Previous studies from our laboratory have demonstrated that acidic extracellular pH and activation of c-Met by the Hepatocyte Growth Factor (HGF) in the tumor microenvironment, have the ability to induce anterograde (outward) lysosome trafficking in prostate tumor cells, resulting in an increase in protease secretion and tumor cell invasion. Lysosome redistribution requires microtubules, sodium proton exchangers (NHEs) and PI-3K activity. These processes can be blocked by preventing anterograde lysosome trafficking using NHE inhibitors or anti-diabetic drugs belonging to the thiazolidinedione class. Epidermal Growth Factor (EGF) is another growth factor that is commonly expressed in the tumor microenvironment, including prostate tumors, and is involved in activating a variety of processes leading to tumor progression. Upon binding of the EGF to Epidermal Growth Factor Receptor (EGFR), a variety of cellular survival and stress pathways are activated, ultimately resulting in cytoskeletal changes and altered gene expression that contribute to the increased motility and invasion of tumor cells. Interestingly, we have found that EGFR activation also induces anterograde lysosome trafficking and scattering in DU145 prostate cancer cells by a mechanism that is dissimilar to that of HGF-induced lysosome movement. For instance, we have determined that EGF anterograde lysosome trafficking and scattering is dependent on the activity of the mitogen activated protein kinase p38α, but is not dependent on the activity of PI3K. Conversely, HGF mediated lysosome trafficking and scattering is dependent on the activity of PI3K. Additionally, EGF induced peripheral lysosome movement appears to be independent of the activity of NHE 1 and 3, but treatment with the broad acting NHE inhibitor, EIPA [5-(N-ethyl-N-isopropyl)-amiloride], prevented EGF induced anterograde lysosome trafficking and promoted a clustering of lysosomes around the nucleus, suggesting that multiple NHEs are involved in EGF mediated lysosome trafficking. This was accompanied by a reduction in cell invasion through reconstituted basement membrane in a transwell invasion assay. Also, EGF-induced lysosome repositioning was reversed by troglitazone, an anti-diabetic agent. Together, these data further implicate lysosome positioning as critical to the process of HGF and EGF mediated tumor invasion and provide insight into the mechanism by which EGF induces peripheral lysosome trafficking. This information further supports the notion that inhibition of lysosome repositioning is a potentially viable therapeutic target to block HGF- and EGF-induced tumor cell invasion.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1071. doi:1538-7445.AM2012-1071