Pancreatic cancer is the fourth leading cause of cancer-related death in the United States. Strong basic research efforts are urgently needed to understand the molecular mechanisms responsible for its aggressiveness and to design novel anti-cancer therapies. Recent studies suggest that, besides their physiological role, mucins play a part in the pathogenesis of cancer: mucin1 (MUC1) overexpression has been observed in various cancers, including pancreatic cancer. It is believed that the carboxy terminal peptide of MUC1 is targeted to the mitochondria and inhibits apoptosis by preventing the release of cytochrome c (Cyt C). However, the mechanism by which MUC1 translocates to the mitochondria is unclear, since MUC1 lacks any mitochondrial localization sequence. It has been suggested that Heat Shock Proteins (HSPs) may participate in the mitochondrial translocation of MUC1, and studies in our laboratory have demonstrated that HSP70 is overexpressed in pancreatic cancer cells, and that the downregulation of HSPs leads to apoptosis. We have also demonstrated that one of the mechanisms by which HSP70 inhibits apoptosis in pancreatic cancer cells is by inhibiting Cyt c release from the mitochondria. However, the mechanism by which HSP70 inhibits Cyt c release from mitochondria remains unclear. We have observed that MUC1 is overexpressed in pancreatic cancer cells, where it also interacts with HSP70. We therefore hypothesize that HSP70 inhibits apoptosis in pancreatic cancer cells by transporting MUC1 to the mitochondria, where MUC1 stabilizes mitochondria, and subsequently prevents Cyt c release. Our preliminary studies indicate that downregulating HSP70 in pancreatic cancer cells leads to lysosomal membrane permeabilization and releases lysosomal enzymes into the cytosol, which then activate the apoptotic cascade. However, the mechanism by which HSP70 stabilizes the lysosomes remains unclear. Our preliminary studies suggest that MUC1 co-localizes to lysosomes. Thus, we hypothesize that HSP70 transports MUC1 to lysosomes, as well, and thereby stabilizes them. This novel hypothesis can explain the mechanism by which both HSP70 and MUC1 inhibit apoptosis in pancreatic cancer cells. The proposed studies have been divided into 4 specific aims: The 1st and 2nd specific aims will evaluate the role of MUC1 in the pathogenesis and aggressiveness of pancreatic cancer and will examine inhibiting MUC1 expression as a potential therapeutic strategy in pancreatic cancer;The 3rd and 4th aims will examine the mechanism by which MUC1 stabilizes lysosomes and mitochondria, and will investigate the role played by HSP70 in such processes. Once completed, these studies will greatly increase our understanding of the mechanisms by which cancer cells evade cell death, and will eventually lead us to design novel treatments.
Pancreatic cancer is the fourth leading cause of cancer-related death in the USA. The severity of this cancer can be appreciated by the fact that in 2006 alone, 33,730 new cases were expected, and almost the same number died of the disease. Thus, efforts to gain information on the pathobiology of pancreatic cancer and on the molecular mechanisms related to the invasion and metastasis of tumor cells are urgently needed in order to develop effective treatments.
