PTPRJ-Targeting Peptide Agonist Induces Broad Cellular Signaling Perturbations and DNA Damage in Lung Cancer Cells

Receptor protein tyrosine phosphatases (RPTPs) are key regulators of cell signaling. However, their study and therapeutic targeting have been limited by the lack of known natural ligands or selective agonists, as well as an incomplete understanding of their structure-function relationships. Nonetheless, receptor homodimerization has been shown to suppress RPTP catalytic activity by restricting substrate access, offering a promising strategy for examining and modulating their function. Our previous work on PTPRJ, a member of the RPTP family, showed that its transmembrane domain regulates homodimerization, thereby controlling access to receptor tyrosine kinase (RTK) substrates and their phosphorylation levels. We also developed peptides that disrupt this dimerization, thereby inhibiting RTK phosphorylation and reducing cancer cell migration. These peptides were then engineered for selective, pH-sensitive insertion into the acidic tumor microenvironment to enhance efficacy while limiting off-target effects. Yet how broadly PTPRJ activation reshapes the phosphotyrosine landscape and whether those changes yield coherent cellular phenotypes remains unclear. In this study, we employed tyrosine phosphoproteomics, immunoblotting, immunofluorescence, and functional assays to assess the global impact of our lead peptide candidate, Hybrid 7, in A549 lung cancer cells that endogenously express PTPRJ. We find that Hybrid 7 decreases EGFR phosphorylation and selectively reduces phosphorylation across additional RTKs and motility adaptors, producing strong inhibition of EGF-driven migration and reduced proliferation. Hybrid 7 also elevates reactive oxygen species and DNA damage, and enforces CDK1-dependent G2/M arrest, indicating a primarily cytostatic, checkpoint-mediated response. These findings highlight the potential of RPTP-targeting peptides as valuable tools for dissecting RPTP function and as possible therapeutic agents capable of modulating key oncogenic pathways and inhibiting cancer progression.