Penn State researchers discovered that the CCR4-NOT protein complex acts as a genetic guardian in the nucleus, suppressing jumping genes and regulating transcription across the human genome to maintain cellular stability.
As much as half of the human genome consists of repetitive DNA sequences known as jumping genes, or transposable elements. These sequences can copy themselves and reinsert elsewhere in the genome, driving evolutionary diversity and helping regulate how other genes turn on or off. Yet their unchecked movement can destabilize genetic material, creating mutations linked to cancer, autoimmune diseases, and neurodevelopmental disorders. A team of scientists at Penn State University identified a defense mechanism that keeps these elements in check.
Uncovering the Nuclear Role of CCR4-NOT
Published in the Journal of Biological Chemistry, the study reveals a function for the CCR4-NOT protein complex within the cell nucleus. While scientists studied the complex in yeast and spent the past decade exploring its cytoplasmic duties in human cells—such as processing and degrading RNA—its exact role inside the nucleus remained largely unexplored until now.
In the past decade, its role in human cell lines has started to be explored, but those studies have focused mainly on characterizing its role in RNA processing and degradation. We wanted to learn more about its role in the nucleus of cells where it is involved in the production of RNA from a DNA template.
Shardul Kulkarni, assistant research professor of biochemistry and molecular biology in the Penn State Eberly College of Science
Testing Protein Knockdown Effects
To investigate nuclear activity, the research team utilized an auxin-induced degradation technique on a human cancer cell line provided by the U.S. National Institutes of Health. By genetically modifying two components of the CCR4-NOT complex, CNOT1 and CNOT4, the investigators engineered them to degrade within an hour of adding auxin. Although previous cytoplasmic experiments showed these two components had opposite effects, reducing their expression produced a unified and surprising response in the nucleus.
We were surprised that knock down of both CNOT1 and CNOT4 resulted in a rapid widespread increase of transcription across the genome.
Shardul Kulkarni, lead author
This surge in transcription included jumping genes, whose overall expression climbed sharply. Conversely, the expression levels of a specific family of protective genes dropped. These genes, known as the Kruppel-associated box-containing zinc nuclear finger (KZNF) family, serve as known repressors of transposable element activity.
Defending Against Genetic Instability
The findings point to a multi-layered regulatory network. The CCR4-NOT complex suppresses jumping genes primarily by regulating KZNF gene expression, preventing these potentially disruptive elements from being transcribed in the first place. The researchers also noted that the complex appears to control the stability of any RNA produced by transposable elements, adding an extra safeguard against unwanted genetic activity.
The research team included postdoctoral researcher Alexis Morrissey, data scientist Aswathy Sebastian, graduate student Oluwasegun T. Akinniyi, research professor of biochemistry and molecular biology Cheryl A. Keller, research professor of bioinformatics Istvan Albert, professor of biochemistry and molecular biology Shaun Mahony, and distinguished professor of biochemistry and molecular biology Joseph C. Reese. Financial support for the project was provided by the U.S. National Institutes of Health’s National Institute of General Medical Sciences under grants R35GM136353 and R35GM144135.