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Q. Bian, A. F. Fernandes, A. Taylor, M. Wu, P. Pereira, F. Shang; Expression of K6W-Ubiquitin in Lens Epithelial Cells Leads to Up-Regulation of a Broad Spetrum of Molecular Chaperones. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4503. doi: https://doi.org/.
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Accumulation and precipitation of abnormal proteins are associated with many age-related diseases. The ubiquitin-proteasome pathway (UPP) is one of the protein quality control mechanisms that selectively degrade damaged or obsolete proteins. The other arm of the protein quality control mechanism is molecular chaperones, which bind to and help refold unfolded or misfolded proteins. We previously showed that the molecular chaperones and the UPP work in a competitive manner in eliminating the denatured proteins. To further investigate the interaction between the two protein quality control mechanisms, we determined the effects of impairment of the UPP on the expression of molecular chaperones in human lens epithelial cells (HLEC).
K6W-ubiquitin, a dominant negative inhibitor of the UPP, was expressed in confluent HLEC via an adenoviral vector. The mRNA levels of cytoplasmic and endoplasmic reticulum (ER) chaperones were determined by Real-Time RT-PCR. Protein levels for these chaperones were determined by Western blotting.
Expression of K6W-ubiquitin impeded the UPP-mediated proteolysis and resulted in accumulation of damaged proteins in the cells. Expression of K6W-ubiquitin in HLEC also increased the expression of a broad spectrum of molecular chaperones. Among the heat-shock proteins, mRNA for αB-crystallin, Hsp70 and Hsp90 increased 27-fold, 21-fold and 2-fold, respectively, in response to expression of K6W-ubiquitin. Among the ER chaperones and ER-stress related factors, mRNA levels of protein disulfide isomerase ,Grp75, Grp78, Grp94, and CHOP increased from 1.7-fold to 3.7-fold. The mRNA for Hsp60 also increased 1.6 fold in response to expression of K6W-ubiquitin. The expression pattern of these chaperones in response to expression of K6W ubiquitin is similar to that when cells were treated with proteasome inhibitors or heat-shock.
It appears that up-regulation of these chaperones is related to the elevated levels of abnormal proteins in the cells. These findings support our hypothesis that the molecular chaperones and the UPP may back each other up in the process of protein quality control. The up-regulation of molecular chaperones in response to expression of dominant negative ubiquitin may compensate for the impairment of the UPP in degradation of abnormal proteins.
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