EPO regulation of cyclin G2, cyclin D2, p27, and Bcl6 via minimal EPOR-H and EPOR-HM alleles. (A) EPO up-modulation of cyclin D2 and down-modulation of cyclin G2 depend on EPOR PY343 signals. Kit^posCD71^high cells were prepared from wt-EPOR, EPOR-HM, and EPOR-H erythroblasts. Hematopoietic cytokines were withdrawn for 5.5 hours. Cells then were exposed to EPO (5 U/mL). At 90 minutes, RNA was isolated, and reverse transcribed. Cyclin D2, Cyclin G2, Cdkn1b, and Bcl6 transcript levels then were determined by quantitative PCR. Values are the means (± SD) of n = 3 independent samples. (B) Observed EPO modulation of cell-cycle regulatory genes via wt-EPOR, EPOR-HM, and EPOR-H alleles provided for a mapping of transcriptional circuits to key EPOR subdomains including an EPOR box1-plus-JAK2 pathway to Myc, Nupr1, Egr1, and Nab2; an EPOR/PY343/STAT5 pathway to Cyclin D2 and Nupr1 expression, and Cyclin G2, Cdkn1b, and Bcl6 and Nab2 repression; and EPOR distal domain effects on Gspt1 induction.