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Inactivating mutations in PTEN are prevalent in melanoma and are thought to support tumor development by hyperactivating the AKT/mTOR pathway. Conversely, activating mutations in AKT are relatively rare in melanoma, and therapies targeting AKT or mTOR have shown disappointing outcomes in preclinical models and clinical trials of melanoma. This has led to the speculation that PTEN suppresses melanoma by opposing AKT-independent pathways, potentially through noncanonical functions beyond its lipid phosphatase activity. In this study, we examined the mechanisms of PTEN-mediated suppression of melanoma formation through the restoration of various PTEN functions in PTEN-deficient cells or mouse models. PTEN lipid phosphatase activity predominantly inhibited melanoma cell proliferation, invasion, and tumor growth, with minimal contribution from its protein phosphatase and scaffold functions. A drug screen underscored the exquisite dependence of PTEN-deficient melanoma cells on the AKT/mTOR pathway. Furthermore, activation of AKT alone was sufficient to counteract several aspects of PTEN-mediated melanoma suppression, particularly invasion and the growth of allograft tumors. Phosphoproteomics analysis of the lipid phosphatase activity of PTEN validated its potent inhibition of AKT and many of its known targets, while also identifying the AP-1 transcription factor FRA1 as a downstream effector. The restoration of PTEN dampened FRA1 translation by inhibiting AKT/mTOR signaling, and FRA1 overexpression negated aspects of PTEN-mediated melanoma suppression akin to AKT. This study supports AKT as the key mediator of PTEN inactivation in melanoma and identifies an AKT/mTOR/FRA1 axis as a driver of melanomagenesis., Significance: PTEN suppresses melanoma predominantly through its lipid phosphatase function, which when lost, elevates FRA1 levels through AKT/mTOR signaling to promote several aspects of melanomagenesis., (©2024 American Association for Cancer Research.)

Activating mutations in BRAF, a key mediator of RAS signaling, are present in approximately 50% of melanoma patients. Pharmacologic inhibition of BRAF or the downstream MAP kinase MEK is highly effective in treating BRAF-mutant melanoma. In contrast, RAS pathway inhibitors have been less effective in treating epithelial malignancies, such as lung cancer. Here, we show that treatment of melanoma patients with BRAF and MEK inhibitors (MEKi) activated tumor NF-κB activity. MEKi potentiated the response to TNFα, a potent activator of NF-κB. In both melanoma and lung cancer cells, MEKi increased cell-surface expression of TNFα receptor 1 (TNFR1), which enhanced NF-κB activation and augmented expression of genes regulated by TNFα and IFNγ. Screening of 289 targeted agents for the ability to increase TNFα and IFNγ target gene expression demonstrated that this was a general activity of inhibitors of MEK and ERK kinases. Treatment with MEKi led to acquisition of a novel vulnerability to TNFα and IFNγ-induced apoptosis in lung cancer cells that were refractory to MEKi killing and augmented cell-cycle arrest. Abolishing the expression of TNFR1 on lung cancer cells impaired the antitumor efficacy of MEKi, whereas the administration of TNFα and IFNγ in MEKi-treated mice enhanced the antitumor response. Furthermore, immunotherapeutics known to induce expression of these cytokines synergized with MEKi in eradicating tumors. These findings define a novel cytokine response modulatory function of MEKi that can be therapeutically exploited. SIGNIFICANCE: Lung cancer cells are rendered sensitive to MEK inhibitors by TNFα and IFNγ, providing a strong mechanistic rationale for combining immunotherapeutics, such as checkpoint blockers, with MEK inhibitor therapy for lung cancer. See related commentary by Havel, p. 5699 ., (©2019 American Association for Cancer Research.)

Oncogenic kinase fusions of ALK , ROS1 , RET , and NTRK1 act as drivers in human lung and other cancers. Residual tumor burden following treatment of ALK or ROS1 + lung cancer patients with oncogene-targeted therapy ultimately enables the emergence of drug-resistant clones, limiting the long-term effectiveness of these therapies. To determine the signaling mechanisms underlying incomplete tumor cell killing in oncogene-addicted cancer cells, we investigated the role of EGFR signaling in drug-naïve cancer cells harboring these oncogene fusions. We defined three distinct roles for EGFR in the response to oncogene-specific therapies. First, EGF-mediated activation of EGFR blunted fusion kinase inhibitor binding and restored fusion kinase signaling complexes. Second, fusion kinase inhibition shifted adaptor protein binding from the fusion oncoprotein to EGFR. Third, EGFR enabled bypass signaling to critical downstream pathways such as MAPK. While evidence of EGFR-mediated bypass signaling has been reported after ALK and ROS1 blockade, our results extended this effect to RET and NTRK1 blockade and uncovered the other additional mechanisms in gene fusion-positive lung cancer cells, mouse models, and human clinical specimens before the onset of acquired drug resistance. Collectively, our findings show how EGFR signaling can provide a critical adaptive survival mechanism that allows cancer cells to evade oncogene-specific inhibitors, providing a rationale to cotarget EGFR to reduce the risks of developing drug resistance. Cancer Res; 77(13); 3551-63. ©2017 AACR ., (©2017 American Association for Cancer Research.)

DDR2 mutations occur in approximately 4% of lung squamous cell cancer (SCC) where the tyrosine kinase inhibitor dasatinib has emerged as a new therapeutic option. We found that ERK and AKT phosphorylation was weakly inhibited by dasatinib in DDR2-mutant lung SCC cells, suggesting that dasatinib inhibits survival signals distinct from other oncogenic receptor tyrosine kinases (RTK) and/or compensatory signals exist that dampen dasatinib activity. To gain better insight into dasatinib's action in these cells, we assessed altered global tyrosine phosphorylation (pY) after dasatinib exposure using a mass spectrometry-based quantitative phosphoproteomics approach. Overlaying protein-protein interaction relationships upon this dasatinib-regulated pY network revealed decreased phosphorylation of Src family kinases and their targets. Conversely, dasatinib enhanced tyrosine phosphorylation in a panel of RTK and their signaling adaptor complexes, including EGFR, MET/GAB1, and IGF1R/IRS2, implicating a RTK-driven adaptive response associated with dasatinib. To address the significance of this observation, these results were further integrated with results from a small-molecule chemical library screen. We found that dasatinib combined with MET and insulin-like growth factor receptor (IGF1R) inhibitors had a synergistic effect, and ligand stimulation of EGFR and MET rescued DDR2-mutant lung SCC cells from dasatinib-induced loss of cell viability. Importantly, we observed high levels of tyrosine-phosphorylated EGFR and MET in a panel of human lung SCC tissues harboring DDR2 mutations. Our results highlight potential RTK-driven adaptive-resistant mechanisms upon DDR2 targeting, and they suggest new, rationale cotargeting strategies for DDR2-mutant lung SCC., (©2014 American Association for Cancer Research.)