Cells fine-tune gene expression in response to cellular stress, a process critical for tumor progression that leads to cancer. However, elucidating mechanisms governing stress-responsive transcription remains an ongoing gap.
In a new study published in Nature Chemical Biology titled, “MED1 IDR deacetylation controls stress responsive genes through RNA Pol II recruitment,” researchers from Rockefeller University have identified a molecular switch in breast cancer cells that reprograms the genetic production line towards tumor growth and stress resistance.
“It’s another example of how basic research can open promising therapeutic avenues,” said Ran Lin, PhD, research associate at Rockefeller and first author of the study.
Robert Roeder, PhD, Arnold and Mabel Beckman Professor and co-corresponding author of the study emphasizes that this molecular switch is mediated by a generic transcription complex normally required for all protein-coding genes. “But what was most unexpected is that its individual subunits can be repurposed for several physiological functions—including a function that allows cancer cells to survive and grow in high-stress environments,” he said.
To initiate transcription, RNA polymerase II (Pol II) functions with the Mediator complex, a large transcriptional coactivator protein composed of 30 subunits. MED1 is a key subunit of the complex essential for Pol II transcription in different types of cells, including estrogen receptor–positive breast cancer (ER+ BC), one of the most common forms of the disease.
Previous research on ER+ BC has shown that estrogen receptor interactions with MED1 drive gene activation and render otherwise promising cancer drugs ineffective. Given this, the authors explored whether MED1 post-translational modifications played a role in this mechanism. Notably, acetylation has been increasingly recognized for its influential role in tumor development, metastasis, and drug resistance.
After confirming MED1 acetylation, the authors aimed to understand how this modification influences protein function, especially under cellular stress. Cells were subjected to different types of stress conditions, including hypoxia (lack of oxygen), oxidative stress, and thermal stress and found that the protein, SIRT1, removes acetyl groups from normal MED1. This deacetylation enables MED1 to interact more efficiently with Pol II, leading to the elevated potential for activation of protective genes.
When MED1 mutants with removed, the acetylation sites were introduced into ER+ breast cancer cells, results showed that the breast cancer cells with deacetylated MED1 formed faster-growing and more stress-resistant tumors. The work emphasizes that acetylation and deacetylation of MED1 acts as a regulatory switch that helps cancer cells reprogram transcription in response to stress, supporting both survival and growth.
“In cancer—particularly in ER+ breast cancer—this pathway may be co-opted or intensified to support abnormal growth and survival. We hope these insights will inform future drug development, especially for breast cancers and possibly other malignancies that rely on stress-induced gene reprogramming,” said Lin.
“This MED1 regulatory pathway appears to be part of a wider paradigm in which acetylation regulates transcription factors,” Roeder adds. “Our earlier work on p53 helped establish that principle. Continuing to probe these basic mechanisms is what allows us to identify pathways that may eventually be leveraged for therapeutic purposes.”
