Letter | Published:

Radixin deficiency causes conjugated hyperbilirubinemia with loss of Mrp2 from bile canalicular membranes

Nature Genetics volume 31, pages 320325 (2002) | Download Citation



The ezrin-radixin-moesin (ERM) family of proteins crosslink actin filaments and integral membrane proteins1,2,3. Radixin (encoded by Rdx) is the dominant ERM protein in the liver of wildtype mice4,5 and is concentrated at bile canalicular membranes (BCMs)5. Here we show that Rdx−/− mice are normal at birth, but their serum concentrations of conjugated bilirubin begin to increase gradually around 4 weeks, and they show mild liver injury after 8 weeks. This phenotype is similar to human conjugated hyperbilirubinemia in Dubin-Johnson syndrome6,7, which is caused by mutations in the multidrug resistance protein 2 (MRP2, gene symbol ABCC2)8,9,10,11, although this syndrome is not associated with overt liver injury. In wildtype mice, Mrp2 concentrates at BCMs to secrete conjugated bilirubin into bile8,11,12. In the BCMs of Rdx−/− mice, Mrp2 is decreased compared with other BCM proteins such as dipeptidyl peptidase IV (CD26) and P-glycoproteins. In vitro binding studies show that radixin associates directly with the carboxy-terminal cytoplasmic domain of human MRP2. These findings indicate that radixin is required for secretion of conjugated bilirubin through its support of Mrp2 localization at BCMs.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.




  1. 1.

    , & ERM proteins in cell adhesion and membrane dynamics. Trends Cell Biol. 9, 187–192 (1999).

  2. 2.

    & Cortical actin organization: lessons from ERM (Ezrin/Radixin/ Moesin) proteins. J. Biol. Chem. 274, 34507–34510 (1999).

  3. 3.

    , , & ERM-merlin and EBP50 protein families in plasma membrane organization and function. Annu. Rev. Cell Dev. Biol. 16, 113–143 (2000).

  4. 4.

    et al. A gene family consisting of ezrin, radixin, and moesin. Its specific localization at actin filament/plasma membrane association sites. J. Cell Sci. 103, 131–143 (1992).

  5. 5.

    et al. Ezrin-radixin-moesin-binding phosphoprotein 50 is expressed at the apical membrane of rat liver epithelia. Hepatology 33, 166–176 (2001).

  6. 6.

    & Chronic idiopathic jaundice with unidentified pigment in liver cells: a new clinicopathologic entity with report of 12 cases. Medicine 33, 155–179 (1954).

  7. 7.

    & Persistent nonhemolytic hyperbilirubinemia associated with lipochrome-like pigment in liver cells; report of four cases. Ann. Intern. Med. 41, 952–962 (1954).

  8. 8.

    , , & Absence of the canalicular isoform of the MRP gene-encoded conjugate export pump from the hepatocytes in Dubin-Johnson syndrome. Hepatology 23, 1061–1066 (1996).

  9. 9.

    et al. cDNA cloning of the hepatocyte canalicular isoform of the multidrug resistance protein, cMrp, reveals a novel conjugate export pump deficient in hyperbilirubinemic mutant rats. J. Biol. Chem. 271, 15091–15098 (1996).

  10. 10.

    et al. A mutation in the human canalicular multispecific organic anion transporter gene causes the Dubin-Johnson syndrome. Hepatology 25, 1539–1542 (1997).

  11. 11.

    et al. Impaired protein maturation of the conjugate export pump multidrug resistance protein 2 as a consequence of a deletion mutation in Dubin-Johnson syndrome. Hepatology 32, 1317–1328 (2000).

  12. 12.

    et al. Conjugate export pumps of the multidrug resistance protein (MRP) family: localization, substrate specificity, and Mrp2-mediated drug resistance. Biochim. Biophys. Acta 1461, 377–394 (1999).

  13. 13.

    et al. ERM family members as molecular linkers between the cell surface glycoprotein CD44 and actin-based cytoskeletons. J. Cell Biol. 126, 391–401 (1994).

  14. 14.

    et al. Ezrin/radixin/moesin (ERM) proteins bind to a positively charged amino acid cluster in the juxta-membrane cytoplasmic domain of CD44, CD43, and ICAM-2. J. Cell Biol. 140, 885–895 (1998).

  15. 15.

    , & Identification of EBP50: a PDZ-containing phosphoprotein that associates with members of the ezrin-radixin-moesin family. J. Cell Biol. 139, 169–179 (1997).

  16. 16.

    et al. Regulation mechanism of ERM (ezrin/radixin/moesin) protein/plasma membrane association: possible involvement of phosphatidylinositol turnover and Rho-dependent signaling pathway. J. Cell Biol. 135, 37–51 (1996).

  17. 17.

    et al. Direct interaction of the Rho GDP dissociation inhibitor with ezrin/radixin/moesin initiates the activation of the Rho small G protein. J. Biol. Chem. 272, 23371–23375 (1997).

  18. 18.

    et al. The TSC1 tumour suppressor hamartin regulates cell adhesion through ERM proteins and the GTPase Rho. Nature Cell Biol. 2, 281–287 (2000).

  19. 19.

    et al. Congenital jaundice in rats with a mutation in a multidrug resistance-associated protein gene. Science 271, 1126–1128 (1996).

  20. 20.

    et al. The 220-kD protein colocalizing with cadherins in non-epithelial cells is identical to ZO-1, a tight junction-associated protein in epithelial cells: cDNA cloning and immunoelectron microscopy. J. Cell Biol. 121, 491–502 (1993).

  21. 21.

    , , & Identification of a sister gene to P-glycoprotein. Cancer Res. 55, 2029–2034 (1995).

  22. 22.

    , , , & Direct binding of Na+-H+ exchanger NHE1 to ERM proteins regulates the cortical cytoskeleton and cell shape independently of H+ translocation. Mol. Cell 6, 1425–1436 (2000).

  23. 23.

    et al. Structural requirements for the apical sorting of human multidrug resistance protein 2 (ABCC2). Eur. J. Biochem. 269, 1866–1876, (2002).

  24. 24.

    et al. PDZK1, a novel PDZ domain-containing protein up-regulated in carcinomas and mapped to chromosome 1q21, interacts with cMOAT (MRP2), the multidrug resistance-associated protein. Lab. Invest. 79, 1161–1170 (1999).

  25. 25.

    et al. Normal development of mice and unimpaired cell adhesion/cell motility/actin-based cytoskeleton without compensatory up-regulation of ezrin or radixin in moesin gene knockout. J. Biol. Chem. 274, 2315–2321 (1999).

  26. 26.

    et al. ERM (ezrin/radixin/moesin)-based molecular mechanism of microvillar breakdown at an early stage of apoptosis. J. Cell Biol. 139, 749–758 (1997).

  27. 27.

    et al. Drug resistance and ATP-dependent conjugate transport mediated by the apical multidrug resistance protein, MRP2, permanently expressed in human and canine cells. Mol. Pharmacol. 55, 929–937 (1999).

  28. 28.

    , , , & Expression of the apical conjugate export pump, Mrp2, in the polarized hepatoma cell line, WIF-B. Hepatology 28, 1332–1340 (1998).

  29. 29.

    , & Quantitative expression of Oct-3/4 defines differentiation, dedifferentiation or self-renewal of ES cells. Nature Genet. 24, 372–376 (2000).

  30. 30.

    et al. Rho-kinase phosphorylates COOH-terminal threonines of ezrin/radixin/moesin (ERM) proteins and regulates their head-to-tail association. J. Cell Biol. 140, 647–657 (1998).

Download references


We thank T. Noda for discussions and J. Yamane for preparing bile canalicular fractions. This work was supported in part by a Grant-in-Aid for Scientific Research (B) (to Sa.T.) and a Grant-in-Aid for Cancer Research (to Sh.T.) from the Ministry of Education, Science and Culture of Japan, and grants from the Deutsche Forschunggemeinshaft (to D.K.).

Author information

Author notes

    • Shojiro Kikuchi
    •  & Masaki Hata

    These authors contributed equally to this work.


  1. Department of Cell Biology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.

    • Shojiro Kikuchi
    • , Kanehisa Fukumoto
    • , Yukari Yamane
    • , Takeshi Matsui
    • , Atsushi Tamura
    • , Shoichiro Tsukita
    •  & Sachiko Tsukita
  2. Department of Surgery, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kyoto 602-8566, Japan.

    • Shojiro Kikuchi
    • , Kanehisa Fukumoto
    •  & Hisakazu Yamagishi
  3. KAN Research Institute, Kyoto Research Park, Shimogyo-ku, Kyoto 600-8815, Japan.

    • Masaki Hata
    •  & Takeshi Matsui
  4. Laboratory for Cellular Morphogenesis, RIKEN Center for Developmental Biology, Chuo-ku, Kobe 650-0047, Japan.

    • Shigenobu Yonemura
  5. Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, D-69120 Heidelberg, Germany.

    • Dietrich Keppler
  6. College of Medical Technology, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.

    • Sachiko Tsukita


  1. Search for Shojiro Kikuchi in:

  2. Search for Masaki Hata in:

  3. Search for Kanehisa Fukumoto in:

  4. Search for Yukari Yamane in:

  5. Search for Takeshi Matsui in:

  6. Search for Atsushi Tamura in:

  7. Search for Shigenobu Yonemura in:

  8. Search for Hisakazu Yamagishi in:

  9. Search for Dietrich Keppler in:

  10. Search for Shoichiro Tsukita in:

  11. Search for Sachiko Tsukita in:

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sachiko Tsukita.

About this article

Publication history






Further reading