g(m3)-ganglioside and Carcinoma

GRP94 is an ATP-dependent chaperone able to regulate pro-oncogenic signaling pathways. Previous studies have shown a critical role of GRP94 in brain metastasis (BrM) pathogenesis and progression. In this work, an untargeted lipidomic analysis revealed that some lipid species were altered in GRP94-deficient cells, specially GM2 and GM3 gangliosides. The catalytic pathway of GM2 is affected by the low enzymatic activity of β-Hexosaminidase (HexA), responsible for the hydrolysis of GM2 to GM3. Moreover, a deficiency of the GM2-activator protein (GM2-AP), the cofactor of HexA, is observed without alteration of gene expression, indicating a post-transcriptional alteration of GM2-AP in the GRP94-ablated cells. One plausible explanation of these observations is that GM2-AP is a client of GRP94, resulting in defective GM2 catabolic processing and lysosomal accumulation of GM2 in GRP94-ablated cells. Overall, given the role of gangliosides in cell surface dynamics and signaling, their imbalance might be linked to modifications of cell behaviour acquired in BrM progression. This work indicates that GM2-AP could be an important factor in ganglioside balance maintenance. These findings highlight the relevance of GM3 and GM2 gangliosides in BrM and reveal GM2-AP as a promising diagnosis and therapeutic target in BrM research.

Topics: Animals; beta-Hexosaminidase alpha Chain; Brain Neoplasms; Carcinoma; Cell Line, Tumor; Culture Media, Conditioned; Down-Regulation; Female; G(M2) Activator Protein; G(M2) Ganglioside; G(M3) Ganglioside; Gene Expression Regulation, Neoplastic; Genes, Reporter; Humans; Lipidomics; Lysosomes; Membrane Glycoproteins; Mice; Neoplasm Proteins; RNA Interference; RNA, Small Interfering; Triple Negative Breast Neoplasms

Gangliosides have been described as modulators of growth factor receptor activity and subsequent cellular function. Due to the lower-pH environment found in tumor cells, ganglosides are thought to be formed (at least to some extent) into their lactone forms. The aim of the study was to analyze the mode of action of the lactone of the ganglioside GM3 on epidermal growth factor (EGF) signaling in human ovarial epidermoid carcinoma A431 cells and cell growth in human oral epidermoid carcinoma KB cells by applying the GM3 lactone analog HK1-ceramide 2, which is stable under hydrolytic conditions. Specific inhibition of EGF-dependent receptor tyrosine phosphorylation was observed by HK1-ceramide 2 at 25 microM, whereas GM3 showed a comparable inhibition at eightfold higher concentrations. In cells exposed to low pH, where GM3 is thought to form its lactone to a higher extent, addition of GM3 showed no further inhibitory effect on EGF-dependent receptor phosphorylation. Similarly to GM3, HK1-ceramide 2 does not affect binding of (125)I-EGF to the cell surface receptor. EGF-dependent growth of KB cells was also found to be inhibited by HK1-ceramide 2 at much lower concentrations compared to GM3. In conclusion, our results indicate that the GM3 lactone analog HK1-ceramide 2 is a specific inhibitor of EGF receptor function and is more potent in reducing EGF-dependent tyrosine phosphorylation of the receptor in A431 cells and in inhibiting EGF-dependent growth of KB cells compared to GM3.

Topics: Carcinoma; Cell Division; Ceramides; Dose-Response Relationship, Drug; ErbB Receptors; Female; G(M3) Ganglioside; Glycosphingolipids; Humans; Hydrogen-Ion Concentration; KB Cells; Lactones; Ovarian Neoplasms; Phosphorylation; Receptors, Cell Surface; Tumor Cells, Cultured

The patterns of gangliosides and phospholipids and their relation to TSH response were examined in twenty-six malignant thyroid tumors (4 follicular, 6 papillary, 5 medullary, 11 anaplastic carcinomas) and thirty-six hyperplastic goiters. Thirteen thyroid tissues adjacent to benign tumors with no evidence of macroscopic or microscopic abnormalities were used as normal tissue. In normal thyroids the major ganglioside was GD3 (44%) and GM3 was the second ganglioside (20%). In minor amounts GD1a (8.6%), GD1b (6.2%), GT1b (5.7%) and GM1 (5.6%) were present. In hyperplastic goiters and in follicular carcinomas the patterns of gangliosides were similar to that of normal tissue except for GM3 which, in the last tissue, was higher (34%). In papillary carcinomas low levels of GM3 (11%) and GT1b (0.8%) with a high level of GD1b (12.6%) were found. In anaplastic carcinomas GM3 was very high (47%) whereas GD3 was low (18%). In these tumors also a high percentage (14.0%) of GD1a was found. In medullary carcinomas the lowest levels of GM3 (4%) with the highest level of GD3 (64%) were found. Although large differences of the gangliosides distribution were clearly encountered in the various pathological human thyroid, no correlation between lack of TSH response and some individual ganglioside could be made. No differences in the individual phospholipid in the various tissues studied were found.

Topics: Adenocarcinoma; Carcinoma; Carcinoma, Papillary; G(M3) Ganglioside; Gangliosides; Humans; Phospholipids; Thyroid Gland; Thyroid Neoplasms; Thyrotropin