Overexpression of caveolin‐1 in a human melanoma cell line results in dispersion of ganglioside GD3 from lipid rafts and alteration of leading edges, leading to attenuation of malignant properties

Abstract

Caveolin-1 is a component of lipid rafts, and is considered to be a tumor suppressor molecule. However, the mechanisms by which caveolin-1 functions in cancer cells are not well understood. We generated caveolin-1 transfectant cells (Cav-1 + cells) using a human melanoma cell line (SK-MEL-28) and investigated the effects of caveolin-1 overexpression on the GD3-mediated malignant properties of melanomas. Cav-1 + cells had decreased cell growth and motility, and reduced phosphorylation levels of p130Cas and paxillin relative to controls. In floatation analysis, although GD3 was mainly localized in glycolipid-enriched microdomain (GEM)/rafts in control cells, it was dispersed from GEM/rafts in Cav-1 + cells. Correspondingly, GD3 in Cav-1 + cells stained uniformly throughout the membrane, whereas control cells showed partial staining of the membrane, probably at the leading edge. p130Cas and paxillin were stained in the leading edges and colocalized with GD3 in the control cells. In contrast, these molecules were diffusely stained and no definite leading edges were detected in Cav-1 + cells. These results suggest that caveolin-1 regulates GD3-mediated malignant signals by altering GD3 distribution and leading edge formation. These results reveal one of the mechanisms by which caveolin-1 curtails the malignant properties of tumor cells. (Cancer Sci 2007; 98: 512-520)

Membrane sialidase NEU3 is highly expressed in human melanoma cells promoting cell growth with minimal changes in the composition of gangliosides

“…(34) Recent progress in the isolation and manipulation of glycosyltransferase cDNA enabled us to investigate the roles of these gangliosides in cancer phenotypes. (35) Since we cloned cDNA of GD3 synthase, (13) we have investigated roles of GD3 synthase in melanomas (25,27,31,36,37) and in small-cell lung carcinomas. (38,39) Consequently, it has been demonstrated that the melanoma-specific ganglioside GD3 plays crucial roles in increased proliferation, enhanced invasion and cell adhesion in melanoma cells.…”

“…(26) The TLC was developed with a solvent system of chloroform:methanol:0.2% CaCl 2 ⁄ water (55:45:10), and bands were detected with resorcinol spray as described previously. (27) Sialidase assay. Sialidase activity was assayed with gangliosides mixture or GM3 as substrates and Triton X-100 as described previously.…”

Caveolin-1 in Melanoma Progression

“…In cells expressing caveolin-1, GD3 becomes homogeneously distributed in the membrane, rather than concentrated in specific regions. Hence, caveolin-1 is suggested to function as a tumor suppressor in melanoma cells by disrupting GD3-mediated malignant signaling (Nakashima, Hamamura et al 2007). Alternatively, for a non-cutaneous, retinal melanoma, increased caveolin-1 expression was associated with enhanced malignancy.…”

Positive Feedback Loop Between PI3K-Akt-mTORC1 Signaling and the Lipogenic Pathway Boosts Akt Signaling: Induction of the Lipogenic Pathway by a Melanoma Antigen

“…Cell proliferation was determined by MTT assay (23). On day 0, cells were seeded in 96-well plates (3,000 cells/well) in medium A.…”

“…We and others showed that GD3 enhances proliferation and invasive activity of melanoma and other cells (19)(20)(21)(22) although the molecular mechanism remains poorly understood. GD3 mediates such functions in membrane microdomains known as lipid rafts where cholesterol and sphingolipids are enriched (23). Lipid rafts are essential for various cellular functions (24).…”