GLYCOSPHINGOLIPID ENRICHED MICRODOMAINS IN CANCER CELL INVASION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The ultimate goal for understanding and combating cancer progression is to investigate mechanisms culminating in an invasive and metastatic cell phenotype. Cancer cell invasion is a highly complex and multistep process, that is characterized by altered expression levels of cell adhesion molecules and secretion of proteolytic enzymes, along with changes in expression or activities of a variety of cellular proteins in multiple branching signaling pathways. In addition, the plasma membrane contains membrane microdomains enriched in tumor-associated glycosphingolipid (GSL)-antigens, that function as mediators of cell adhesion, and in signaling molecules, providing important locations for cell signaling. Recent studies showed that tumor cell invasion often results from aberrant signaling mechanisms initiated by differential organization and clustering of GSLs and/or membrane proteins, and their assembly with signaling molecules. The synthetic ether lipid analog ET-18-OMe (1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine) was previously shown to influence invasion of human breast and colon cancer cells and is used as a molecular probe to induce cellular invasion in order to explore changes in composition, translocation and organization of crucial molecules and the possible involvement of membrane microdomains. Our results show that reorganization, clustering and assembly of specific membrane proteins and signal transducers with glycosphingolipids in membrane microdomains are responsible for loss of cell-cell adhesion and subsequent result in increased invasiveness of MCF-7 breast cancer cells. Where loss of cell-cell adhesion was due to sterical hindrance of E-cadherin by episialin both localized in and associated with clusters of the glycosphingolipid, MSGb5, subsequent invasion resulted from activation of MSGb5-associated FAK/cSrc signaling complexes and downstream ERK, leading to increased expression and activation of MMPs. In contrast, the invasive behavior of HCT-8 colon cancer cells was initiated through clustering of integrin alpha1 subunits and the activation of associated FAK/cSrc complexes. The followed path downstream, however, appeared to be the p130Cas-JNK pathway also leading to increased expression of MMPs and did not involve specific association with glycosphingolipids. The latter results point out to the classic integrin-dependent invasion of cancer cells, initiated through clustering of integrins. In contrast, signaling towards invasion may also occur via GSLs, adhesion to the surrounding matrix mediated by the sugar moieties of glycosphingolipids resulting in GSL-dependent adhesion may then induce signaling events to alter cellular phenotype. Future work includes exploring alterations in glycosylation of membrane proteins and membrane microdomain glycosphingolipids involved in cancer cell invasion.