Eye Cancer’s Hidden Weakness: CRISPR Screens Expose p300 as a Lifeline for GNAQ-Mutant Tumors

Uveal melanoma, the most common primary cancer of the eye in adults, has long frustrated oncologists. Unlike its cutaneous cousin, it is rarely driven by mutations in BRAF or other well-known oncogenes; instead, the vast majority of these tumors carry activating mutations in GNAQ or GNA11, two genes encoding the G proteins Gαq and Gα11. Yet decades of effort to drug these mutated G proteins directly have yielded little, and once the disease spreads to the liver, treatment options remain painfully limited. A new study published in Nature Communications now offers a fresh angle of attack, identifying an unexpected molecular dependency that these tumors cannot survive without.

The research, led by Gui-Ming Zhang, Le Yu and colleagues at Southern Medical University and collaborating institutions in China, took a deliberately indirect route. Rather than trying to block the oncogenic signal at its source, the team asked a different question: which genes does a cancer cell become fatally dependent on once GNAQ has been mutated? This concept, known as synthetic lethality, exploits the idea that a mutation that is harmless on its own can become lethal when a second, compensating function is removed. In practice, it means that a drug targeting the partner vulnerability can kill cancer cells while sparing normal tissue, which lacks the initiating mutation.

To find such vulnerabilities systematically, the researchers used an isogenic CRISPR screening approach. They engineered pairs of cell lines that were genetically identical except for the presence or absence of oncogenic GNAQ signaling, and then used CRISPR-based gene knockout across the genome to see which losses were selectively catastrophic only in the mutant cells. This design filters out genes that are generally essential for all cells and isolates those whose importance is specifically created by the cancer-driving mutation. Among the top-ranked hits, one gene stood out: EP300, which encodes p300, a protein lysine acetyltransferase that decorates histones and other proteins with acetyl groups to regulate gene expression.

Notably, the screen also flagged CREBBP, the gene encoding CBP, a closely related paralogue of p300 that shares much of its catalytic machinery and often partners with it at regulatory DNA. The convergence of both paralogues near the top of the candidate list suggested that the dependency was not a screening artifact but a genuine, redundant axis that GNAQ-mutant cells rely upon. Because p300 and CBP sit at the interface between signaling pathways and the epigenetic machinery that executes gene expression programs, their identification pointed the investigators toward a specific mechanism worth dissecting in detail.

That mechanism turned out to involve YAP, the transcriptional co-activator that serves as the main effector of the Hippo signaling pathway. When the Hippo pathway is switched off, YAP accumulates in the nucleus and teams up with DNA-binding transcription factors to activate genes promoting cell growth, survival and migration. Oncogenic Gαq is known to feed into this pathway, driving unrestrained YAP activity in uveal melanoma. The new work shows that p300 and CBP are not passive bystanders in this process: they physically interact with YAP at chromatin, the packaged form of DNA inside the nucleus, and this interaction is what allows the YAP program to be fully executed.

At the chromatin level, the researchers found that p300 and CBP enhance the acetylation of histone H3 at lysine 27, a chemical mark abbreviated H3K27ac that flags active promoters and putative enhancers, the regulatory regions that boost gene transcription. In GNAQ-mutant cells, this acetylation is concentrated at the regulatory elements of YAP target genes. The histone mark, in turn, promotes the recruitment of RNA polymerase II, the enzyme that reads genes into messenger RNA, together with CDK9, a kinase that helps release the paused polymerase into productive elongation. In other words, p300 and CBP act as the chromatin-level engine that converts YAP’s presence at DNA into actual gene output, and without them the oncogenic transcriptional program stalls.

The functional consequences of this dependency were tested rigorously in animal models. The team employed multiple in vivo models representing clinically relevant stages of Gαq-mutant uveal melanoma, from primary tumor growth to metastatic spread, the stage that matters most for patient survival. Both genetic approaches, which remove p300 function directly, and pharmacological inhibitors of its acetyltransferase activity profoundly impaired tumor growth and metastasis in these models. The consistency between genetic and drug-based suppression strengthens the case that the effect is genuinely mediated by p300’s enzymatic function rather than some scaffolding role or off-target toxicity, and it provides a direct preclinical rationale for moving toward therapeutic inhibition.

The significance of the finding lies in its strategic positioning. Because the dependency is created by the oncogenic Gαq pathway itself, p300 inhibition represents a form of indirect targeting: the drug does not need to shut down the mutated G protein, which has proved chemically difficult, but instead blocks an essential downstream enabler of the cancer’s transcriptional addiction. Epigenetic enzymes such as p300 and CBP are increasingly considered druggable, and small-molecule acetyltransferase inhibitors are an active area of medicinal chemistry. The study thereby converts a hard-to-drug oncogene problem into a potentially tractable epigenetic one, a reframing that could reshape how the field approaches GNAQ- and GNA11-driven cancers more broadly.

There are, of course, caveats that temper immediate clinical translation. p300 and CBP perform essential functions in many normal cell types, including roles in hematopoiesis and general transcriptional regulation, so therapeutic windows will need to be carefully defined, and the authors note that their work establishes p300 as a potential therapeutic target rather than a validated drug. The pharmacological results come from preclinical models, and the behavior of human metastatic disease in patients may introduce additional dependencies and resistances not captured in the laboratory. Nonetheless, the synthetic lethal logic demonstrated here, in which the very mutation that drives the cancer also creates its Achilles’ heel, is exactly the kind of therapeutic principle that has succeeded in other hard-to-treat tumors, such as PARP inhibition in BRCA-mutant breast and ovarian cancers.

For patients with metastatic uveal melanoma, whose median survival has remained dismal for decades, the study offers something the field has lacked: a mechanistically grounded, experimentally validated vulnerability that is specific to the molecular engine of their disease. By showing that GNAQ-mutant tumors depend on the p300/CBP chromatin machinery to sustain YAP-driven transcription, the researchers have charted a path from genome-wide screening to a defined mechanism to in vivo efficacy. The next steps, developing or deploying clinically suitable acetyltransferase inhibitors and testing them in appropriately designed trials, will determine whether this laboratory insight can be converted into a real therapeutic option for one of oncology’s most neglected cancers.

Subject of Research: Synthetic lethal identification of p300/CBP as a therapeutic vulnerability in GNAQ-mutant uveal melanoma

Article Title: Synthetic lethal screens reveal p300/CBP as a vulnerability for GNAQ-driven uveal melanomas

Article References: Zhang, G.-M., Yuan, J., Chen, L., Jin, X.-Y., Ren, Z.-L., Zhou, Y.-L., Zhou, R., Xiao, Y.-F., Wang, J.-W., Zhang, X.-A., Bai, C., Li, Z., Li, Y.-L., & Yu, L. (2026). Synthetic lethal screens reveal p300/CBP as a vulnerability for GNAQ-driven uveal melanomas. Nature Communications. https://doi.org/10.1038/s41467-026-77999-8

Image Credits: AI Generated

DOI: 10.1038/s41467-026-77999-8

Keywords: uveal melanoma, GNAQ, p300, CBP, YAP, synthetic lethality, CRISPR screen, epigenetics, H3K27 acetylation, Hippo pathway, targeted therapy, eye cancer