CSF2 and leukemia: To gain insight into the molecular machinery required for the ubiquitination and degradation of CSF2RB, we employed a CRISPR/Cas9 screen using the CSF2RB reporter and a previously described ubiquitin ligase–specific single-guide RNA (sgRNA) library (14) in two human leukemia cell lines that endogenously respond to GM-CSF, TF1, and THP1 cells.