Differential impact of lipid raft depletion on platelet-derived growth factor (PDGF)-induced ERK1/2 MAP-kinase, SRC and AKT signaling.

It has become clear that lipid rafts functions as signaling hotspots connecting cell surface receptors to intracellular signaling pathways. However, the exact involvement of lipid rafts in receptor tyrosine kinase signaling is still poorly understood. In this study, we have analyzed platelet-derived growth factor (PDGF) receptor ß (PDGFR-ß) signaling in two different cell lines depleted of cholesterol, and as a consequence, disruption of lipid rafts. Cholesterol depletion of BJ-hTERT fibroblasts using methyl-ß-cyclodextrin (MßCD) did not affect PDGFR-ß activation as measured by its tyrosine phosphorylation. However, we did observe a small reduction in AKT phosphorylation and a more robust decrease of ERK1/2 activation. In contrast, in the osteosarcoma cell line U2OS, we noticed a deficient receptor activation. Interestingly, in U2OS cells, the ERK1/2 pathway was unaffected, but instead AKT and SRC signaling was reduced. These results suggest that cell type specific wiring of signaling pathways can lead to differential sensitivity to cholesterol depletion. Furthermore, MßCD treatment had a much more pronounced morphological effect on U2OS compared to BJ-hTERT cells. This is consistent with a previous report claiming that cancer cells are more sensitive to cholesterol depletion than normal cells. Our data supports the possibility that cholesterol lowering drugs may impede tumor growth.