Proteasome inhibitor ‐induced protein aggregation is regulated via HSP90, HDACs and microtubulus stability in ARPE‐19 cells

• Published in: Acta ophthalmologica (Oxford, England) Vol. 87; no. s244
• Main Authors: KAARNIRANTA, K, RYHäNEN, T, VIIRI, J, UUSITALO, H, SALMINEN, A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-09-2009
• ISSN: 1755-375X; 1755-3768
• DOI: 10.1111/j.1755-3768.2009.215.x

Purpose Impaired degradation of cellular proteins is implicated in aged RPE cells. In addition to lysosomal protein clearance, many cellular proteins are degradated in proteasomes. Heat shock proteins (HSPs) tend to prevent the accumulation of cytotoxic protein aggregates. Regulatory role of HSPs, histone deacetylases (HDACs) and tubulin stability state in proteasome inhibitor ‐induced protein aggregation in ARPE–19 cells were evaluated.
Methods HSP90, HSP70, HSC70, HSP27, ubiquitin and acetylated tubulin expression levels were analyzed by Western blotting. Phase contrast and transmission electron microscopy and immunofluorescence analysis were used to detect cellular organelles and to evaluate morphological changes.
Results Western blotting analysis showed increased HSP70 expression levels in response to HSP90 inhibitor geldanamycin (GA) and proteasome inhibitor MG‐132. Trichostatin A(HDAC inhibitor) and taxol evoked increased acetylation level of tubulin. Interestingly, MG‐132 ‐induced juxtranuclear protein aggregates were not formed in response to GA, while during taxol treatment aggregation process was conventional. During trichostatin A and nocodazole treatment the aggregates were localized to periphery of cytoplasm rather than to juxtanuclear position. The HSP90 could not be seen together with the aggregates, while the HSP70 stained strongly with the observed juxtanuclear aggregates.
Conclusion HSP90, HDACs and tubulin polymerization state are critical regulators of proteasome inhibitor –induced protein aggregates in ARPE‐19 cells. However, total acetylation level of tubulin does not seem to be essential in the aggregation process.