Background & Purpose: The constitutive androstane receptor (CAR) belongs to nuclear receptor superfamily. The administration of CAR agonist TCPOBOP to mice leads to hepatomegaly but the mechanism is unclear. Yes-associated protein (YAP) is a downstream factor of Hippo signaling pathway, which is a potent regulator of organ size and tissue homeostasis. This study examined the role of YAP in CAR-promoted hepatomegaly and liver regeneration. Experimental Approach: The effect of CAR on liver enlargement and liver regeneration was evaluated in wild-type (WT) mice, liver-specific YAP-deficient mice, and partial hepatectomy (PHx) mice. KI67 and CTNNB1 staining were performed to evaluate the proliferation response and hepatocytes size. The protein levels of YAP and its downstream targets were measured and Co-IP was conducted to explore the protein-protein interaction between CAR and YAP. Key Results: The results suggested TCPOBOP increases the liver/body weight ratio in WT mice and PHx mice. Hepatocytes enlargement occurred around the central vein area, while the number of KI67+ cells increased around portal vein area. The translocation of YAP was induced and its downstream targets were upregulated after CAR activation via TCPOBOP. Co-IP results revealed a potential protein-protein interaction between CAR and YAP. However, CAR-induced hepatomegaly was still observed in Yap-/- mice. Conclusion and Implications: CAR activation promotes hepatomegaly and liver regeneration in part by inducing nuclear translocation of YAP and interaction with YAP pathway, which provides new insights for understanding the physiological functions of CAR, and suggests the potential for manipulation of liver size.

Background & Purpose: The constitutive androstane receptor (CAR) belongs to nuclear receptor superfamily. The administration of CAR agonist TCPOBOP to mice leads to hepatomegaly but the mechanism is unclear. Yes-associated protein (YAP) is a downstream factor of Hippo signaling pathway, which is a potent regulator of organ size and tissue homeostasis. This study examined the role of YAP in CAR-promoted hepatomegaly and liver regeneration. Experimental Approach: The effect of CAR on liver enlargement and liver regeneration was evaluated in wild-type (WT) mice, liver-specific YAP-deficient mice, and partial hepatectomy (PHx) mice. KI67 and CTNNB1 staining were performed to evaluate the proliferation response and hepatocytes size. The protein levels of YAP and its downstream targets were measured and Co-IP was conducted to explore the protein-protein interaction between CAR and YAP. Key Results: The results suggested TCPOBOP increases the liver/body weight ratio in WT mice and PHx mice. Hepatocytes enlargement occurred around the central vein area, while the number of KI67+ cells increased around portal vein area. The translocation of YAP was induced and its downstream targets were upregulated after CAR activation via TCPOBOP. Co-IP results revealed a potential protein-protein interaction between CAR and YAP. However, CAR-induced hepatomegaly was still observed in Yap-/- mice. Conclusion and Implications: CAR activation promotes hepatomegaly and liver regeneration in part by inducing nuclear translocation of YAP and interaction with YAP pathway, which provides new insights for understanding the physiological functions of CAR, and suggests the potential for manipulation of liver size.