RESUMO
We examined the cellular localization of nine different connexin32 (Cx32) mutants associated with X-linked Charcot-Marie-Tooth disease (CMTX) in communication-incompetent mammalian cells. Cx32 mRNA was made, but little or no protein was detected in one class of mutants. In another class of mutants, Cx32 protein was detectable in the cytoplasm and at the cell surface, where it appeared as plaques and punctate staining. Cx32 immunoreactivity in a third class of mutants was restricted to the cytoplasm, where it often colocalized with the Golgi apparatus. Our studies suggest that CMTX mutations have a predominant effect on the trafficking of Cx32 protein, resulting in a potentially toxic cytoplasmic accumulation of Cx32 in these cells. These results and evidence of cytoplasmic accumulation of other mutated myelin proteins suggest that diseases affecting myelinating cells may share a common pathophysiology.
Assuntos
Doença de Charcot-Marie-Tooth/metabolismo , Conexinas/metabolismo , Sequência de Aminoácidos , Transporte Biológico , Células Cultivadas , Doença de Charcot-Marie-Tooth/genética , Conexinas/genética , Citoplasma/metabolismo , Regulação da Expressão Gênica , Complexo de Golgi/metabolismo , Humanos , Dados de Sequência Molecular , Fenótipo , Mutação Puntual , Proteínas Recombinantes de Fusão/metabolismo , Deleção de Sequência , Proteína beta-1 de Junções ComunicantesRESUMO
IDDM in humans and STZ-induced diabetes in rats are both characterized in the early phase of the disease by glomerular hypertrophy; and, in the chronic phase of the disease, by mesangial expansion and glomerular basement membrane thickening. Decreases in glomerular intracellular protein degradation rates in diabetic individuals could contribute to the glomerular hypertrophy by allowing a build-up of cellular protein. Decreases in extracellular protease activity could contribute to the build-up of matrix protein in the mesangium and glomerular basement membrane. In this study, the levels of lysosomal cathepsin activities and glomerular metalloprotease activities were measured in isolated glomerular homogenates from STZ-induced diabetic rats at 4 days and 5 wk after administration of the drug. Some of the rats in the 5-wk study were treated with daily insulin; others were untreated. After 4 days of diabetes, cathepsin B and L activities were decreased by 15-45% when correlated with the levels of glomerular protein or DNA. Glomerular metalloprotease activity was decreased by 75% in the diabetic rats when compared with controls. After 5 wk of diabetes, cathepsin activities either were unchanged (for cathepsin B and L together or cathepsin S) or increased (cathepsin B alone) in insulin-treated diabetic rats, and continued to be decreased in untreated diabetic rats. A 40-50% decrease in glomerular metalloprotease activity continued in both diabetic groups. These data strongly suggest that decreases in the lysosomal cathepsin activities may contribute to IDDM-induced glomerular cellular hypertrophy. The data further indicate that a decrease in glomerular metalloprotease activity may contribute to diabetes-induced mesangial expansion and glomerular basement membrane thickening.(ABSTRACT TRUNCATED AT 250 WORDS)
