RNA was extracted from EML cells that were treated with SCF plus the indicated HGF in the presence or absence of atRA according to the procedures described in Materials and Methods. Northern blots of EML RNA were probed with D3 resulting in no expression (−), low expression (+), or moderate/high expression (+++). Northern blots were reprobed with G3PDH to verify equal loading in all samples. The presence (+) or absence (−) of biologically active receptors was determined in proliferation assays with EML cells using single cytokines as described in Materials and Methods.