title: Ganglioside GM3 promotes carcinoma cell proliferation via urokinase plasminogen activator-induced extracellular signal-regulated kinase-independent p70S6 kinase signaling.
abstract: Overexpression of NeuAcalpha2-3Galbeta1-4Glcbeta1-Cer (GM3), a major ganglioside of cutaneous tumor cell membranes, inhibits ligand-dependent and ligand-independent activation of the epidermal growth factor (EGF) receptor in normal and neoplastic epithelial cells. This leads to the suppression of Ras/extracellular signal-regulated kinase (ERK) activation and, in the presence of EGF or fibronectin, inhibits cell proliferation. However, some tumor cells show increased levels of GM3, and vaccines that target GM3 can inhibit the growth of neoplastic cells in vivo, especially melanomas. We report that in the presence of urokinase plasminogen activator (uPA), overexpression of GM3 paradoxically increases the proliferation of carcinoma cells by augmenting ERK-independent p70S6 kinase activation. Functional blockade of uPA receptor (uPAR) or inhibition of p70S6 kinase, but not inhibition of Ras/ERK signaling, suppresses this GM3-induced stimulation of cell proliferation. The ERK-independent activation of p70S6 kinase involves phosphorylation at threonine-389, threonine-421/serine-424, and serine-411 sites with intermediate phosphatidylinositol 3 kinase and protein kinase C-zeta activation. These studies implicate gangliosides as enhancers of uPAR-related signaling and suggest that the response to GM3 depends on the local concentration of uPA. Therapeutic modalities that target or supplement gangliosides may require concomitant treatment that suppresses EGFR or uPAR signaling, respectively, to control neoplastic cell proliferation.
authors.affiliation: Department of Dermatology, Northwestern University's Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Xiao-Qi
authors.initials: XQ
authors.lastname: Wang
authors.forename: Ping
authors.initials: P
authors.lastname: Sun
authors.forename: Linda
authors.initials: L
authors.lastname: Go
authors.forename: Viola
authors.initials: V
authors.lastname: Koti
authors.forename: Margarita
authors.initials: M
authors.lastname: Fliman
authors.forename: Amy S
authors.initials: AS
authors.lastname: Paller
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005679:G(M3) Ganglioside / Q000378:metabolism*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction; D014568:Urokinase-Type Plasminogen Activator / Q000494:pharmacology*
chemical_list: D005679:G(M3) Ganglioside; D018809:Proliferating Cell Nuclear Antigen; D019869:Phosphatidylinositol 3-Kinases; C087857:protein kinase C gamma; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D014568:Urokinase-Type Plasminogen Activator