EpoR mRNA and protein levels for representative tumor cell lines. (A) EPOR mRNA levels were determined by bDNA assay from cell lysates (n = 3 from each culture). Expression of EPOR was normalized to the level of 18S rRNA and is expressed as a percentage of control (POC; 100% = EPOR mRNA levels in UT-7/Epo cells). (B) EpoR protein in lysates from the indicated cell lines: 2-fold serial dilutions of purified EpoR extracellular domain protein (EpoR ECD amino acid 1-225) and cell lysates were subjected to SDS-PAGE and Western blotting with detection of EpoR by mAb A82. Direct comparison of band intensities of the 59-kDa EpoR protein with those of the purified EpoR ECD was used to estimate EpoR dimers/cell. NSCLC indicates non–small cell lung carcinoma; SCLC, small cell lung carcinoma; and Ery. Pro., erythroid progenitor cells.