Purpose: Uveal melanoma is the most common eye cancer in adults. Approximately 50% of patients with uveal melanoma develop metastatic uveal melanoma (mUM) in the liver, even after successful treatment of the primary lesions. mUM is refractory to current chemo- and immune-therapies, and most mUM patients die within a year. Uveal melanoma is characterized by gain-of-function mutations in GNAQ/GNA11, encoding Gαq proteins. We have recently shown that the Gαq–oncogenic signaling circuitry involves a noncanonical pathway distinct from the classical activation of PLCβ and MEK–ERK. GNAQ promotes the activation of YAP1, a key oncogenic driver, through focal adhesion kinase (FAK), thereby identifying FAK as a druggable signaling hub downstream from GNAQ. However, targeted therapies often activate compensatory resistance mechanisms leading to cancer relapse and treatment failure.Experimental Design: We performed a kinome-wide CRISPR-Cas9 sgRNA screen to identify synthetic lethal gene interactions that can be exploited therapeutically. Candidate adaptive resistance mechanisms were investigated by cotargeting strategies in uveal melanoma and mUM in vitro and in vivo experimental systems.Results: sgRNAs targeting the PKC and MEK–ERK signaling pathways were significantly depleted after FAK inhibition, with ERK activation representing a predominant resistance mechanism. Pharmacologic inhibition of MEK and FAK showed remarkable synergistic growth-inhibitory effects in uveal melanoma cells and exerted cytotoxic effects, leading to tumor collapse in uveal melanoma xenograft and liver mUM models in vivo.Conclusions: Coupling the unique genetic landscape of uveal melanoma with the power of unbiased genetic screens, our studies reveal that FAK and MEK–ERK cotargeting may provide a new network-based precision therapeutic strategy for mUM treatment.See related commentary by Harbour, p. 2967

Obesity, defined as a body mass index (BMI) ≥ 30, is an established risk factor for breast cancer among women in the general population after menopause. Whether elevated BMI is a risk factor for women with a germline mutation in BRCA1 or BRCA2 is less clear because of inconsistent findings from epidemiological studies and a lack of mechanistic studies in this population. Here, we show that DNA damage in normal breast epithelia of women carrying a BRCA mutation is positively correlated with BMI and with biomarkers of metabolic dysfunction. In addition, RNA sequencing showed obesity-associated alterations to the breast adipose microenvironment of BRCA mutation carriers, including activation of estrogen biosynthesis, which affected neighboring breast epithelial cells. In breast tissue explants cultured from women carrying a BRCA mutation, we found that blockade of estrogen biosynthesis or estrogen receptor activity decreased DNA damage. Additional obesity-associated factors, including leptin and insulin, increased DNA damage in human BRCA heterozygous epithelial cells, and inhibiting the signaling of these factors with a leptin-neutralizing antibody or PI3K inhibitor, respectively, decreased DNA damage. Furthermore, we show that increased adiposity was associated with mammary gland DNA damage and increased penetrance of mammary tumors in Brca1 ^+/− mice. Overall, our results provide mechanistic evidence in support of a link between elevated BMI and breast cancer development in BRCA mutation carriers. This suggests that maintaining a lower body weight or pharmacologically targeting estrogen or metabolic dysfunction may reduce the risk of breast cancer in this population.

β-arrestins play a key role in G protein-coupled receptor (GPCR) internalization, trafficking, and signaling. Whether β-arrestins act independently of G protein-mediated signaling has not been fully elucidated. Studies using genome-editing approaches revealed that whereas G proteins are essential for mitogen-activated protein kinase activation by GPCRs., β-arrestins play a more prominent role in signal compartmentalization. However, in the absence of G proteins, GPCRs may not activate β-arrestins, thereby limiting the ability to distinguish G protein from β-arrestin-mediated signaling events. We used β2-adrenergic receptor (β2AR) and its β2AR-C tail mutant expressed in human embryonic kidney 293 cells wildtype or CRISPR-Cas9 gene edited for Gα_s, β-arrestin1/2, or GPCR kinases 2/3/5/6 in combination with arrestin conformational sensors to elucidate the interplay between Gα_s and β-arrestins in controlling gene expression. We found that Gα_s is not required for β2AR and β-arrestin conformational changes, β-arrestin recruitment, and receptor internalization, but that Gα_s dictates the GPCR kinase isoforms involved in β-arrestin recruitment. By RNA-Seq analysis, we found that protein kinase A and mitogen-activated protein kinase gene signatures were activated by stimulation of β2AR in wildtype and β-arrestin1/2-KO cells but absent in Gα_s-KO cells. These results were validated by re-expressing Gα_s in the corresponding KO cells and silencing β-arrestins in wildtype cells. These findings were extended to cellular systems expressing endogenous levels of β2AR. Overall, our results support that Gs is essential for β2AR-promoted protein kinase A and mitogen-activated protein kinase gene expression signatures, whereas β-arrestins initiate signaling events modulating Gα_s-driven nuclear transcriptional activity.

Background/Objectives: Uveal melanoma (UVM), the leading primary intraocular cancer in adults, is driven by GNAQ/GNA11 mutations, encoding the active forms of Gαq proteins. While local treatments like surgery or radiation can control primary tumors, nearly half of patients die from metastasis. Our aim was identifying potential pathways involved in resistance to targeted therapy in UVM. Methods: Here, we screened 100 pathway-activating mutant complementary DNAs by lentiviral overexpression to identify those that enhance the survival of cancer cells in the presence of clinically relevant targeted therapies, using BAP1 wild-type UVM cells and validated the most significant results in BAP1-mutant cells. Results: This revealed JAK/STAT activation, overexpression of anti-apoptotic BCL2/BCL-XL, and dysregulated PI3K/mTOR or Hippo pathways as escape routes under MEK-ERK or FAK inhibition. Bioinformatic analysis of UVM transcriptome in TCGA further showed that high expression of the hallmark PI3K/AKT/mTOR pathway and IL6/JAK/STAT signaling correlates with poor prognosis. A similar correlation was shown by YAP and anti-apoptotic signatures. The analysis of individual representative genes from these signatures revealed that MTOR, BCL2L1 (BCL-XL), and TEAD4 gene expression are linked to poorer survival, underscoring the potential clinical impact of these adaptive pathways. Proliferation and apoptosis assay demonstrated that aberrant activation of AKT and YAP promotes resistance to FAK and MEK inhibitors. Conclusions: These findings support the adaptability of UVM lesions and suggest rational combination therapies targeting both primary GNAQ/GNA11-driven oncogenic signals and their compensatory networks as a more effective, personalized treatment approach for advanced UVM.

Supplementary figure 3. MEKi/FAKi combination reduces UM cells growth in xenograft tumor models with limited toxicity.