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Aryl hydrocarbon receptor (AhR) is primarily involved in the transcriptional regulation of CYP1A enzymes, which are the main catalysts of the metabolic activation or inactivation of numerous procarcinogens, carcinogens, environmental toxicants, or therapeutic agents. Several endogenous factors, including hormones, can modify CYP1A induction, directly influencing CYP1A gene expression or AhR function or indirectly via crosstalks with other transcription factors. In this article, we summarize the current knowledge about the role of hormones (i.e., glucocorticoids, estrogens, progesterone, androgens, insulin, and glucagon) and hormone receptors as well as other essential factors (e.g., vitamin D, retinoids) in the modulation of CYP1A expression.

The body defends itself against potentially harmful compounds, such as drugs and toxic endogenous compounds and their metabolites, by inducing the expression of enzymes and transporters involved in their metabolism and elimination. The orphan nuclear receptor CAR (NR1I3 controls phase I (CYP2B, CYP2C, CYP3A), phase II (UGT1A1), and transporter (SLC21A6, MRP2) genes involved in drug metabolism and bilirubin clearance. Constitutive androstane receptor (CAR) is activated by xenobiotics, such as phenobarbital, but also by toxic endogenous compounds such as bilirubin metabolite(s). To better understand the inter- and intravariability in drug detoxification, we studied the molecular mechanisms involved in CAR gene expression in human hepatocytes. We clearly identified CAR as a glucocorticoid receptor (GR) target gene, and we proposed the hypothesis of a signal transduction where the activation of GR plays a critical function in CAR-mediated cellular response. According to our model, chemicals or pathophysiological factors that affect GR function should decrease CAR function. To test this hypothesis, we recently investigated the effect of microtubule disrupting agents (MIAs) or proinflammatory cytokines. These compounds are well-known inhibitors of GR transactivation property. MIAs activate c-Jun N-terminal kinase (JNK), which phosphorylates and inactivates GR, whereas proinflammatory cytokines, such as IL-6 or IL1beta, induce AP-1 or NF-kB activation, respectively, leading to GR inhibition. As expected, we observed that these molecules inhibit both CAR gene expression and phenobarbital-mediated CYP gene expression in human hepatocytes.