Abstract
A major challenge in biology is that genetically identical cells in the same environment can display gene expression stochasticity (noise), which contributes to bet-hedging, drug tolerance, and cell-fate switching. The magnitude and timescales of stochastic fluctuations can depend on the gene regulatory network. Currently, it is unclear how gene expression noise of specific networks impacts the evolution of drug resistance in mammalian cells. Answering this question requires adjusting network noise independently from mean expression. Here, we develop positive and negative feedback-based synthetic gene circuits to decouple noise from the mean for Puromycin resistance gene expression in Chinese Hamster Ovary cells. In low Puromycin concentrations, the high-noise, positive-feedback network delays long-term adaptation, whereas it facilitates adaptation under high Puromycin concentration. Accordingly, the low-noise, negative-feedback circuit can maintain resistance by acquiring mutations while the positive-feedback circuit remains mutation-free and regains drug sensitivity. These findings may have profound implications for chemotherapeutic inefficiency and cancer relapse.
Highlights
A major challenge in biology is that genetically identical cells in the same environment can display gene expression stochasticity, which contributes to bet-hedging, drug tolerance, and cell-fate switching
By comparing gene expression in Chinese Hamster Ovary (CHO) cell lines carrying each gene circuit, we establish decoupled noise points with different gene expression noise levels but with similar mean expression. By using these gene circuits to control the expression of the Puromycin N-acetyl-transferase (PuroR or pac) gene that confers resistance to the antibiotic Puromycin, we investigate how mNF and mammalian-optimized high-noise positivefeedback (mPF) gene expression noise influences mammalian drug resistance evolution
We find that the mPF gene circuit with high Puromycin resistance gene (PuroR) expression noise can aid longterm evolutionary adaptation of mammalian cells at the highest stress (Puromycin) level, whereas it has the opposite effect at low stress
Summary
A major challenge in biology is that genetically identical cells in the same environment can display gene expression stochasticity (noise), which contributes to bet-hedging, drug tolerance, and cell-fate switching. The magnitude and timescales of stochastic fluctuations can depend on the gene regulatory network It is unclear how gene expression noise of specific networks impacts the evolution of drug resistance in mammalian cells. The memory describes the time for which cells remain deviant once they depart from the average[11,12] These noise characteristics of a gene depend strongly on the regulatory network that embeds it. Hypotheses from over a decade ago propose that non-genetic heterogeneity aids cell survival during drug treatment[12,15,19,20] and other forms of environmental stress[21,22] These effects depend on the amplitude and memory of noise, both of which are network-dependent. Prior demonstration that noise can be harmful in low stress[19,22] cautions against the generality of these conclusions
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