R. Brian Doctor Assistant Professor Medicine / Cell and Developmental Biology Ph.D., Duke University, 1993 Gastroenterology and Hepatology BRB Room 733H UCHSC, Box B158 4200 East 9th Ave. Denver, CO 80262 Phone: 303-315-8567 Fax: 303-315-5711 Email: Brian.Doctor@UCHSC.edu

Membrane-cytoskeleton linking proteins in epithelial function and disease

Research in my laboratory is focused on understanding the role of the actin cytoskeleton and cytoskeleton-associated proteins in directing epithelial functions in normal and diseased tissues. Our model epithelium is the intrahepatic bile duct. This epithelium is comprised of a single layer of cholangiocytes. These cells are hormonally regulated to dilute and alkalinize the bile through the secretion of bicarbonate-rich fluid and are the specific site of injury in a number of cholestatic liver diseases. Our two main projects are:
(1) understanding the mechanisms by which actin-associated proteins moderate secretion from the intrahepatic bile duct under physiologic conditions, and
(2) understanding the causation of the errant growth and secretion that is responsible for liver cysts in ADPKD liver disease.

Actin cytoskeleton and bile duct secretion
Ductular secretion is initiated by secretion of Cl- from cholangiocytes. The cAMP-dependent CFTR Cl- channel is a primary Cl- channel responsible for this regulated movement of ions and water. The distrbution and function of CFTR is moderated by its cytoskeletal association via the proteins Ezrin and ERM Binding Phosphoprotein 50 (EBP50). Previously we showed using a dominant negative approach in cultured cholangiocytes that EBP50 was essential for cAMP activation of Cl- secretion. Furthermore, we demonstrated EBP50 is capable of self-associating through interactions of specific domains within the EBP50 protein. Ongoing projects include determining (a) how EBP50 self-association is regulated through phosphorylation and (b) the functional ramifications of EBP50 self-association on cholangiocyte secretion. These studies utilize cultured cholangiocyte models and apply a variety of cellular, molecular and biochemical techniques.

Errant growth and secretion in ADPKD liver cysts
Autosomal dominant polycystic kidney disease (ADPKD) is a highly prevalent (~1 in 1,000 live births) genetic disease that results in significant morbidity and mortality by the fifth decade of life. The liver is the second most affected organ and manifestations from concurrent liver cyst disease accounts for up to 10% of the complications that arise in patients with advanced ADPKD. The intrahepatic bile duct is the exclusive site of genesis of liver cysts. The goals for the near future include developing animal and cellular models of ADPKD liver cyst disease and apply these models to the mechanistic understanding of the errant growth and secretion in liver cyst epithelia. Important clues are being uncovered in the analysis of liver cyst fluid and epithelia recovered from ADPKD surgical patients. Identification of important secretagogues, growth factors and cytokines will subsequently be used to direct more mechanistic studies in animal and cell culture models. It is hoped that a mechanistic understanding of the disease will result in the development of pharmacologic therapies that specifically intervene in the formation or progression of ADPKD liver cysts.

Selected Publications

Doctor RB, Fouassier L. Emerging roles of the actin cytoskeleton in cholangiocyte function and disease. Semin Liver Dis. 2002 Aug;22(3):263-76.

Doctor RB, Dahl R, Fouassier L, Kilic G, Fitz JG. Cholangiocytes exhibit dynamic, actin-dependent apical membrane turnover. Am J Physiol Cell Physiol. 2002 May;282(5):C1042-52.

Kilic G, Doctor RB, Fitz JG. Insulin stimulates membrane conductance in a liver cell line: evidence for insertion of ion channels through a phosphoinositide 3-kinase-dependent mechanism. J Biol Chem. 2001 Jul 20;276(29):26762-8.

Roman RM, Smith RL, Feranchak AP, Clayton GH, Doctor RB, Fitz JG. ClC-2 chloride channels contribute to HTC cell volume homeostasis. Am J Physiol Gastrointest Liver Physiol. 2001 Mar;280(3):G344-53.

Fouassier L, Duan CY, Feranchak AP, Yun CH, Sutherland E, Simon F, Fitz JG, Doctor RB. Ezrin-radixin-moesin-binding phosphoprotein 50 is expressed at the apical membrane of rat liver epithelia. Hepatology. 2001 Jan;33(1):166-76.

Latest Publications in PubMed