Superoxide Dismutase-3 Downregulates Laminin α5 Expression in Tumor Endothelial Cells via the Inhibition of Nuclear Factor Kappa B Signaling

SIMPLE SUMMARY: Tumor-infiltrating lymphocytes determine cancer prognosis and the response to immunotherapy. The balance of laminin-α4/laminin-α5 isoforms in the endothelial basement membrane plays an instructive function in regulating the diapedesis of immune cells under inflammatory conditions. Previous studies showed that the extracellular superoxide dismutase (SOD)3 induces laminin-α4, which is associated with improved disease-free survival of colorectal cancer patients. The aim of our study was to determine whether SOD3 also affects the expression of laminin-α5 in the tumor vasculature. The results showed that SOD3 differentially regulates laminin-α4 and laminin-α5 in the tumor endothelium. SOD3 promoted notable transcriptomic changes in tumor-stimulated endothelial cells, including the inhibition of the nuclear factor kappa B (NF-κB) pathway, an inductor of laminin α5 transcription. Therefore, high SOD3 levels in the tumor vasculature shifted the laminin α4/α5 balance towards the laminin-α4(high)/laminin-α5(low) phenotype, which is permissive for T cell diapedesis into tumors and explains the improved cancer immune surveillance associated to high SOD3 levels. ABSTRACT: The balance between laminin isoforms containing the α5 or the α4 chain in the endothelial basement membrane determines the site of leukocyte diapedesis under inflammatory conditions. Extracellular superoxide dismutase (SOD3) induces laminin α4 expression in tumor blood vessels, which is associated with enhanced intratumor T cell infiltration in primary human cancers. We show now that SOD3 overexpression in neoplastic and endothelial cells (ECs) reduces laminin α5 in tumor blood vessels. SOD3 represses the laminin α5 gene (LAMA5), but LAMA5 expression is not changed in SOD1-overexpressing cells. Transcriptomic analyses revealed SOD3 overexpression to change the transcription of 1682 genes in ECs, with the canonical and non-canonical NF-κB pathways as the major SOD3 targets. Indeed, SOD3 reduced the transcription of well-known NF-κB target genes as well as NF-κB-driven promoter activity in ECs stimulated with tumor necrosis factor (TNF)-α, an NF-κB signaling inducer. SOD3 inhibited the phosphorylation and degradation of IκBα (nuclear factor of the kappa light polypeptide gene enhancer in B-cells inhibitor alpha), an NF-κB inhibitor. Finally, TNF-α was found to be a transcriptional activator of LAMA5 but not of LAMA4; LAMA5 induction was prevented by SOD3. In conclusion, SOD3 is a major regulator of laminin balance in the basement membrane of tumor ECs, with potential implications for immune cell infiltration into tumors.