Tung-Tien Sun

sunDepartment of Urology

Research Overview

Lab Mission

The mission of the Sun laboratory is to better understand the structure and function of epithelial cells, which line the surface of various organs and are responsible for many important biological functions, including secretion, absorption, and protection. As the first line of defense in frequent contact with environmental carcinogens, epithelium-derived neoplasms (carcinomas) account for over 90% of all human tumors.


Over the past 20 years, the group has focused its attention on urothelium, which lines the entire lower urinary tract, including renal pelvis, ureters, bladder and proximal urethra. The Sun laboratory identified a group of urothelial membrane proteins, called uroplakins, that are made by mammalian bladder urothelium as major differentiation products. These uroplakins form 16-nanometer particles that are packed hexagonally, forming two-dimensional crystals (known as urothelial plaques) covering almost the entire urothelial apical surface. The Sun laboratory and collaborators have identified and characterized several uroplakin subunits and have established the following:

  • Uroplakins are integral subunits of the urothelial plaques that contribute to the remarkable permeability barrier function of the urothelium.
  • Uroplakins are useful markers for metastatic bladder cancer.
  • Uroplakin Ia may serve as the urothelial receptor for the uropathogenic E. coli which causes >90% of urinary tract infections.
  • Urinary bladder can be converted into a novel bladder bioreactor.
  • Uroplakin promoter can be used to generate transgenic models for studying the molecular pathways of bladder tumorigenesis.
  • Uroplakin defects caused by gene ablation may lead to a number of important urinary tract abnormalities, including compromised urothelial barrier function, vesicoureteral reflux, hydronephrosis and, in some cases, neonatal death.

Recent work has focused on the regulation and function of uroplakins. Specifically, Dr. Sun and colleagues would like to learn more about the detailed biological functions of uroplakins, how these proteins are assembled and targeted to the urothelial apical surface, and how are they regulated during different stages of the micturition cycle.