Figure 3.

TRIM21 affects the total levels of PDGFRβ at the cell surface. (a,b) Total levels of PDGFRβ are increased on the cell surface after depletion of TRIM21. TRIM21 was transiently knocked-down in U2OS cells and cells were serum-starved overnight. After stimulation for the indicated periods of time with PDGF-BB, cell surface proteins were biotinylated and cells were lysed and incubated with streptavidin (ST)-agarose (Str. PD; streptavidin pulldown) and immunoblotted (Ib) for PDGFRβ and transferrin receptor (TfR). Total cell lysates (TCL) were immunoblotted for PDGFRβ, TRIM21 and α-tubulin. Quantification of three experiments is presented in (b). (c,d) Induction of TRIM21 in tet-inducible U2OS-TRIM21 cell line downregulates total levels of PDGFRβ on the cell surface (c). The experiment was performed using the protocol described in (a). Quantification of four experiments is presented in (d).