bims-apauto 2023-04-30 papers

Issue of 2023–04–30
three papers selected by
Su Hyun Lee, Harvard University

Mol Cell. 2023 Apr 18. pii: S1097-2765(23)00244-7. [Epub ahead of print]

Chaperone-directed ribosome repair after oxidative damage.

Yoon-Mo Yang, Youngeun Jung, Daniel Abegg, Alexander Adibekian, Kate S Carroll, Katrin Karbstein.

Because of the central role ribosomes play for protein translation and ribosome-mediated mRNA and protein quality control (RQC), the ribosome pool is surveyed and dysfunctional ribosomes degraded both during assembly, as well as the functional cycle. Oxidative stress downregulates translation and damages mRNAs and ribosomal proteins (RPs). Although damaged mRNAs are detected and degraded via RQC, how cells mitigate damage to RPs is not known. Here, we show that cysteines in Rps26 and Rpl10 are readily oxidized, rendering the proteins non-functional. Oxidized Rps26 and Rpl10 are released from ribosomes by their chaperones, Tsr2 and Sqt1, and the damaged ribosomes are subsequently repaired with newly made proteins. Ablation of this pathway impairs growth, which is exacerbated under oxidative stress. These findings reveal an unanticipated mechanism for chaperone-mediated ribosome repair, augment our understanding of ribosome quality control, and explain previous observations of protein exchange in ribosomes from dendrites, with broad implications for aging and health.

Keywords: chaperone; oxidative damage; repair; ribosome

DOI: https://doi.org/10.1016/j.molcel.2023.03.030

EMBO J. 2023 Apr 27. e112799

FBXL4 ubiquitin ligase deficiency promotes mitophagy by elevating NIX levels.

Hannah Elcocks, Ailbhe J Brazel, Katy R McCarron, Manuel Kaulich, Koraljka Husnjak, Heather Mortiboys, Michael J Clague, Sylvie Urbé.

Selective autophagy of mitochondria, mitophagy, is linked to mitochondrial quality control and as such is critical to a healthy organism. We have used a CRISPR/Cas9 approach to screen human E3 ubiquitin ligases for influence on mitophagy under both basal cell culture conditions and upon acute mitochondrial depolarization. We identify two cullin-RING ligase substrate receptors, VHL and FBXL4, as the most profound negative regulators of basal mitophagy. We show that these converge, albeit via different mechanisms, on control of the mitophagy adaptors BNIP3 and BNIP3L/NIX. FBXL4 restricts NIX and BNIP3 levels via direct interaction and protein destabilization, while VHL acts through suppression of HIF1α-mediated transcription of BNIP3 and NIX. Depletion of NIX but not BNIP3 is sufficient to restore mitophagy levels. Our study contributes to an understanding of the aetiology of early-onset mitochondrial encephalomyopathy that is supported by analysis of a disease-associated mutation. We further show that the compound MLN4924, which globally interferes with cullin-RING ligase activity, is a strong inducer of mitophagy, thus providing a research tool in this context and a candidate therapeutic agent for conditions linked to mitochondrial dysfunction.

Keywords: BNIP3; FBXL4; NIX; VHL; mitophagy

DOI: https://doi.org/10.15252/embj.2022112799

Autophagy. 2023 Apr 28.

Autophagy Inhibition as a Potential Therapeutic Strategy for Breast Cancer with Mitochondrial Translation Defect Caused by CBFB-Deficiency.

Navdeep Malik, Hualong Yan, Young-Im Kim, Gamze Ayaz, Shasha Wang, Payel Mondal, Ji Luo, Jing Huang.

Autophagy plays a crucial role in tumor initiation and progression. However, targeting autophagy in cancer has proven challenging due to genetic or epigenetic factors that may affect the efficacy of autophagy inhibition. Therefore, identifying biomarkers is crucial for selecting patients who are likely to benefit from this treatment modality. We show that dysregulation of mitochondrial translation caused by CBFB (core-binding factor subunit beta) deficiency can sensitize the tumors to autophagy inhibition. CBFB and its binding partner HNRNPK (heterogeneous nuclear ribonucleoprotein K) interact with mRNAs encoded by the mitochondrial genome (mt-mRNAs) and maintain their translation. Specifically, CBFB enhances the binding of TUFM (Tu translation elongation factor, mitochondrial), an elongation factor for mitochondrial translation, to mt-mRNAs. CBFB deficiency, which often occurs in estrogen receptor-positive breast tumors, results in elevated autophagy and mitophagy that promote cancer cell survival. Consequently, these cells are hypersensitive to autophagy inhibition, creating a targetable vulnerability. Studies using in vivo models have shown that inhibiting autophagy selectively eliminates breast tumor cells with mitochondrial translation defects resulting from CBFB deficiency. Our results suggest that autophagy inhibition may be an effective treatment option for breast tumors carrying CBFB alterations.

Keywords: Autophagy; CBFB; PIK3CA; autophagy in cancer; autophagy targeting; breast cancer; mitochondria; mitochondrial translation; mitophagy

DOI: https://doi.org/10.1080/15548627.2023.2208481