Project description:Cell size is tightly controlled in healthy tissues, but it is unclear how deviations in cell size affect cell physiology. To address this, we measured how the proteome changes with cell size. Protein concentration changes are widespread and predicted by subcellular localization, size-dependent mRNA concentrations, and protein turnover. As proliferating cells grow larger, concentration changes associated with cellular senescence are increasingly pronounced, suggesting that large size may be a cause rather than just a consequence of cell senescence. Consistent with this hypothesis, larger cells are prone to replicative, DNA damage-, and CDK4/6i-induced senescence. Size-dependent changes to the proteome, including those associated with senescence, are not observed when an increase in cell size is accompanied by an increase in ploidy. Together, our findings show how cell size could impact many aspects of cell physiology through remodeling the proteome and provide a rationale for cell size control and polyploidization.
Project description:Cell size is tightly controlled in healthy tissues, but it is unclear how deviations in cell size affect cell physiology. To address this, we measured how the cell's proteome changes with increasing cell size. Size-dependent protein concentration changes are widespread and predicted by subcellular localization, size-dependent mRNA concentrations, and protein turnover. As proliferating cells grow larger, concentration changes typically associated with cellular senescence are increasingly pronounced, suggesting that large size may be a cause rather than just a consequence of cell senescence. Consistent with this hypothesis, larger cells are prone to replicative, DNA-damage-induced, and CDK4/6i-induced senescence. Size-dependent changes to the proteome, including those associated with senescence, are not observed when an increase in cell size is accompanied by an increase in ploidy. Together, our findings show how cell size could impact many aspects of cell physiology by remodeling the proteome and provide a rationale for cell size control and polyploidization.
Project description:Defining the cellular factors that drive growth rate and proteome composition is essential for understanding and manipulating cellular systems. In bacteria, ribosome concentration is known to be a constraining factor of cell growth rate, while gene concentration is usually assumed not to be limiting. Here, using single-molecule tracking, quantitative single-cell microscopy, and modeling, we show that genome dilution in Escherichia coli cells arrested for DNA replication results in a decrease in the concentration of active RNA polymerases and ribosomes. The resulting sub-linear scaling of total active RNA polymerases and ribosomes with cell size leads to sub-exponential growth, even within physiological cell sizes. Cell growth rate scales proportionally with the total number of active ribosomes in a DNA concentration-dependent manner. Tandem-mass-tag mass spectrometry experiments further revealed that a decrease in DNA-to-cell-volume ratio also incrementally remodels proteome composition with cell size. Altogether, our findings indicate that genome concentration is an important driver of exponential cell growth and a global modulator of proteome composition in E. coli. Comparison with studies on eukaryotic cells suggests DNA concentration-dependent scaling principles of gene expression across domains of life.
Project description:Cellular senescence involves a stable cell cycle arrest coupled to a secretory program that, in some instances, stimulates the immune clearance of senescent cells. Using an immune competent tumor model in which senescence triggers CD8 T cell-mediated tumor rejection, we show that senescence also remodels cell surface proteome to alter how they sense environmental factors, as exemplified by Type II interferon gamma (IFN-γ). Compared to proliferating cells, senescent cells upregulate IFN-γ receptor, become hypersensitized to microenvironmental IFN-γ, and more robustly induce antigen presenting machinery -effects also recapitulated in human tumor cells treated with senescence-inducing drugs. Disruption of the IFN-γ sensing by senescent cells blunts their immune-mediated clearance without disabling their characteristic secretory program or immune cell recruitment. Our results demonstrate that senescent cells have an enhanced ability to both send and receive environmental signals, and imply that each process is required for their effective immune surveillance.
Project description:Cellular senescence involves a stable cell cycle arrest coupled to a secretory program that, in some instances, stimulates the immune clearance of senescent cells. Using an immune competent tumor model in which senescence triggers CD8 T cell-mediated tumor rejection, we show that senescence also remodels cell surface proteome to alter how they sense environmental factors, as exemplified by Type II interferon gamma (IFN-γ). Compared to proliferating cells, senescent cells upregulate IFN-γ receptor, become hypersensitized to microenvironmental IFN-γ, and more robustly induce antigen presenting machinery -effects also recapitulated in human tumor cells treated with senescence-inducing drugs. Disruption of the IFN-γ sensing by senescent cells blunts their immune-mediated clearance without disabling their characteristic secretory program or immune cell recruitment. Our results demonstrate that senescent cells have an enhanced ability to both send and receive environmental signals, and imply that each process is required for their effective immune surveillance.
Project description:Yeast cells must grow to a critical size before committing to division. It is unknown how size is measured. We find that as cells grow, mRNAs for some cell cycle activators scale faster than size, increasing in concentration, while mRNAs for some inhibitors scale slower than size, decreasing in concentration. Size-scaled gene expression could cause an increasing ratio of activators to inhibitors with size, triggering cell cycle entry. Consistent with this, expression of the CLN2 activator from the promoter of the WHI5 inhibitor, or vice versa, interfered with cell size homeostasis, yielding a broader distribution of cell sizes. We suggest that size homeostasis comes from differential scaling of gene expression with size. Such regulation of gene expression as a function of cell size could affect many cellular processes.
Project description:Unorthodox rules of extracting genetic information enable proteome expansion without increasing the genome size. The use of alternative translation initiation sites achieves this goal by allowing production of more than one protein from a single gene. Although several such examples have been serendipitously found in bacteria, genome-wide experimental mapping of alternative translation start sites has been unattainable. We found that the antibiotic retapamulin specifically arrests initiating ribosomes at start codons of the genes. Retapamulin treatment followed by Ribo-seq analysis (Ribo-RET) not only allowed mapping of conventional initiation sites at the beginning of the annotated Escherichia coli genes but, strikingly, it also revealed putative alternative internal start sites in a number of genes. Experimental evidence demonstrated that the internal start codons can be recognized by the ribosomes and direct translation initiation in vitro and in vivo. Proteins, whose translation is initiated at an internal in-frame and out-of-frame start sites, can be functionally important and contribute to the ‘alternative’ bacterial proteome. In addition to proteome expansion, the internal start sites may play regulatory role in gene expression.
Project description:Cell size is tightly controlled in healthy tissues and single-celled organisms, but it remains unclear how cell size influences physiology. Increasing cell size was recently shown to remodel the proteomes of cultured human cells, demonstrating that large and small cells of the same type can be compositionally different. Here, we utilize the natural heterogeneity of hepatocyte ploidy and yeast genetics to establish that ploidy-to-cell size ratio is a highly conserved determinant of proteome composition. In both mammalian and yeast cells, genome dilution by cell growth elicits a starvation-like phenotype, suggesting that growth in large cells is restricted by genome concentration in manner that mimics a limiting nutrient. Moreover, genome dilution explains some proteomic changes ascribed to yeast aging. Overall, our data indicate that genome concentration drives changes in cell composition independently of external environmental cues.