ARNT is required for milk production in HC11 mammary cells. A, Lentiviral shRNA constructs (shARNT#1 and shARNT#2) were used to stably knockdown ARNT expression in HC11 cells. ARNT expression was measured by qPCR, normalized to β-actin expression, and compared with HC11 cells stably expressing a control shRNA (Control). Results are shown as normalized mean ARNT expression (±SEM). Asterisk indicates a statistically significant difference compared with control shRNA cells (*P ≤ 0.05). B, ARNT protein levels were measured in cell lysates from stable lines. Western blot of lysates probed for ARNT and α-tubulin (control). 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 control cells (P ≤ 0.0001). D, Western blot of lysates probed for β-casein and α-tubulin (control). Abbreviations: ARNT, aryl hydrocarbon receptor nuclear translocator; LH, lactogenic hormones; qPCR, real-time polymerase chain reaction.