A key role for mitochondrial gatekeeper pyruvate dehydrogenase in oncogene-induced senescence

In response to tenacious stress signals, such as the unscheduled activation of oncogenes, cells can mobilize tumour suppressor networks to avert the hazard of malignant transformation. A large body of evidence indicates that oncogene-induced senescence (OIS) acts as such a break, withdrawing cells from the proliferative pool almost irreversibly, thus crafting a vital pathophysiological mechanism that protects against cancer. Despite the widespread contribution of OIS to the cessation of tumorigenic expansion in animal models and humans, we have only just begun to define the underlying mechanism and identify key players. Although deregulation of metabolism is intimately linked to the proliferative capacity of cells and senescent cells are thought to remain metabolically active, little has been investigated in detail about the role of cellular metabolism in OIS. Here we show, by metabolic profiling and functional perturbations, that the mitochondrial gatekeeper pyruvate dehydrogenase (PDH) is a crucial mediator of senescence induced by BRAFV600E, an oncogene commonly mutated in melanoma and other cancers. BRAFV600E-induced senescence was accompanied by simultaneous suppression of the PDH-inhibitory enzyme pyruvate dehydrogenase kinase 1 (PDK1) and induction of the PDH-activating enzyme pyruvate dehydrogenase phosphatase 2 (PDP2). The resulting combined activation of PDH enhanced the use of pyruvate in the tricarboxylic acid cycle, causing increased respiration and redox stress. Abrogation of OIS, a rate-limiting step towards oncogenic transformation, coincided with reversion of these processes. Further supporting a crucial role of PDH in OIS, enforced normalization of either PDK1 or PDP2 expression levels inhibited PDH and abrogated OIS, thereby licensing BRAFV600E-driven melanoma development. Finally, depletion of PDK1 eradicated melanoma subpopulations resistant to targeted BRAF inhibition, and caused regression of established melanomas. These results reveal a mechanistic relationship between OIS and a key metabolic signalling axis, which may be exploited therapeutically

Exit from quiescence displays a memory of cell growth and division

Reactivating quiescent cells to proliferate is critical to tissue repair and homoeostasis. Quiescence exit is highly noisy even for genetically identical cells under the same environmental conditions. Deregulation of quiescence exit is associated with many diseases, but cellular mechanisms underlying the noisy process of exiting quiescence are poorly understood. Here we show that the heterogeneity of quiescence exit reflects a memory of preceding cell growth at quiescence induction and immediate division history before quiescence entry, and that such a memory is reflected in cell size at a coarse scale. The deterministic memory effects of preceding cell cycle, coupled with the stochastic dynamics of an Rb-E2F bistable switch, jointly and quantitatively explain quiescence-exit heterogeneity. As such, quiescence can be defined as a distinct state outside of the cell cycle while displaying a sequential cell order reflecting preceding cell growth and division variations.NSF [DMS1463137, DMS1418172]; NSF of China and Anhui Province [31500676, 1508085SQC202]; NIH [CA09213, GM084905]; DARPA [WF911NF-14-1-0395]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

A Conserved Cell Growth Cycle Can Account for the Environmental Stress Responses of Divergent Eukaryotes

The respiratory metabolic cycle in budding yeast (Saccharomyces cerevisiae) consists of two phases most simply defined phenomenologically: low oxygen consumption (LOC) and high oxygen consumption (HOC). Each phase is associated with the periodic expression of thousands of genes, producing oscillating patterns of gene-expression found in synchronized cultures and in single cells of slowly growing unsynchronized cultures. Systematic variation in the durations of the HOC and LOC phases can account quantitatively for well-studied transcriptional responses to growth rate differences. Here we show that a similar mechanism, transitions from the HOC phase to the LOC phase, can account for much of the common environmental stress response (ESR) and for the cross protection by a preliminary heat stress (or slow growth rate) to subsequent lethal heat-stress. Similar to the budding yeast metabolic cycle, we suggest that a metabolic cycle, coupled in a similar way to the ESR, in the distantly related fission yeast, Schizosaccharomyces pombe, and in human can explain gene-expression and respiratory patterns observed in these organisms. Although metabolic cycling is associated with the G0/G1 phase of the cell division cycle of slowly growing budding yeast, transcriptional cycling was detected in the G2 phase of the division cycle in fission yeast, consistent with the idea that respiratory metabolic cycling occurs during the phases of the cell division cycle associated with mass accumulation in these divergent eukaryotes.National Institutes of Health (U.S.) (GM046406)National Institutes of Health (U.S.). Pioneer Award (1DP1OD003936)National Science Foundation (U.S.) (ECCS 0835623)National Institutes of Health (U.S.) (GM096193)National Institutes of Health (U.S.)National Institutes of Health (U.S.) (U54CA143874)National Institute of General Medical Sciences (U.S.). Center for Quantitative Biology (GM071508

The proteomics of quiescent and nonquiescent cell differentiation in yeast stationary-phase cultures

Starved yeast cultures differentiate into quiescent (Q) and nonquiescent (NQ) cell fractions. The yeast GFP-fusion library (4159 strains) and high-throughput flow cytometry were used to study this process. This showed significant metabolic and physiologic differences between Q/NQ cells and provided new tools for studying their differentiation