Abstract 142: Integrin α6β4 upregulates IDO1 expression and decreases IFNγ-mediated T cell growth in ER-negative breast cancer

Abstract The kynurenine metabolic pathway degrades tryptophan into immunosuppressive metabolites following pro-inflammatory cytokine stimulation and is upregulated in ER-negative (ER(-)) breast cancers, where it is associated with a worse prognosis. The laminin receptor integrin α6β4 is expressed in a majority of hormone receptor negative breast cancers, where it is known to promote an aggressive phenotype by regulating cellular signaling and epigenetics. Here, we seek to identify how integrin α6β4 regulates the IFNγ-mediated induction of the first kynurenine pathway enzyme, IDO1, and its impact on immunosuppression in ER(-) breast cancer. Integrin β4 only pairs with integrin α6; thus, expression of the β4 subunit is representative of integrin α6β4 when integrin α6 is expressed. We demonstrate that stable expression of integrin β4 in BT549 cells regulates IDO1 expression by altering methylation of the IDO1 promoter and gene body compared to empty vector (EV) control, which resulted in increased IDO1 expression determined using high throughput sequencing, qPCR, and immunoblot analyses. Likewise, knockdown of integrin β4 by shRNA or knockout by CRISPR in HCC1806 and HCC1954 cells decreased IDO1 expression. Gene set enrichment analysis demonstrated an increased IFNγ response in BT549 cells expressing integrin β4 compared to EV control. Moreover, using the TCGA Breast Invasive Carcinoma dataset, we show that expression of IFNγ, a known inducer of IDO1, is positively associated with IDO1 expression in breast cancer. Upon IFNγ stimulation, the expression of integrin β4 resulted in a more dramatic upregulation of IDO1 at the mRNA and protein level, which was accompanied by alterations in STAT signaling. Furthermore, integrin α6β4 signaling significantly increased secretion of the immunosuppressive metabolite kynurenine following IFNγ stimulation, effects which were abrogated by pharmacologic IDO1 inhibition. Using conditioned media transfer onto Jurkat cells, we show that conditioned media from integrin β4-expressing cells stimulated with IFNγ significantly reduced T cell growth compared to media from IFNγ stimulated EV cells or unstimulated β4 cells. In summary, our data suggest that integrin α6β4 increases IDO1 induction in ER(-) breast cancer cells, amplifies kynurenine secretion, and suppresses T cell growth in the presence of the inflammatory cytokine IFNγ. This study suggests a novel role of integrin α6β4 in limiting T cell-mediated antitumor immunity and highlights the need to elucidate the detailed mechanisms governing integrin α6β4-mediated immunosuppression in ER(-) breast cancers. Citation Format: Parvanee Karimpour, Oscar Hanson, Andrew Elliott, Min Chen, Kathleen O'Connor. Integrin α6β4 upregulates IDO1 expression and decreases IFNγ-mediated T cell growth in ER-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 142.