Defining a link between gap junction communication, proteolysis, and cataract formation.

Abstract

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.

• Authors: A Baruch, D Greenbaum, E T Levy, P A Nielsen, N B Gilula, N M Kumar, M Bogyo
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 276 Issue 31 Pg. 28999-9006 (Aug 03 2001) ISSN: 0021-9258 [Print] United States
• PMID: 11395508 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Connexins
• Cysteine Proteinase Inhibitors
• connexin 46
• Calpain
• Cysteine Endopeptidases
• calpain Lp82
• Leucine
• E 64
• Calcium

Topics

• Animals
• Calcium (metabolism)
• Calpain (metabolism)
• Cataract (genetics, pathology, physiopathology, prevention & control)
• Cell Communication (physiology)
• Connexins (deficiency, genetics, physiology)
• Cysteine Endopeptidases (metabolism)
• Cysteine Proteinase Inhibitors (pharmacology)
• Gap Junctions (physiology)
• Lens, Crystalline (drug effects, pathology, physiology)
• Leucine (analogs & derivatives, pharmacology)
• Mice
• Mice, Inbred Strains
• Mice, Knockout
• Organ Culture Techniques