To investigate the molecular mechanisms of gangliosides for the regulation of cell proliferation, Swiss 3T3 cells were transfected with GM2/GD2 synthase and GM1 synthase cDNAs, resulting in the establishment of GM1-expressing (GM1(+)) lines. Compared with the vector control (GM1(-)) cell lines, GM1(+) cells exhibited reduced cell proliferation by stimulation with platelet-derived growth factor (PDGF). In accordance with the reduced cell growth, GM1(+) cells showed earlier decreases in the phosphorylation levels of PDGF receptor and less activation of MAP kinases than GM1(-) cells. To analyze the effects of GM1 expression on the PDGF/PDGF receptor (PDGFR) signals, the glycolipid-enriched microdomain (GEM) was isolated and the following results were obtained. (i) PDGFR predominantly distributed in the non-GEM fraction in GM1(+) cells, while it was present in both GEM and non-GEM fractions in GM1(-) cells. (ii) Activation of PDGFR as detected by anti-phosphotyrosine antibody occurred almost in parallel with existing amounts of PDGFR in each fraction. (iii) GM1 binds with PDGFR in GEM fractions. These findings suggested that GM1 regulates signals via PDGF/PDGFR by controlling the distribution of PDGFR in- and outside of GEM, and also interacting with PDGFR in the GEM fraction as a functional constituent of the microdomain.