This study:

  • Demonstrated that cocaine increases expression of the protein E2F3a in the brain's reward system.
  • Suggests that E2F3a elevation functions as a master switch for changes in gene
  • expression that give rise to cocaine-related behaviors.

NIDA-supported researchers have shown that increased levels of a single protein in the brain's reward center are indispensable for producing some of cocaine's addiction-like effects in animals. Their findings highlight the involvement of a specific set of genes in the production of behavioral responses to cocaine and could point the way to medications to reduce the drug's hold on people.

See text descriptionFigure 1. Cocaine Exposure Increases E2F3a in the NAc To compensate for experimental variation in the isolation and measurement of E2F3a, the researchers also measured the levels of the protein actin, which is present in constant levels in all cells, and then determined the E2F3a/actin ratio. This ratio was arbitrarily set to 1.0 in saline-treated mice (blue bars). Compared with these animals, those administered cocaine (red bars) had higher levels of E2F3a. The increase in E2F3a was greater in the nucleus than in the surrounding cellular fluid (cytosol), consistent with E2F3a's known actions on DNA. *Statistically significant difference (p <0.05).
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Dr. Hannah Cates, Dr. Eric Nestler, and colleagues from the Icahn School of Medicine at Mount Sinai in New York City demonstrated that cocaine increases expression of the gene (E2f3a) that produces the protein E2F3a in the mouse nucleus accumbens (NAc). The researchers repeatedly exposed mice to the drug, then used immunohistochemistry to compare NAc E2F3a levels in these animals and a control group of unexposed mice. The protein was markedly more abundant in the exposed animals (see Figure 1).

Dr. Cates and Dr. Nestler and colleagues next showed that increased E2F3a levels are a necessary and sufficient condition for two important addiction-like behavioral responses to cocaine. In these experiments, the researchers either enhanced or blocked expression of the E2f3a gene selectively in the NAc of mice and then assessed the animals' behavior after cocaine exposure. Mice with enhanced E2f3a expression—and thereby increased levels of the protein—exhibited locomotor stimulation and place preference responses after fewer repeated doses of cocaine compared with normal mice. Conversely, mice in which the E2f3a gene was suppressed required more repeated doses of the drug to develop the responses, compared with normal mice.

The E2F3a protein is a transcription factor; it attaches to the DNA of target genes and increases or decreases the genes' expression. The Mount Sinai researchers propose that when repeated cocaine exposure increases E2F3a, it disrupts the protein's regulation of its target genes, resulting in changes to cell structure and function that give rise to behavioral responses (see Figure 2). Consistent with this proposal, the researchers showed that increasing E2F3a in the absence of cocaine reproduced a large fraction of the same alterations in gene expression that repeated cocaine exposure produces, and which other research has associated with behavioral responses to the drug (see Figure 3).

See text descriptionFigure 2. Cocaine-Induced Increases in E2F3a Change Expression of E2F3a's Target Genes and May Underlie Behavioral Responses to the Drug E2F3a enhances transcription of some of its target genes and inhibits transcription of others, and increased production of E2F3a amplifies these effects. Changes in cell structure and function may result that in turn give rise to behavioral responses such as enhanced locomotor activity or increased place preference.
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See text descriptionFigure 3. In the NAc, E2F3a Alters Expression of Many of the Same Genes As Cocaine The researchers compared the expression of all genes in the NAc of a) untreated animals, b) animals treated with cocaine, and c) animals treated to overproduce E2F3a. They identified genes whose expression was enhanced after both treatments (lower left quadrant), those whose expression was reduced after both treatments (upper right quadrant), and those whose expression was enhanced after one treatment but reduced after the other treatment (upper left and lower right quadrants). The odds were greatest that E2F3a overproduction increased expression of the same genes as did cocaine (gray quadrant) and, to a lesser extent, that E2F3a overproduction decreased expression of the same genes as did cocaine (blue quadrant).
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Dr. Nestler concludes, "This study provided robust evidence that E2F3a is centrally involved in mediating the effects of repeated cocaine exposure on both behavior and gene expression in the brain's reward pathway." In follow-up research, he continues, "We are now defining the range of target genes through which E2F3a produces its behavioral and molecular actions. In the longer term, we hope to use this information to expand the range of targets against which novel therapeutics for cocaine addiction could be developed."

This study was supported by NIH grants DA007359 and DA008227.


Cates, H.M., Heller, E.A., Lardner, C.K., et al. Transcription factor E2F3a in nucleus accumbens affects cocaine action via transcription and alternative splicing. Biol Psychiatry 84(3):167–179, 2018.