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Identification of long-lived proteins retained in cells undergoing repeated asymmetric divisions
Contributed by Daniel E. Gottschling, August 20, 2014 (sent for review July 11, 2014; reviewed by Edward M. Marcotte and Vladimir Denic)
See related content:
- Profile of Daniel E. Gottschling- Sep 22, 2014

Significance
Long-lived proteins in extracellular spaces (joints/tissues) or within specialized nondividing cells (eye-lens) are associated with age-related decline. However, aging also occurs in dividing stem cells. Although several hypotheses have been proposed to explain how stem cells age, none have addressed whether long-lived proteins contribute to aging, partially because of technical challenges in identifying such proteins. We developed a method to overcome these limitations in the model system Saccharomyces cerevisiae. We identified two classes of long-lived asymmetrically retained proteins (LARPs). Full-length LARPs remain intact throughout the mother cell lifespan and accumulate in abundance or become posttranslationally modified. Fragmented LARPs are original proteins that are partially degraded, yet retained by the mother cell during aging. We speculate that LARPs contribute to the aging process.
Abstract
Long-lived proteins have been implicated in age-associated decline in metazoa, but they have only been identified in extracellular matrices or postmitotic cells. However, the aging process also occurs in dividing cells undergoing repeated asymmetric divisions. It was not clear whether long-lived proteins exist in asymmetrically dividing cells or whether they are involved in aging. Here we identify long-lived proteins in dividing cells during aging using the budding yeast, Saccharomyces cerevisiae. Yeast mother cells undergo a limited number of asymmetric divisions that define replicative lifespan. We used stable-isotope pulse-chase and total proteome mass-spectrometry to identify proteins that were both long-lived and retained in aging mother cells after ∼18 cells divisions. We identified ∼135 proteins that we designate as long-lived asymmetrically retained proteins (LARPS). Surprisingly, the majority of LARPs appeared to be stable fragments of their original full-length protein. However, 15% of LARPs were full-length proteins and we confirmed several candidates to be long-lived and retained in mother cells by time-lapse microscopy. Some LARPs localized to the plasma membrane and remained robustly in the mother cell upon cell division. Other full-length LARPs were assembled into large cytoplasmic structures that had a strong bias to remain in mother cells. We identified age-associated changes to LARPs that include an increase in their levels during aging because of their continued synthesis, which is not balanced by turnover. Additionally, several LARPs were posttranslationally modified during aging. We suggest that LARPs contribute to age-associated phenotypes and likely exist in other organisms.
Footnotes
↵1N.H.T. and C.K.L contributed equally to this work.
- ↵2To whom correspondence should be addressed. Email: dgottsch{at}fhcrc.org.
This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected in 2011.
Author contributions: N.H.T., C.K.L., Z.W.N., K.A.H., P.R.G., J.J.H., and D.E.G. designed research; N.H.T., C.K.L., Z.W.N., K.A.H., P.R.G., J.J.H., and D.E.G. performed research; M.P.F. analyzed data; and N.H.T., C.K.L., and D.E.G. wrote the paper.
Reviewers: E.M.M., University of Texas at Austin; and V.D., Harvard University.
The authors declare no conflict of interest.
Data deposition: Mass spectrometry data have been deposited in the ProteomeXchange Consortium (http://proteomecentral.proteomexchange.org) with the dataset identifier PXD001251.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1416079111/-/DCSupplemental.