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Irie T, Benson NC, French SW: Electron microscopic study of the in vitro calcium-dependent degradation of Mallory bodies and intermediate filaments in hepatocytes. Exp Mol Pathol. 2006 Aug;81(1):8-14. Epub 2006 May 24.
Isolated crude fractions of intermediate filaments (IFs) from livers of control and griseofulvin-fed mice were incubated with calcium (Ca2+) or ethylene glycol bis (beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA). The fractions were semiquantitatively compared using electron microscopy to study the Ca2+-dependent degradation of Mallory bodies and IFs. Numerous intermediate filaments were observed in the cell cortex and cytoplasm of hepatocytes both in control and griseofulvin-fed mice at zero time and after incubation in EGTA. However, only rare IFs near desmosomes were seen after incubation with Ca2+ in the fractions from two control mice. In the remaining controls no IFs survived incubation with Ca2+. Although almost all IFs disappeared after incubation with Ca2+ in griseofulvin-fed mice, some IFs could be detected near desmosomes in all cases. In contrast, Mallory bodies were observed to survive both Ca2+ and EGTA incubations. There was no morphologic difference between the Mallory bodies incubated in Ca2+ or EGTA. The disappearance of IFs after incubation in Ca2+ indicates that the IF's protein of hepatocytes (cytokeratin) can not retain its filamentous structure in the presence of Ca2+. This suggests that Ca2+-dependent factor (s) may regulate IF's degradation. Whether the protein subunits of the IFs were chemically altered was not determined. The resistance of Mallory bodies to Ca2+ dependent degradation suggests that they may form in part as a result of an imbalance in the rate of filament formation and degradation favoring growth of the Mallory body filaments. |
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