I wonder if cells slow down their protein expression and keep reusing the ones they have already made since they're not going through different phases and so the need to make/degrade proteins is lowered during G0 phase.
Any comments or paper referral will be much appreciated. Thanks!
G0 phase is certainly different when it comes to expression of the specific proteins implicated in the cell cycle regulation (such as cyclines) and DNA replication (e.g. helicases, topoisomerases, DNA-synthases etc.). However, when speaking of constitutive proteins, proteins that are normally expressed throughout the stationary phase of the cell's life, there is really no such thing as G0 specific pattern of global protein expression. Rather, one may say, that although overall protein synthesis rate in G0 phase is usually reduced relative to other interphase stages, the protein expression is always (under physiological conditions) the result of demands imposed on the individual cell. In other words, the cell adapts to the environmental changes (e.g. glucose depletion, heat shock, free radicals etc.) by modulating the expression of specific proteins. So, the summarized answer to your question will be: yes, during the G0 phase, cells downregulate some proteins that are upregulated in other stages of the interphase; cells in G0 phase slow down expression of some proteins, but the global protein synthesis rate will be primarily affected by the enviromental changes, and not directly by the cell cycle itself. Since every peptide has its half-life time, and thus the degradation rate, the demand of the protein renewal/synthesis will be constant under constant conditions, and will change as those conditions change, as a result of the cell's adaptation capacities.
Thank you Matija for your elaborate response. It was extremely helpful.
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