CHEK2 and acquired polycythemia vera: In contrast to strong Chk2 activation in CML cells, lysates prepared from cells obtained from PV patients in their proliferative phase showed only modest evidence of activated Chk2 (i.e., displayed lower signal of phosphorylated Chk2 compared to CML cells), whereas the unphosphorylated form of Chk2 was barely detectable in these samples (Figure 1b).