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A role for Rad23 proteins in 26S proteasome-dependent protein degradation?
Theo van Laar1, Alex J van der Eb, Carrol Terleth
1MGC Department of Radiation Genetics and Chemical Mutagenesis, Leiden University Medical Centre, P.O. Box 9503, 2300 RA Leiden, The Netherlands. t.van_laar@lumc.nl
Abstract:
Treatment of cells with genotoxic agents affects protein degradation in both positive and negative ways. Exposure of S. cerevisiae to the alkylating agent MMS resulted in activation of genes that are involved in ubiquitin- and 26S proteasome-dependent protein degradation. This process partially overlaps with the activation of the ER-associated protein degradation pathway. The DNA repair protein Rad23p and its mammalian homologues have been shown to inhibit degradation of specific substrates in response to DNA damage. Particularly the recently identified inhibition of degradation by mouse Rad23 protein (mHR23) of the associated nucleotide excision repair protein XPC was shown to stimulate DNA repair.Recently, it was shown that Rad23p and the mouse homologue mHR23B also associate with Png1p, a deglycosylation enzyme. Png1p-mediated deglycosylation plays a role in ER-associated protein degradation after accumulation of malfolded proteins in the endoplasmic reticulum. Thus, if stabilization of proteins that are associated with the C-terminus of Rad23p is a general phenomenon, then Rad23 might be implicated in the stimulation of ER-associated protein degradation as well. Interestingly, the recently identified HHR23-like protein Mif1 is also thought to play a role in ER-associated protein degradation. The MIF1 gene is strongly activated in response to ER-stress. Mif1 contains a ubiquitin-like domain which is most probably involved in binding to S5a, a subunit of the 19S regulatory complex of the 26S proteasome. On the basis of its localization in the ER-membrane, it is hypothesized that Mif1 could play a role in the translocation of the 26S proteasome towards the ER-membrane, thereby enhancing ER-associated protein degradation.
Insights
Genotoxic agents impact protein degradation pathways. Rad23 and Mif1 proteins are implicated in stimulating DNA repair and ER-associated protein degradation, respectively.
Area of Science:
- Cellular biology
- Molecular biology
- Biochemistry
Background:
- Genotoxic agents influence protein degradation, affecting cellular homeostasis.
- Rad23p and its mammalian homologs (e.g., mHR23) are involved in DNA repair and protein degradation.
- ER-associated protein degradation (ERAD) pathways handle misfolded proteins in the endoplasmic reticulum.
Purpose of the Study:
- To investigate the role of Rad23p and related proteins in protein degradation pathways.
- To explore the connection between DNA repair, ERAD, and the proteins Rad23p and Mif1.
- To understand how genotoxic stress impacts ubiquitin- and proteasome-dependent degradation.
Main Methods:
- Exposure of Saccharomyces cerevisiae to the methyl methanesulfonate (MMS) alkylating agent.
- Analysis of gene expression changes related to ubiquitin- and 26S proteasome-dependent protein degradation.
- Investigating protein-protein interactions involving Rad23p, mHR23B, Png1p, and Mif1.
- Examining the role of Mif1 in ER-associated protein degradation and proteasome localization.
Main Results:
- MMS exposure activated genes involved in ubiquitin- and 26S proteasome-dependent protein degradation in S. cerevisiae.
- This activation partially overlapped with the ER-associated protein degradation pathway.
- Rad23p and mHR23 inhibit degradation of specific substrates, stimulating DNA repair.
- Rad23p and mHR23B associate with Png1p, a deglycosylation enzyme involved in ERAD.
- Mif1, a HHR23-like protein, is strongly activated by ER-stress and hypothesized to enhance ERAD by facilitating proteasome translocation.
Conclusions:
- Rad23 proteins may play a role in stimulating ER-associated protein degradation.
- Mif1 is implicated in ER-associated protein degradation, potentially by recruiting the 26S proteasome to the ER membrane.
- Cellular responses to genotoxic stress involve complex interplay between DNA repair and protein degradation pathways.