ECM. In the mammary gland and in culture, Id-1 is produced when cells are growing, but not when they are growth arrested. We created breast epithelial cells in which Id-1 is always present. When contacted by ECM, these perpetual Id-1-expressing cells failed to undergo the change in differentiation, and migrated from their original site, grew and invaded the surrounding ECM.

How does Id-1 do this, and can we reverse the effect of Id-1 and induce abnormal cells to behave more normally? We know that Id proteins act by binding and inactivating another class of proteins called bHLH transcription factors. We hypothesize that normal breast epithelial cells produce bHLH proteins, which are essential for the cells to arrest growth, differentiate, and remain non-invasive. We will introduce the identified bHLH genes into undifferentiated breast cancer cells and ask whether the cells can now be induced to cease growth and differentiate. We will introduce these genes into metastatic cells and ask whether the cells lose the ability to invade surrounding tissue and colonize foreign sites. We will also test the effects of anticancer agents such as vitamin D3 and ask whether they act by reducing Id-1 expression. We propose that master genes like those encoding bHLH or Id proteins can alter the pattern of genes expressed by breast cancer cells, and thus alter their growth, differentiation and invasiveness.

Final Report (1998)
Cancer cells differ from normal cells in several ways. Cancer cells grow inappropriately, they do not become specialized they should, and they may leave the body site from which they originated, invade the surrounding tissue and grow in other parts of the body. This research will provide critical insights into how cancer cells lose proper control over growth, differentiation and invasion. We have shown that the expression of an intracellular protein, known as Id-l, correlates with the growth state of the cells, and that this protein is down regulated during the gain of function (milk production). In addition, we created murine mammary epithelial cells in which Id-l was always present. We found that these cells were unable to produce milk and, more importantly, the cells expressed an enzyme (gelatinase) and acquired the ability to invade the surrounding microenvironment. By contrast, control cells did not have the above characteristics. We therefore suggested that Id- l could be an important protein whose altered regulation in mammary cells results in a proliferative and invasive potential in breast cancer.

In order to investigate our hypothesis, we examined Id-l expression level in different types of human breast cancer cell lines (a total of nine cell lines has been investigated). Under serum-free culture condition, Id- l protein was found to be constitutively expressed at high levels in the most invasive tumor cell lines (called MDA-MB-23 l, MDA-MB436 and MDA-MB435), and at an intermediate level in another invasive cell line (called Hs578T). Meanwhile, Id-l was expressed at very low levels in less aggressive and non-invasive breast tumor cell lines (called T47D, MCF-7, ZR75-l and SKBR-3). An exception was the invasive BT549 cells which did not express any detectable Id-l. Lake murine epithelial cells which always produce Id-l, MDAMB-23 l, MDA-MB-436, MDA-MB435, and at a lower extent Hs578T cells, also expressed a gelatinase of the same size, whereas the non-invasive T47D, MCF-7, ZR75-1 and SKBR-3 cells did not express it. As sex steroid hormones are known to be important regulators of breast cancer progression and treatment, we also examined the possible connection between the hormones and Id- l expression. We found that estrogen treatment upregulated Id- l expression in T47D cells and that co-treatment of estrogen and progesterone downregulated Id-l expression and inhibited growth in the same cells. More strikingly, we have evidence that Id-l can mediate the effect of the two hormones on the proliferation of breast cancer cells positive for the hormone receptors. When T47D cells were treated with estrogen and Id-l artificially maintained at a low level of expression, cell proliferation was reduced in comparison with treatment of estrogen alone. Meanwhile, T47D cells with constitutive Id-l expression were no longer able to respond to progesterone treatment, and they maintained a relatively high growth rate independent of serum in the culture medium. This might provide important molecular mechanisms for some of previously known hormone actions in treatment of breast cancer, and we propose that Id-l protein is a potential candidate for master regulator of aggressiveness and invasiveness in breast cancer.