AHRR is sufficient to block milk production in HC11 mammary cells. HC11 cells were transduced with lentivirus to generate cell lines stably expressing HA-tagged AHRR (pEiZ-HA-AHRR) or a vector control (pEiZ). A, Western blot of lysates from stable cell lines probed for HA and α-tubulin (control). B, Stable HC11 cell lines were treated for 48 h with vehicle control (DMSO) or 10 µM 1023. Cyp1A1 mRNA levels were measured by qPCR and normalized to β-actin expression. Results are shown as normalized mean Cyp1A1 expression (± SEM). Asterisk indicates a statistically significant difference compared with treated vector control cells (****P ≤ .0001). C, Stable HC11 cell lines were induced with lactogenic hormones (LH) to produce milk proteins. β-Casein mRNA levels were measured by qPCR and normalized to β-actin expression. Results are shown as normalized mean β-casein expression (± SEM). Asterisk indicates a statistically significant difference compared with treated vector control cells (P ≤ .0001). D, Cell lysates were probed for β-casein and α-tubulin (control). E, An HC11 cell line was generated to express AHRR mutated to prevent SUMOylation in the C-terminal region (HA-AHRRmutant). All stable cell lines were induced with LH and probed for β-casein and α-tubulin (control) as before. Abbreviations: HA, hemagglutinin; AHRR, aryl hydrocarbon receptor repressor; LH, lactogenic hormones; DMSO, dimethyl sulfoxide; qPCR, real-time polymerase chain reaction.