Increased tumorigenicity and invasiveness of C6 rat glioma cells transfected with the human alpha-2,8 sialyltransferase cDNA

Gangliosides are thought to be involved in tumor cell proliferation, migration and invasiveness as so far demonstrated by the addition of exogenous gangliosides to the culture medium. To better understand the direct influence that alterations in ganglioside synthesis can exert on these functional aspects of cell biology, in the present study, we investigated the behaviour of C6 rat glioma cells after stable transfection with the human CMP-NeuAc:NeuAcalpha2-3Galbeta1-4GlcCer alpha2,8-sialyltransferase (SAT-II, EC 2.4.99.8) gene. The enzyme synthesizes ganglioside GD(3) by adding a sialic acid residue to ganglioside GM(3). Stable transfection of the constructs into C6 cells and expression of the human SAT-II gene were evaluated using PCR and RT-PCR amplification, respectively. Qualitative and quantitative analysis of the ganglioside profile was performed by conventional HP-TLC and identity of de novo synthesized species was assessed by TLC immunostaining. Results show that whereas C6 parental cells and C6 cells transfected with the empty expression vector synthesize, almost exclusively, ganglioside GM(3), de novo synthesis of GD(3) is clearly observed in clones expressing the alpha2,8-sialyltransferase. Subcutaneous grafting in athymic nude mice of cells expressing high levels of GD(3) induces tumors growing faster and more aggressively than controls. In in vitro assays, the same cells demonstrate increased proliferation rate, motility and invasiveness. Chemotaxis and chemoinvasion were assayed using the modified Boyden chamber. Data obtained suggest that endogenously neosynthesized GD(3) is able to modify proliferation rate, motility and invasion of C6 rat glioma cells, enhancing the features of malignancy of this tumor cell line.