Secreted proteins involved in intercellular communications


Growth factors regulate proliferation and cellular activities that result in coordinated growth and differentiation of animal tissues. To achieve their effects, growth factors regulate gene expression and thus the production of new proteins. Proteins that are secreted are often involved in coordinating cell growth in multicellular tissues. Dr. Nilsen-Hamilton has discovered several secreted proteins that are regulated by growth factors. The research team is exploring the mechanisms by which the genes that encode these proteins are regulated and the functions of these proteins in controlling controlling cell functions.

The group discovered a unique fibroblast growth factor response element (FRE) in the mrp3 gene promoter. The FRE is also found in the promoters of many metalloproteinases that are important for cancer cell movement during metastasis. They have also found that the mrp/plf genes are expressed during wound healing and also in some fetal tissues. Mrp3 is the main Mrp/plf that is expressed in the wound.

Lipocalin 2 (Lcn2) is another secreted protein that is regulated by growth factors. It is an acute phase protein, produced by the liver, lungs and other epithelial tissues in response to stress such as occurs with infections.  The mouse protein is also called 24p3, SIP24, siderocalin, uterocalin, and the human protein is called NGAL. Lcn2 is also produced by the uterus around birth and in the mammary gland during involution after the young have stopped suckling. The protein is a lipocalin and may be involved in protection from infections by microbes during reproduction. A higher expression of this gene is also correlated with protection against breast cancer. The group is studying the protein’s function and how the gene is regulated.

To understand how growth-factor-induced genes are regulated and to identify the physiological functions of the protein products, Dr. Nilsen-Hamilton and her group are using biochemical, molecular, cellular, and developmental approaches, which have included purifying the proteins, cloning the genes, determining their sequences, identifying the relevant regulatory elements, and identifying new transcriptional regulators. They are using cell cultures to express the proteins and also as “reporter” systems to study the activity of the regulatory elements of each gene. Studies of the regulation of gene activity have also involved functional in vitro assays such as the electrophoretic mobility shift assay for transcription factors and in vivo studies of the levels of expression of the gene under different physiological conditions.

In fighting almost any disease the ability to detect and treat it in the early stages is critical to a successful outcome. For most diseases there are changes in gene expression and subsequent protein products that could be used for early detection. However, disease-initiated changes often occur in the depths of our tissues. Therefore a challenge for developing new technology to fight disease is to find ways of non-invasive imaging (e.g. no biopsy or surgery) of the body’s status. For example, the group is now using the Lcn2 promoter to drive expression of aptamer reporters that can be used to detect inflammation in transplanted tissues. This aptamer reporter technology is also being developed to monitor gene expression in models systems to gain insight into how cells communicate in their natural environments.