Mitochondrial Enzyme SUCLG2 Emerges as a Tumor Suppressor in Colorectal Cancer

A mitochondrial enzyme long known simply as a workhorse of cellular energy production has been revealed as a powerful suppressor of colorectal cancer, one of the most common and deadly malignancies worldwide. In a study published in Cancer Cell International, researchers report that SUCLG2, the beta subunit of the GDP-forming succinyl-CoA ligase, is markedly depleted in colorectal tumors and that its loss permits malignant cells to proliferate, invade, and progress to advanced disease. The work, led by Tao Guo, Suhe Lai, Minli Yang, and Jinjun Guo of Bishan Hospital of Chongqing Medical University and collaborators, demonstrates that restoring SUCLG2 reawakens a dormant anti-cancer circuit centered on the p53 tumor suppressor pathway, offering a fresh conceptual link between metabolism and epigenetic control of gene expression in cancer.

The investigation began with an integrated bioinformatics screen of colorectal cancer datasets, from which SUCLG2 emerged as a candidate gene whose expression tracks with disease severity. Multi-omics validation in clinical specimens confirmed the pattern: SUCLG2 levels were significantly downregulated in colorectal cancer tissue compared with healthy tissue, and the degree of loss correlated tightly with advanced TNM staging and poor patient prognosis. Patients whose tumors expressed the least SUCLG2 fared worst, positioning the enzyme not only as a mechanistic player but also as a potential prognostic biomarker that could help clinicians stratify risk at the time of diagnosis.

To probe function, the team manipulated SUCLG2 in colorectal cancer cell lines and in animal models. Functional assays showed that SUCLG2 restrains the proliferation of colorectal cancer cells in culture and suppresses xenograft tumor growth in vivo. When the enzyme was depleted, cells grew more aggressively; when it was restored, growth slowed appreciably. These results established SUCLG2 as a bona fide tumor suppressor rather than a metabolic bystander, raising the central question of how a tricarboxylic acid cycle enzyme exerts such direct control over cancer cell behavior.

The answer, uncovered through transcriptomic, metabolomic, and epigenetic analyses, lies in an unexpected biochemical pathway involving S-adenosylmethionine, or SAM, the universal methyl donor of the cell. SUCLG2 activity reduces intracellular SAM levels. Because SAM is the substrate required by DNA methyltransferases, or DNMTs, to attach methyl groups to DNA, lower SAM availability dampens DNMT activity genome-wide. The consequence for colorectal cancer cells is profound: hypermethylation of tumor suppressor gene promoters is alleviated, and genes silenced by this epigenetic brake can be switched back on.

Among the genes reactivated by this mechanism, one stood out. GADD45G, a growth arrest and DNA damage-inducible gene with well-documented anti-proliferative functions, regained transcriptional activity when SUCLG2 was present. The researchers showed that SUCLG2 demethylates the GADD45G promoter through this SAM-dependent epigenetic remodeling, relieving promoter hypermethylation and restoring GADD45G expression. Gene set enrichment analysis reinforced the picture, revealing that SUCLG2 overexpression activates p53 and apoptosis signaling while inhibiting cell cycle pathways, consistent with GADD45G acting as a conduit between the mitochondrial enzyme and the cell’s central tumor-suppressive machinery.

Causality was tested directly. When the researchers knocked down GADD45G in cells engineered to overexpress SUCLG2, the tumor-suppressive effects of the enzyme were largely abolished. This loss-of-function experiment established GADD45G as a critical downstream mediator of the SUCLG2/p53 signaling axis. In other words, SUCLG2 does not simply slow cancer cells through metabolic exhaustion; it reactivates a specific genetic program, via demethylation of GADD45G, that engages p53-mediated growth inhibition and programmed cell death.

Clinical validation strengthened the mechanistic model considerably. Across patient cohorts, the team confirmed a robust positive correlation between SUCLG2 and GADD45G expression, and, in keeping with the proposed epigenetic mechanism, a negative correlation between SUCLG2 levels and methylation of the GADD45G promoter. Tumors with abundant SUCLG2 tended to carry unmethylated, transcriptionally active GADD45G, whereas SUCLG2-poor tumors showed the silenced, hypermethylated state. These correlative findings in human tissue mirror the experimental results and suggest that the SAM-DNMT-GADD45G axis operates in actual disease, not merely in laboratory models.

The study carries notable therapeutic implications. Epigenetic silencing of tumor suppressor genes is a hallmark of colorectal cancer, and demethylating agents exist but act globally, with limited specificity and considerable toxicity. If SUCLG2 activity, or downstream nodes of its pathway, could be pharmacologically enhanced, it might offer a more targeted way to lift methylation repression specifically at tumor suppressor promoters. Alternatively, the SUCLG2-GADD45G-p53 axis could be exploited indirectly, for example by screening for compounds that mimic the enzyme’s effect on SAM metabolism or DNMT activity. The authors position SUCLG2 as both a promising prognostic biomarker and a candidate therapeutic target, though translating these findings into clinical interventions will require further preclinical development and validation in larger patient populations.

Beyond its immediate clinical relevance, the research adds to a growing appreciation that metabolic enzymes can double as epigenetic regulators. Because metabolites such as SAM, alpha-ketoglutarate, acetyl-CoA, and NAD+ serve as substrates and cofactors for chromatin-modifying enzymes, shifts in cellular metabolism can directly reshape the epigenetic landscape. The SUCLG2 story is a vivid example: a change in the activity of a TCA cycle enzyme propagates through the methyl donor economy of the cell to determine whether a key anti-cancer gene is audible or silenced. As colorectal cancer remains a major clinical challenge, uncovering such regulatory mechanisms may open entirely new avenues for early detection, risk stratification, and treatment.

Subject of Research: SUCLG2-mediated epigenetic activation of the GADD45G-p53 axis in colorectal cancer progression

Article Title: SUCLG2 demethylates GADD45G to activate the p53 pathway and inhibit malignant progression in colorectal cancer

Article References: Guo, T., Lai, S., Yang, K., Tong, J., Liao, G., Lu, L., Jiang, C., Liu, H., Wu, Z., Yang, M., & Guo, J. (2026). SUCLG2 demethylates GADD45G to activate the p53 pathway and inhibit malignant progression in colorectal cancer. Cancer Cell International. https://doi.org/10.1186/s12935-026-04454-5

Image Credits: AI Generated

DOI: 10.1186/s12935-026-04454-5

Keywords: colorectal cancer, SUCLG2, GADD45G, p53 pathway, DNA methylation, demethylation, S-adenosylmethionine, DNA methyltransferase, tumor suppressor, cancer metabolism, epigenetics, prognostic biomarker