Proteasome subunit up-regulation in β-thalassemia is Nrf1 dependent. (A-B) Wild-type murine fetal liver erythroid cultures were treated for 24 hours with 1μM sulforaphane or 0.1μM MG132 to activate Nrf2 or Nrf1, respectively. (A) Expression of Nqo1, an Nrf2 target gene; n = 4 embryos/group. ***P < .001 versus control (CTRL). (B) Proteasome subunit mRNA expression (average fold change of 3 randomly selected subunits) normalized to control. (C-G) Wild-type fetal liver erythroid precursors were infected with retroviruses encoding control (anti-luciferase, Luc), Nrf1, or Nrf2 targeted shRNAs and differentiated for 24 hours with or without 0.1μM MG132. As an additional control, Luc shRNA–infected cells were also heat-shocked at 42°C for 1 hour and allowed to recover for 1 hour at 37°C (HS). Transcript expression was normalized to β-actin and Hprt mRNAs and compared among experimental groups with control-treated Luc shRNA samples assigned an arbitrary value of 1.0. Proteasome subunit expression is shown as the average fold change of an expanded panel of 9 proteasome subunit mRNAs (C), Nrf1 (D), Nrf2 (E), Nqo1 (F), and Hsp105 (G); n = 3 embryos per group. **P < .01 versus Luc Ctrl; ***P < .001 versus Luc Ctrl; ##P < .01 versus Luc MG132; ###P < .001 versus +/+ Luc. (H) Proteasome subunit mRNA expression in wild-type or Th3/Th3 fetal liver erythroblasts infected with retroviruses expressing shRNAs targeting Nrf1, Nrf2, or luciferase (Luc). Analysis was performed after 48 hours of expansion and 44 hours of differentiation. Data shown are the average fold change for 9 subunit transcripts; n = 3 embryos/group. *P < .05 versus +/+ Luc; **P < .01 versus +/+ Luc, #P < .05 versus Th3/Th3 Luc; ## P < .001 versus +/+ Luc.