Abstract 4127: Oncogenic BRAF suppresses p53 function in melanoma through direct protein protein interaction

Oncogenic BRAF is a driver of approximately 8% of all cancers, with a particular prevalence in lung cancer, thyroid cancer, and cutaneous melanoma. BRAFV600E is the most common oncogenic alteration, accounting for about 50% of cutaneous melanoma cases. Combined inhibition of BRAFV600E plus MEK1/2 is the current targeted therapeutic option approved for the treatment of BRAFV600E-driven melanoma and lung cancer. Unfortunately, many patients only experience short-term therapeutic benefit with a mean progression-free survival of 7 to 14 months in non-small cell lung cancer and melanoma, respectively. Thus, this highlights the need to identify better therapeutic targets for BRAF-driven cancers. BRAFV600E is often referred to as a monomer as BRAFV600E signals independent of RAS-GTP and RAF dimerization. However, oncogeneic BRAF may still be dependent on other scaffolding proteins for optimal signaling. Thus, to evaluate this, we used gel filtration chromatography and immunoblotting analysis to visualize BRAF signaling complexes. These data revealed that BRAFV600E exists in a large multiprotein complex. Pharmacological inhibition of BRAFV600E shifted the elution of BRAFV600E complexes into lower molecular weight fractions. We further investigated this BRAFV600E signaling complex by implementing the proximity labeling technique, TurboID. Coupled with mass spectrometry, this technique enabled the unbiased identification of novel BRAF interactors and helped us understand how targeted therapy impacts this BRAF interactome. Here, we identified a multitude of unique wild-type BRAF and BRAFV600E interactors, with the tumor suppressor p53 being of particular interest. Intriguingly, TP53 alterations are infrequent in melanoma, prompting the hypothesis that by interacting with p53, BRAFV600E may influence p53 function. We show that BRAFV600E expression alters p53 subcellular localization, significantly reduces native p53 activity, and prevents p53 activation following UVB radiation and MDM2 inhibition. Ultimately, these findings provide unique mechanistic insight into the mechanisms by which BRAFV600E drives cancer development and may clarify why TP53 is infrequently altered in melanoma. Citation Format: Kayla T. O'Toole, Adamaris Martinez, Brandon Murphy, Deevya Baral, Anastasia Proveyeka, Fatima Al-Sudani, Joshua Andersen, Robert Judson-Torres, Martin McMahon. Oncogenic BRAF suppresses p53 function in melanoma through direct protein protein interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4127.