Targeting of Phosphoinositide Signaling in Cell Migration and Tumor Progression

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DESCRIPTION (provided by applicant): Tumor metastasis is responsible for most treatment failures in breast cancer patients. In cancers of epithelial origin, loss of epithelial cell polarity and transformation into a migratory phenotype are key steps in invasion of cancer cells. Intravasation of cancer cells appears to be dependent upon epidermal growth factor (EGF)-stimulated chemotaxis. Chemotaxis and invasion depends upon dynamic adhesion to extracellular matrix and actin cytoskeleton remodeling. Phosphoinositide signaling plays a key role in these processes, but the underlying mechanisms are poorly defined. Type Igamma phosphatidylinositol-4-phosphate 5-kinase (PIPKIgamma) synthesizes phosphatidylinositol-4,5- bisphosphate (PIP2) in a temporal and spatial fashion within cells. Hypothesis: PIPKIgamma isoforms, via their expression, targeting, and regulation by EGF-stimulation, generate the messenger PIP2, which modulate the spatial and temporal assembly of focal adhesions and vesicular trafficking that regulates chemotaxis. The role of PIPKIgamma in regulating migration is key in the metastasis of tumors. Specific Aims: (1) The mechanistic role of PIPKIgamma in growth factor-stimulated directional migration and invasion will be investigated. EGF signaling mechanisms leading to phosphorylation of PIPKIgamma will be characterized as will the role of PIP2 production in regulating tyrosine phosphorylation of PIPKIgamma and other proteins at focal adhesions. The underlying mechanism for PIPKgamma participation in EGF- stimulated chemotaxis and invasion will be explored, with an emphasis on the dynamic assembly of focal adhesions (FA) and vesicular trafficking. GFP/RFP-focal adhesion proteins will be used to define the role of PIPKIgamma in focal adhesions dynamics in EGF-stimulated cells. (2) Two new alternatively spliced PIPKIgamma isoforms that express unique C-terminal extensions will be characterized. PIPKIgamma splice variants interacting partners, intracellular targeting, and regulation will be defined. The roles played by these PIPKIgamma isoforms in cell migration will be investigated. (3) The role of PIPKIgamma splice isoforms in breast cancer intravasation and metastasis will be defined using a mouse model. (4) Changes in PIPKIgamma content and isoform expression in breast tumors will be studied using a large and well characterized breast tumor tissue microarray. We will investigate changes in PIPKIgamma expression levels in breast tumors and correlate this with other signaling molecules and biomarkers and with patient outcomes. This Aim will be the beginning of a long-term study to relate changes in PIPKIgamma expression with tumors of epithelial origin. This approach may yield important information, which will help to define the underlying mechanisms for our cell and molecular biology studies. In addition, our mechanistic studies will be translated into a greater understanding of breast cancer cell invasiveness.