# The Small Molecule SR8278 Inhibits Cell Proliferation Independent of the REV-ERB Nuclear Receptor Proteins in Human Keratinocytes

## TL;DR

The study shows that the small molecule SR8278 slows cell growth in human keratinocytes without acting through its originally identified target, the REV-ERB proteins.

## Contribution

The paper reveals that SR8278's anti-proliferative effects are independent of REV-ERB proteins, challenging prior assumptions about its mechanism.

## Key findings

- SR8278 impacts genes involved in the G1/S transition of the cell cycle in keratinocytes.
- The anti-proliferative effect of SR8278 is not mediated by REV-ERB proteins, as shown by CRISPR/Cas9 and siRNA experiments.
- SR8278 slows cell growth without causing genotoxic stress or apoptosis.

## Abstract

The small molecule SR8278 was initially identified as an antagonist of the REV-ERB (reverse c-ERBAa) nuclear receptor proteins, which play important roles in metabolism and circadian rhythms. Though SR8278 has been shown to have beneficial physiological effects in a variety of different preclinical disease contexts, its impact on gene expression and cell proliferation in keratinocytes has not previously been examined. We therefore carried out an RNA-seq analysis and found that genes involved in the G1/S transition of the cell cycle were significantly impacted by SR8278 treatment, and these effects were confirmed at both the RNA and protein level by RT-qPCR and Western blotting, respectively. Cell proliferation assays showed that SR8278 slowed cell growth but did not induce genotoxic stress or apoptosis. Finally, the use of CRISPR/Cas9 genome editing and siRNA-mediated disruption of REV-ERB gene expression showed that the loss of the REV-ERB proteins did not impact the effect of SR8278 on gene expression and cell proliferation. We conclude that the anti-proliferative effects of SR8278 are not mediated by the REV-ERB proteins, and, thus, care should be taken when interpreting studies involving this compound unless complementary genetic approaches are also shown, particularly in studies involving cell proliferation.