Numerous studies have demonstrated that phospholipids and lysophospholipids act as lipid mitogens that affect cell proliferation and survival by altering various cell signaling pathways. Intracellular levels of phospholipids and lysophospholips are tightly regulated by their respective lipases and thus, the expression and activity of these enzymes is critical for cellular homeostasis. We have cloned a cDNA that encodes a novel putative lysophospohlipase. In view of its predicted molecular mass of 34 kDa, we have named it LPL34 (lysophospholipase 34). Our preliminary results indicate that the LPL34 mRNA is highly expressed in normal colon mucosa but absent or reduced in established colon cancer cell lines. Analysis of primary colon tumors and their matching normal tissues also revealed that the expression of LPL34 is absent or reduced in 4/4 tumor tissues. Consistent with these results, expression of exogenous LPL34 in cancer cells lacking endogenous LPL34 results in growth inhibition. We have proposed studies to further examine the role of LPL34 in digestive diseases such as colon cancer. We will analyze a larger pool of fresh-frozen and paraffin-embedded tissue specimens for the expression of LPL34 at both mRNA and protein levels. We will also investigate a correlation between LPL34 status and clinicopathological features. To investigate the molecular basis of LFL34-mediated growth suppression, we will study the effect of LPL34 on PI3-K/Akt and ERK-dependent mitogenic and survival signaling pathways. To determine whether lipase activity is critical LPL34-mediated growth suppressive effect, site-directed mutagenesis approach will be used to mutate the conserved lipase motif 'GHSMG' and effects of mutated LPL34 on cell growth and mitogenic signaling pathways will be investigated. These are exploratory /developmental studies that, upon conclusion, will provide us with sufficient new data and reagents that will form the basis of future in-depth studies investigating the molecular mechanism(s) of action of this novel lysophospholipase in general and its role in the digestive diseases in particular.
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