Altered phenotype of cultured urothelial and other stratified epithelial cells: implications for wound healing

Abstract

Sun, Tung-Tien. Altered phenotype of cultured urothelial and other stratified epithelial cells: implications for wound healing. Am J Physiol Renal Physiol 291: F9 -F21, 2006; doi:10.1152/ajprenal.00035.2006.-The differentiation of cultured stratified epithelial cells can deviate significantly from that of normal epithelium, leading to suggestions that cultured cells undergo abnormal differentiation, or a truncated differentiation. Thus cultured epidermal and corneal epithelial cells stop synthesizing their tissue-specific keratin pair K1/K10 and K3/K12, respectively. The replacement of these keratins in the suprabasal compartment by K6/K16 keratins that are made by all stratified squamous epithelia during hyperplasia rules out a truncated differentiation. Importantly, the keratin pattern of in vivo corneal epithelium undergoing wound repair mimics that of cultured rabbit corneal epithelial cells. Although cultured urothelial cells continue to synthesize uroplakins, which normally form two-dimensional crystalline urothelial plaques covering almost the entire apical urothelial surface, these proteins do not assemble into crystals in cultured cells. Cultured epithelial cells can, however, rapidly regain normal differentiation on the removal of mitogenic stimuli, the use of a suitable extracellular matrix, or the transplantation of the cells to an in vivo, nonmitogenic environment. These data suggest that cultured epithelial cells adopt altered differentiation patterns mimicking in vivo regenerating or hyperplastic epithelia. Blocking the synthesis of tissue-specific differentiation products, such as the K1 and K10 keratins designed to form extensive disulfide cross-links in cornified cells, or the assembly of uroplakin plaques allows epithelial cells to better migrate and proliferate, activities that are of overriding importance during wound repair. Cultured urothelial and other stratified epithelial cells provide excellent models for studying the regulation of the synthesis and assembly of differentiation products, a key cellular process during epithelial wound repair. bladder epithelium; uroplakin; urothelial plaque; permeability barrier THE ABILITY TO GROW CELLS of stratified squamous epithelia and to reproduce their in vivo differentiation program under welldefined in vitro conditions can greatly facilitate the study of the growth and differentiation of these cell types. Thus the in vitro cultivation of human epidermal cells using lethally irradiated or mitomycin-treated 3T3 feeder cells (80) made possible early breakthroughs in studying the synthesis of keratins (23,24,97,98) and the formation of cornified envelope (83,84,95), and for using in vitro expanded epidermal cells to treat burn patients (21,25). Studies of the differentiation of cultured corneal epithelial cells led to the discovery that corneal epithelial stem cells reside in the basal cell layer of peripheral corneal epithelium in a previously ignored area called the limbus (87) and to the use of cultured corneal epithelial cells in restoring patie...

Persistent uroplakin expression in advanced urothelial carcinomas: implications in urothelial tumor progression and clinical outcome

“…In UP knockout mice, the loss of UPII or UPIII leads to a dramatic reduction of their natural partners, UPIa or UPIb, respectively (18). This is consistent with the fact that singly transfected UPs in cultured cells cannot exit efficiently from the endoplasmic reticulum, thus being rapidly degraded (17,22). Thus, the coordinated expression of UPs and their proper post-synthetic assembly may play a critical role in UP stability and immunohistochemical detectability.…”

“…Alternatively, absence of UP expression could occur on a protein level as a result of specific defects in UP assembly, as has been suggested from studies of cultured normal urothelial cells and UP knockout mice. For example, cultured bovine urothelial cells synthesize large amounts of UP mRNAs without making corresponding amounts of UP proteins, probably due to the lack of cytoplasmic vesicles that would otherwise allow UPs to be assembled into two-dimensional crystals (22). In UP knockout mice, the loss of UPII or UPIII leads to a dramatic reduction of their natural partners, UPIa or UPIb, respectively (18).…”

“…This was proven to be the case in cultured normal urothelial cells, where incomplete differentiation and/or hyper-proliferation led to a profound reduction of all UPs, particularly on a protein level (22). Similarly, in a number of human bladder cancer cell lines, UPs are either down-regulated (RT4, RT112) or undetectable (J82, T24) (23) [unpublished observation].…”

Reviewing Interstitial Cystitis Models and Treatments: A Focus on the Urothelium

“…of a complex and balanced process involving migration, proliferation and differentiation, influenced by a range of factor including epithelial growth factor (EGF), platelet derived growth factor (PDGF), as well as retinoic acid (RA) (15). The structural and functional integrity of the urothelium is supported by intracellular protein complexes called tight junctions.…”

“…Its integrity is maintained as result of an equilibrated process of migration, proliferation and differentiation (15). Tight junctions contribute to the urothelial barrier function, among those sealing proteins are the occludins, claudins as well as uroplakins (15,16).…”