Expression of PVRL4, a molecular target for cancer treatment, is transcriptionally regulated by FOS.

PVRL4 (or nectin­4) is a promising therapeutic target since its upregulated expression is found in a wide range of human cancer types. Enfortumab vedotin, an antibody­drug conjugate targeting PVRL4, is clinically used for the treatment of urothelial bladder cancer. In addition, rMV­SLAMblind, a genetically engineered oncolytic measles virus, can infect cancer cells and induce apoptosis through interaction with PVRL4. Although PVRL4 transcript levels are elevated in breast, lung and ovarian cancer, the mechanisms of its upregulation have not yet been uncovered. To clarify the regulatory mechanisms of elevated PVRL4 expression in breast cancer cells, Assay for Transposase­Accessible Chromatin­sequencing and chromatin immunoprecipitation­sequencing (ChIP­seq) data were used to search for its regulatory regions. Using breast cancer cells, an enhancer region was ultimately identified. Additional analyses, including ChIP and reporter assays, demonstrated that FOS interacted with the PVRL4 enhancer region, and that alterations of the FOS­binding motifs in the enhancer region decreased reporter activity. Consistent with these data, exogenous expression of FOS enhanced the reporter activity and PVRL4 expression in breast cancer cells. Furthermore, RNA­seq analysis using breast cancer cells treated with PVRL4 small interfering RNA revealed its possible involvement in the cytokine response and immune system. These data suggested that FOS was involved, at least partly, in the regulation of PVRL4 expression in breast cancer cells, and that elevated PVRL4 expression may regulate the response of cancer cells to cytokines and the immune system.