Identification of protein kinase signaling networks activating partial EMT as therapeutic targets in non-small cell lung cancer

Non-small cell lung cancer (NSCLC), of which one-third are lung squamous cell carcinomas (LUSC), is the leading cause of cancer-related death in the US. LUSC treatments primarily involve platinum-based chemotherapy and immune checkpoint blockade. However, only 20% of patients benefit long-term, underscoring a critical need for strategies that improve treatment efficacy. We have identified partial epithelial-to-mesenchymal transition (pEMT) as a key mechanism hindering treatment efficacy in LSCC. pEMT is a cell state in which cancer cells display epithelial and mesenchymal characteristics, and is associated with heightened cell migration/invasion, survival, and treatment resistance. Therefore, we sought to identify phosphorylation networks that could reverse pEMT and, thereby, sensitize LSCC to treatment. We have identified a STE20-family kinase network as a central signaling node sustaining pEMT in LSCC cells. RNAseq analysis of STE20-inhibited LSCC cells revealed transcriptional reprogramming of LSCC indicative of reversion to an epithelial-like phenotype. Consistently, we observed increased expression of epithelial markers (E-cadherin, EpCAM), and reduced levels of mesenchymal markers (vimentin, CD44). Furthermore, STE20 depletion or inhibition suppressed key pEMT functions, including migration, invasion, and clonogenic potential. Our current studies are aimed at identifying the underlying mechanisms of the observed phenotypes. Our initial analysis indicates that STE20 is required for the activation of the YAP/TAZ and MYC transcriptional programs. Last, to lay the groundwork for combination treatments, we conducted a high-throughput screen using a library of clinically relevant compounds in combination with STE20 inhibitors. This screen showed potential synergism with platinum-based chemotherapy, which we are investigating in vitro and in vivo . In conclusion, we have uncovered a STE20 phosphorylation module that sustains pEMT in NSCLC cells and represents an actionable vulnerability that can be targeted to sensitize NSCLCs to first-line treatments.