Dr. John P. Wiebe
Hormonal Regulatory Mechanisms
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Position: Professor Office: BGS 3030
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Summary of Current Work
Role of progesterone metabolites in breast cancer
For the majority of breast cancers there has been no adequate hormone-based explanation and therapy. The only hormone-based therapies for breast cancer involve suppressing the body’s estrogen levels and actions. Unfortunately , these therapies are effective in only a portion ( about 1/3) of breast cancer patients and only for a limited time. We have identified two new types of steroid hormones, produced in breast tissue from progesterone (progesterone metabolites), that appear to have the ability to regulate all forms of breast cancer. One hormone, 5a-pregnane-3,20-dione (5aP), is cancer-promoting, since it stimulates cells to proliferate (tumor growth) and to detach (metastasis). The other hormone, 3a-hydroxy-4-pregnen-20-one (3aHP), is cancer-inhibiting since it suppresses cell proliferation and detachment. Our in vitro studies, conducted on 5 different human breast cell lines, have shown that both 5aP and 3aHP act on estrogen-responsive and estrogen non-responsive cells, as well as on tumorigenic and non-tumorigenic cells. The results strongly suggest that 5aP and 3aHP may have the capacity to regulate all forms of breast cancer, the final result depending on the ratio of the two hormones in the breast tissue microenvironment. New detection assays and new hormone-based treatment for breast cancer are suggested by our findings.
Our findings to date
- Tumor tissue and tumorigenic cells produce significantly higher levels of 5aP and lower levels of 3aHP than normal tissue and non-tumorigenic cells.
- The shift to tumorigenicity is accompanied by significant increases in activity and mRNA expression of the enzyme (5a-reductase) catalyzing conversion to 5aP and decreases of the enzyme (3a-hydroxysteroid oxidoreductase; 3a-HSO) catalyzing conversion to 3aHP.
- 5aP results in significant increases in proliferation and detachment, whereas 3aHP inhibits proliferation and detachment in all breast cell lines studied to date.
- Blocking the action of 5a-reductase with the inhibitor dutasteride blocks the production of 5aP and the resultant increases in proliferation and detachment.
- Novel, separate and distinct receptors for 5aP and 3aHP are located in the cell membranes. The binding of either 5aP or 3aHP to the respective binding sites occurs with high affinity and specificity; the ligands are not displaced by each other nor by other progesterone metabolites, estradiol, progesterone, androgens, or corticosteroids. Levels of 5aP receptors are up-regulated by estradiol and 5aP and down-regulated by 3aHP (and 20aHP).
- 5aP exhibits marked effects on the F-actin cytoskeleton and on vinculin-associated adhesion plaques.
- The actions of 5aP appear to involve the mitogen activated protein kinase (MAPK) signaling pathway, by way of the membrane-located receptors.
We propose to determine if 5aP and 3aHP actually regulate induction, growth and regression of mammary tumors by testing the effects of the hormones in vivo (in a living organism).
Hypothesis. The hypothesis is that 5aP will stimulate cells injected into mice in the same way that it stimulates cells in culture dishes, resulting in formation, growth and metastasis of tumors; conversely, blocking 5aP formation (with the inhibitor, dutasteride) and/or treatment with 3aHP will suppress tumor formation, growth and metastasis and/or cause regression of established tumors.
Current grant funded research objectives
- To determine what factors in the body (particularly in the breast tissue) cause the changes in progesterone metabolizing enzyme expression and activity that lead to higher 5aP and lower 3aHP production and tumor development.
- To determine the in vivo effects of the progesterone metabolites on induction, growth and regression on mammary tumors.
- To identify the molecular structures of 5aP and 3aHP membrane receptors.
- To identify cellular and molecular mechanisms and cell signaling pathways of 5aP and 3aHP actions.
