Research in the Cohick laboratory focuses on the role of the insulin-like growth factor (IGF) system in normal mammary gland physiology as well as breast cancer. The IGFs are peptide growth factors that regulate cell proliferation, differentiation, survival and migration, processes critical to both normal mammary gland development and lactation as well as breast cancer tumorigenesis. They associate with a family of high affinity binding proteins (IGFBPs) that function to transport the IGFs in the circulation and prolong their half-life. In addition, IGFBPs act at the cellular level to either enhance or inhibit the biological actions of IGFs as well as many other agents that affect cell growth, survival and migration. It is now generally accepted that many of these effects are independent of binding to IGF, although the precise mechanisms are generally unknown.

Specific research areas:

1. Molecular regulation of IGFBP-3 synthesis:
   We have found that both IGF-I and epidermal growth factor (EGF; another peptide growth factor that stimulates cell growth) are positive regulators of IGFBP-3 synthesis. Paradoxically, we have also found that several growth inhibitory agents also induce IGFBP-3 synthesis in these cells. Studies are ongoing to determine the molecular mechanisms by which both growth-stimulatory and growth-inhibitory agents regulate IGFBP-3 synthesis in the same cell system. Currently, we have shown that both IGF-I and the protein synthesis inhibitor anisomycin stabilize IGFBP-3 mRNA, leading to an increase in IGFBP-3 protein levels. We have also determined the intracellular signaling cascades that each of these factors activate, and which of these pathways are required for IGFBP-3 synthesis. Studies are in progress to determine how these signaling pathways regulate IGFBP-3 mRNA stability in response to either IGF-I or anisomycin.
2. Physiological role of IGFBP-3 in mediating mammary epithelial cell growth.
   1. At the cellular level, IGFBP-3 may either inhibit or enhance cell proliferation on its own, or alter the effectiveness of other growth-regulatory agents. Several laboratories, including our own, have shown that it does this by either directly or indirectly altering the activation of intracellular signaling cascades in mammary epithelial cells or breast cancer cells. We have shown that mammary epithelial cells genetically modified to overexpress IGFBP-3 are more responsive to IGF-I in terms of DNA synthesis (see Figure 1). This is due to enhanced activation of the phosphatidyl-inositol 3 kinase intracellular signaling pathway in response to IGF-I (see Figure 2). It is presently unknown if this response is initiated at the cellular membrane or within the cell. The specific mechanism by which this occurs is presently being investigated.
      
      

      Figure 1	Figure 2

   2. We are also interested in the seemingly contradictory role of IGFBP-3 in mediating the action of both growth-stimulatory and inhibitory agents, which fits with the ability of both to increase its synthesis. We are presently using genetic methods such as small interfering RNA (siRNA) as well as genetically modified animals to determine if the ability of IGF-I and anisomycin to regulate cell growth and apoptosis (programmed cell death), respectively, will be altered in the absence of IGFBP-3.
      
      Additional areas of interest include determining the role of IGFBP-5 in regulating growth, differentiation, and apoptosis of mammary epithelial cells, and the role of extracellular matrix and growth factor interactions in mammary cell growth.
3. Mechanism of action of ricin in mammalian cells:
   
   Ricin is a ribosome inactivating protein that represents a potential agent of biological warfare. In collaboration with Dr. Nilgun Tumer, a plant virologist and molecular biologist in the Biotech Center, we are studying the mechanism by which this plant toxin kills mammalian cells.
4. Role of estrogen in breast cancer susceptibility:
   
   Considerable epidemiological data indicates that increased life-time exposure to estrogen increases a women’s risk of breast cancer. However, the exact mechanisms by which this occurs are controversial and not well-established. Working with researchers in the Environmental Occupational Health Sciences Institute at Rutgers, we are using the ACI rat model to study the role of estrogen in breast cancer susceptibility to environmental carcinogens and other factors that may promote cancer. This animal develops mammary tumors in a predictable fashion when exposed to estrogen.

Selected Recent Publications:

Fleming JM, Leibowitz BJ, Kerr DE, Cohick WS. 2005 IGF-I differentially regulates IGF binding protein expression in primary mammary fibroblasts and epithelial cells. J Endocrinol 186:165-178.

Sivaprasad U, Fleming J, Verma PS, Hogan KA, Desury G, Cohick WS. 2004 Stimulation of insulin-like growth factor (IGF) binding protein-3 synthesis by IGF-I and transforming growth factor-α is mediated by both phosphatidylinositol-3 kinase and mitogen-activated protein kinase pathways in mammary epithelial cells. Endocrinology 145:4213-4221.

Cornwell T, Cohick WS, Raskin I. 2004 Dietary phytoestrogens and health. Phytochemistry 65:995-1016.

Grill CJ, Sivaprasad U, Cohick WS. 2002 Constitutive expression of IGF binding protein-3 by mammary epithelial cells alters signaling through akt and p70S6 kinase. J Mol Endocrinol 29:153-162.

Grill CJ, Cohick WS, Sherman A. 2001 Postnatal development of the rat mammary gland is preserved during iron deficiency. J Nutrition 131:1444-1448

Cohick WS, Wang B, Verma P, Boisclair Y. 2000. Insulin-like growth factor-I and cyclic AMP regulate IGF binding protein-3 gene expression by transcriptional and post-transcriptional mechanisms in mammary epithelial cells. Endocrinology 4583-4591.

Grill CJ, Cohick WS. 2000. Insulin-like growth factor binding protein-3 mediates IGF-I action in a bovine mammary epithelial cell line independent of an IGF interaction. J Cellular Physiology 183:273-283