Variants of BALB/c 3T3 cells lacking complex gangliosides retain a fibronectin matrix and spread normally on fibronectin-coated substrates

Evidence has accumulated that di- and trisialogangliosides are involved in the interaction of cells with fibronectin. We have therefore tested the ability of variants of BALB/c 3T3 deficient in such gangliosides to organize a fibronectin matrix and to spread on fibronectin-coated substrates. Whereas BALB/c 3T3 cells contained gangliosides GM3, GM1, and GD1a, direct chemical analysis showed that five out of six variants isolated contained no detectable GD1a. By the overlaying of thin layer chromatograms of cellular gangliosides with 125I-cholera toxin, these variants were also found to lack ganglioside GM1. In contrast, the sialogalactoprotein profile of these cells, analyzed using an 125I-ricin/SDS polyacrylamide gel overlay technique, was similar to that of the parent cell line. All variants organized an extensive fibronectin matrix comparable to that of BALB/c 3T3, as shown using either immunofluorescence or lactoperoxidase-catalyzed iodination. The variants could also spread on fibronectin-coated substrates and adopt a morphology similar to that of BALB/c 3T3 cells, with little or no difference in the concentration of fibronectin required for 50% cell spreading. Cell spreading of the variants was accompanied by the formation of focal contacts and microfilament bundles, in a manner closely resembling that seen with BALB/c 3T3 cells. Treatment of BALB/c 3T3 cells with neuraminidase, which converts much of the cellular GD1a to GM1, did not affect cell spreading on fibronectin. The results clearly demonstrate that complex gangliosides are not essential for retention of a fibronectin matrix or for spreading on fibronectin-coated substrates.