Abstract
Signal transducer and activator of transcription 4 (STAT4) is a critical transcription factor for T helper cell differentiation and tumor cells. Although its prognostic role and gene function have been reported in several carcinomas, the role of STAT4 in vitro and in vivo in breast cancer remains poorly understood. The effect of STAT4 in immunotherapy is also unclear. Therefore, we integrated bulk transcriptomics, experiments, and single-cell transcriptomics to systematically analyze its function in prognosis and signaling pathway. Several clinical breast cancer cohorts confirmed STAT4 as a T-cell relevant prognostic biomarker. Overexpressed STAT4 increased programmed cell death ligand 1 (PD-L1) and major histocompatibility complex class II levels in breast cancer cells. In molecular mechanism, transcriptional synergy between STAT4 and STAT3 transactivated interleukin (IL)-12R and involved a positive feedback loop: STAT4/IL-12R/JAK2-STAT3-STAT4, which contributed to the upregulation of PD-L1 expression. The above signaling axis was defined as the STAT4-related pathway and its score was used to predict T-cell expansion and anti-PD1 treatment response. These findings highlight a novel molecular mechanism indirectly regulating PD-L1 through the STAT4-related pathway: IL-12R/JAK2-STAT3-STAT4/PD-L1, and it has potential application in predicting anti-PD-1 immunotherapy response, which may pave the way for stratified immunotherapy in breast cancer.