title: Developmental truncations of connexin 50 by caspases adaptively regulate gap junctions/hemichannels and protect lens cells against ultraviolet radiation.
abstract: The gap junction-forming connexin (Cx) 50 is truncated gradually during lens development. Premature cleavage of lens connexins is thought to be associated with cataract formation. We have shown previously that Cx50 is likely to be cleaved by caspase-3 like protease during chick lens development. Here, using HPLC-electrospray tandem mass spectrometry, we mapped two cleavage sites at the C terminus of Cx50 after Glu-368 and Asp-379 and identified caspase-3 and caspase-1 as the responsible proteases, respectively. The activity of caspase-1, like caspase-3, was detected in the outer cortex increased during lens development, which coincided with the accumulation of the truncated fragments of Cx50 in the core region of the lens. The truncated Cx50 fragments present in older lenses were reproduced in the younger lens after treatment with UV radiation; this cleavage could be partially blocked by caspase-1/3-specific inhibitors. Interestingly, as compared with full-length Cx50, caspase-truncated Cx50 showed a dramatic decrease in gap junction coupling and a loss of hemichannel function. Furthermore, expression of caspase-truncated Cx50 fragments increased cell viability against UV radiation as compared with full-length Cx50. Together, these results suggest that both caspase-1 and -3 are responsible for the cleavage at the C terminus of Cx50 during lens development. The reduction of gap junction coupling and closure of hemichannels formed by truncated Cx50 are likely to adaptively protect cells against elevated oxidative stress associated with lens aging.
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, College of Life Sciences, Nanjing University, Nanjing 210093, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Wang
authors.forename: Sumin
authors.initials: S
authors.lastname: Gu
authors.forename: Xinye
authors.initials: X
authors.lastname: Yin
authors.forename: Susan T
authors.initials: ST
authors.lastname: Weintraub
authors.forename: Zichun
authors.initials: Z
authors.lastname: Hua
authors.forename: Jean X
authors.initials: JX
authors.lastname: Jiang
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D020170:Caspase 1 / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism / Q000528:radiation effects; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism* / Q000528:radiation effects; D015151:Immunoblotting; D007473:Ion Channels / Q000378:metabolism; D007908:Lens, Crystalline / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D009154:Mutation; D059748:Proteolysis; D013997:Time Factors; D014466:Ultraviolet Rays; D000099264:Connexin 50
chemical_list: D001224:Aspartic Acid; D020170:Caspase 1; D053148:Caspase 3; D020169:Caspases; D017630:Connexins; D005136:Eye Proteins; D007473:Ion Channels; D000099264:Connexin 50