Defining a link between gap junction communication, proteolysis, and cataract formation.
Disruption of the connexin alpha 3 (Cx46) gene (alpha 3 (-/-)) in mice results in severe cataracts within the nuclear portion of the lens. These cataracts are associated with proteolytic processing of the abundant lens protein gamma-crystallin, leading to its aggregation and subsequent opacification of the lens. The general cysteine protease inhibitor, E-64, blocked cataract formation and gamma-crystallin cleavage in alpha 3 (-/-) lenses. Using a new class of activity-based cysteine protease affinity probes, we identified the calcium-dependent proteases, m-calpain and Lp82, as the primary targets of E-64 in the lens. Profiling changes in protease activities throughout cataractogenesis indicated that Lp82 activity was dramatically increased in alpha 3 (-/-) lenses and correlated both spatially and temporally with cataract formation. Increased Lp82 activity was due to calcium accumulation as a result of increased influx and decreased outflux of calcium ions in alpha 3 (-/-) lenses. These data establish a role for alpha 3 gap junctions in maintaining calcium homeostasis that in turn is required to control activity of the calcium-dependent cysteine protease Lp82, shown here to be a key initiator of the process of cataractogenesis.
Baruch
A
A
Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143, USA.
Greenbaum
D
D
Levy
E T
ET
Nielsen
P A
PA
Gilula
N B
NB
Kumar
N M
NM
Bogyo
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002386:Cataract / Q000235:genetics / Q000473:pathology / Q000503:physiopathology* / Q000517:prevention & control; D002450:Cell Communication / Q000502:physiology*; D017630:Connexins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D017629:Gap Junctions / Q000502:physiology*; D007908:Lens, Crystalline / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D009924:Organ Culture Techniques
D017630:Connexins; D015853:Cysteine Proteinase Inhibitors; C082917:GJA3 protein, human; D002154:Calpain; D003546:Cysteine Endopeptidases; C118624:calpain Lp82; D007930:Leucine; C024974:E 64; D002118:Calcium