Research Grants Awarded
A role for Pnck as a sensitizer to breast cancer therapeutics.
Tumor Cell Biology VI
Although much understanding of breast cancer has been gained by research generated in the past two decades, many of the molecular players involved in this disease have only recently been discovered. The current proposal addresses the role of a recently identified protein expressed in human breast cancer, a novel kinase, termed Pregnancy Up-regulated Non-ubiquitous CaM kinase (Pnck). Pnck is a Ca/calmodulin dependent serine/threonine protein kinase that is highly expressed in primary human breast cancer, but not in adjacent benign tissues. Differential expression and/or activation of a protein in cancer cells but not in benign cells, is a potentially attractive target for translational cancer research. We have recently discovered that Pnck induces epidermal growth factor receptor (EGFR) degradation in a ligand-independent manner. The mechanism of ligand-independent EGFR degradation is poorly understood, compared to the mechanism of ligand-dependent EGFR degradation. EGFR is over expressed in a variety of cancers, including breast cancer, and its degradation by Pnck, makes Pnck a research target with a potentially high therapeutic value. Depletion of Pnck protein by siRNA resulted in up regulation of EGFR expression in human breast cancer cells, thereby independently validating Pnck function. Further research revealed that a number of proteins in addition to EGFR, namely HER-2/ErbB2, Akt, ER-á, HIF-1á, MEK-1 are also downregulated, presumably by degradation, in Pnck-overexpressing cells. The correlation between all of these diverse proteins is that they are all clients of heat shock protein 90 (Hsp90), and each of them could be tumorigenic in progression of normal breast cells to breast cancer. We hypothesized that Pnck itself is an endogenous Hsp90 protein inhibitor, as we have shown that Pnck sensitizes cells to the pharmacologic effects of the Hsp90 inhibitor, geldanamycin, which is currently under phase II clinical trial. Biochemical studies revealed that Pnck forms a complex with Hsp90, thus potentially inhibits Hsp90?s client stabilizing function, resulting in degradation of client proteins. Pnck?s over expression in breast cancer, and subsequent inhibition of Hsp90 make Pnck as an ideal sensitizer for Hsp90-based and Hsp90 client-based therapeutics. This study thus proposes a role for Pnck as a sensitizer to breast cancer therapeutics, which are either currently in use or under clinical trials. In aim 1, we will examine Pnck?s role as a sensitizer to breast cancer therapeutics in inducibly over expressed breast cancer cells, in vitro. In Aim 2, we will study the role of Pnck as sensitizer to breast cancer therapeutics in inhibiting breast tumorigenesis using animal xenograft breast cancer model. We propose that Pnck has potential tumor suppressive functions that can be used as a biomarker for future breast cancer therapy.
Breast cancer arises through a series of changes in a cell, driving normal healthy breast cells to grow inappropriately. When a normal protein(s) is over expressed or its mutated version is expressed in a differential/inappropriate time or place, the function of the protein is no longer normal and may contribute to the metamorphous of a normal cell to cancer cell. Parallel to this pro-cancer process, breast cells also express a number of proteins, called tumor suppressors, which oppose cancer development. Pregnancy-Upregulated Non-ubiquitous CaM Kinase (Pnck) is one such protein, which possesses a probable anti-cancer role. It is expressed in the mouse breast during late stages of pregnancy, a time characterized by decreased mammary epithelial cell proliferation. Pnck is also present at 3-5 fold greater levels in primary human breast cancer in comparison to the benign tissues adjoining the breast tumor. However, the physiological function of Pnck was not known until our recent discovery showed that Pnck degrades a growth factor receptor, called epidermal growth factor receptor (EGFR). EGFR is over expressed in breast cancers and transduces extracellular or external growth signals for cancer development to the interior of a cancer cells. Subsequently, we discovered that other proteins, which are over expressed and contribute to breast cancer development, are also down regulated or degraded by Pnck. Chemotherapeutics, and other breast cancer therapies, are currently used to down regulate/degrade or inactivate these proteins. Thus, we have identified a protein (Pnck) inside the breast cancer cells with equivalent functions of breast cancer therapeutics. Our investigation further revealed that Pnck inhibits the function of a central protein, called heat shock protein 90 (Hsp90), which functions to stabilize many cancer promoting proteins. Pnck?s inhibition of Hsp90 thereby results in the degradation of the pro-cancerous proteins that were stabilized by Hsp90. A drug that inhibits Hsp90 is currently under phase II clinical trial and we have observed that Pnck can sensitize its functions. This study thus proposes Pnck as a sensitizer to breast cancer therapeutics, currently being used or under clinical trials. Since a screen of 24 human breast tumor samples revealed that at least 30% express Pnck, we propose that considering Pnck as an internal therapeutic or biomarker will effectively reduce the dose and side effects arising from todays breast cancer treatment. In this application, Pnck?s efficiency in sensitizing the breast cancer therapeutics thus increasing their efficacy will be examined by human breast cancer cell and animal models.