Processing and expression of c-Kit and EPOR in HCD57 and HCD57-SREI cells. (A) HCD57 cells deprived of EPO overnight (lanes A through D) or HCD57-SREI cells cultured without EPO (lanes D through G) were left untreated (lanes A and E), or treated with 10 U EPO/mL for the indicated times at 37°C. The cells were rapidly cooled, and the forms of EPOR present were determined by immunoprecipitation of the EPOR and detection of the receptor proteins using the same affinity-purified anti-COOH terminal, anti-EPOR IgG. The form of EPOR between 62 and 78 kD are marked (upper arrows). The IgG on the gel from the heavy chain of anti-EPOR present in the immunoprecipitates is also indicated (lower arrow). (B) HCD57-SREI cells exhibit upregulated cell-surface c-Kit expression. HCD57 and HCD57-SREI cells were incubated with an FITC-conjugated c-Kit antibody and detected using flow cytometry. HCD57-SREI cells exhibit 81.4% more cell surface c-Kit (peak C) than HCD57 (peak B). Peak A represents background staining (CD4).