Autophagy deficiency activates rDNA transcription

ABSTRACT

Macroautophagy/autophagy, a highly conserved lysosome-dependent degradation pathway, has been intensively studied in regulating cell metabolism by degradation of intracellular components. In this study, we link autophagy to RNA metabolism by uncovering a regulatory role of autophagy in ribosomal RNA (rRNA) synthesis. Autophagy-deficient cells exhibit much higher 47S precursor rRNA level, which is caused by the accumulation of SQSTM1/p62 (sequestosome 1) but not other autophagy receptors. Mechanistically, SQSTM1 accumulation potentiates the activation of MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) signaling and promotes the assembly of RNA polymerase I pre-initiation complex at ribosomal DNA (rDNA) promoters, which leads to an increase of 47S rRNA transcribed from rDNA. Functionally, autophagy deficiency promotes protein synthesis, cell growth and cell proliferation, both of which are dependent on SQSTM1 accumulation. Taken together, our findings suggest that autophagy deficiency is involved in RNA metabolism by activating rDNA transcription and provide novel mechanisms for the reprogramming of cell metabolism in autophagy-related diseases including multiple types of cancers.

Abbreviations: 5-FUrd: 5-fluorouridine; AMPK: AMP-activated protein kinase; ATG: autophagy related; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; ChIP: chromatin immunoprecipitation; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAPK/ERK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; NBR1: NBR1 autophagy cargo receptor; NFKB/NF-κB: nuclear factor kappa B; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; OPTN: optineurin; PIC: pre-initiation complex; POLR1: RNA polymerase I; POLR1A/RPA194: RNA polymerase I subunit A; POLR2A: RNA polymerase II subunit A; rDNA: ribosomal DNA; RPS6KB1/S6K1: ribosomal protein S6 kinase B1; rRNA: ribosomal RNA; RUBCN/Rubicon: rubicon autophagy regulator; SQSTM1/p62: sequestosome 1; STX17: syntaxin 17; SUnSET: surface sensing of translation; TAX1BP1: Tax1 binding protein 1; UBTF/UBF1: upstream binding transcription factor; WIPI2: WD repeat domain, phosphoinositide interacting 2; WT: wild-type.

KEYWORDS:

• Autophagy
• MTORC1
• rDNA
• rRNA
• SQSTM1/p62

Acknowledgments

We are grateful to the Imaging Center of Zhejiang University School of Medicine for their assistance in confocal microscopy. We thank Dr. Han-Ming Shen (National University of Singapore Yong Loo Lin School of Medicine, Singapore), Dr. Feng Shao (National Institute of Biological Sciences, Beijing, China), and Dr. Qiming Sun (Zhejiang University School of Medicine, Hangzhou, China) for kindly providing cell lines and reagents.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This study was supported by the Training Program for Excellent Young Innovators of Changsha [kq2009021]; the National Natural Science Foundation of China [31970694]; the Young Elite Scientists Sponsorship Program by China Association for Science and Technology (CAST) [2019QNRC001]; and the Chao Kuang Piu High-tech Development Fund [2020QN024].