Transglutaminase participates in UVB-induced cell death pathways in human corneal epithelial cells.
OBJECTIVE
Ultraviolet light (UVB) is known to cause apoptosis in human corneal epithelial cells. This study evaluates the role of transglutaminase in regulating tumor necrosis factor (TNF) receptor clustering as well as caspase activation in UVB-induced apoptosis in human corneal epithelial cells.


METHODS
A human corneal epithelial cell line was used. A single dose of UVB (20 mJ/cm2) was used as a stimulus. Cell viability and cell death were investigated by MTT, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL), and caspase-3 assays. Immunofluorescent staining was used to investigate TNF receptor-I clustering at various time intervals after UVB. Short interfering RNA was used to knock down transglutaminase-2 expression. Fluorescein-cadaverine uptake was used to assess transglutaminase activity. A noncovalent peptide delivery system was used to transfect guinea pig liver transglutaminase into corneal epithelial cells.


RESULTS
UVB increased transglutaminase activity, reduced cell viability, and increased TUNEL staining. UVB or TNF-alpha promoted TNF-receptor-I clustering, a process inhibited by the transglutaminase inhibitor, mono-dansyl cadaverine. UVB also increased activated caspase-3, in a manner suppressible by mono-dansyl cadaverine. Intracellular delivery of exogenous transglutaminase markedly increase caspase-3 activation compared with the vehicle control.


CONCLUSIONS
Transglutaminase enzymatic activity is involved in corneal epithelial cell death after UVB and appears to participate in two steps regulating this process, clustering of TNF receptor-I and caspase-3 activation.
Tong
Louis
L
Ocular Surface Center, Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030, USA.
Chen
Zhuo
Z
De Paiva
Cintia S
CS
Beuerman
Roger
R
Li
De-Quan
DQ
Pflugfelder
Stephen C
SC
D017209:Apoptosis / Q000528:radiation effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D019573:Epithelium, Corneal / Q000187:drug effects / Q000201:enzymology* / Q000528:radiation effects*; D019084:Fluorescent Antibody Technique, Indirect; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D020287:In Situ Nick-End Labeling; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D034741:RNA, Small Interfering / Q000494:pharmacology; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D011503:Transglutaminases / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014466:Ultraviolet Rays
D034741:RNA, Small Interfering; D047888:Receptors, Tumor Necrosis Factor, Type I; D014409:Tumor Necrosis Factor-alpha; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D019204:GTP-Binding Proteins