The biochemical mechanism by which epidermal growth factor (EGF) promotes corneal epithelial wound healing is unclear. the PI long-term goals are to investigate if phosphoinositides and their metabolic products play a role in wound-healing process of corneal epithelium. The hypothesis is that EGF-receptor interaction causes activation of phospholipase Cy1 (PLCy1), phospholipase D (PLD) and phosphatidylinositol 3-kinase (PI 3-kinase), each generating second messenger molecules that may participate in signal transduction pathways leading to increased DNA synthesis and mitosis during corneal epithelial wound-repair. The following findings in several cell types form the basis of our hypothesis: 1. EGF activates Pi 3-kinase, generating 3-phosphorylated phosphoinsotidies that may be important in cell growth and proliferation. 2. EGF stimulates PLCy1, hydrolyzing phosphatidylinositol 4,5-bisphosphate (PIP2) into myo-inositol trisphosphate (IP3) and diacylglycerol (DAG). both IP3, by mobilizing Ca2+, and DAG, by activating PKC, have been implicated in mitogenesis. 3. EGF causes several fold stimulation of PLD, producing phosphatidic acid (PA) with mitogenic properties.
The specific aims of this proposal fall into three research areas: 1. To investigate the effects of EGF on PI 3-kinase in corneal epithelial cells and determine whether changes in enzyme activity correlate with the rate of wound-repair. 2. To investigate the effects of EGF on PLCy1-mediated PIP2 hydrolysis in confluent and in actively proliferating corneal epithelial cells. Dose-response and time-course effects of EGF on PLCy1 and wound-repair will be determined. 3. To investigate the effects of EGF on PLD activity in corneal epithelial cells. A correlation between EGF-induced PLD activation and would repair will be determined. The effects of PlD, Pa and lysoPA on cell proliferation will also be investigated. The PI employs two model systems for our work on epithelial wound-repair: one, an in-vivo rabbit corneal epithelium model with chemical lesions, and the other, an in-vitro model using cultured corneal epithelial cells. The data obtained from these studies should provide useful information about the possible role of phospholipid derived second messengers in EGF-induced would-repair. The PI believe that these studies will contribute to better understanding of cellular signaling pathways that control cell growth and proliferation during corneal epithelial would healing.
|Akhtar, R A; Abdel-Latif, A A (1990) Specific binding of [3H]inositol 1,4,5-trisphosphate to bovine iris sphincter microsomal membranes. Curr Eye Res 9:387-92|