Jun is a key Regulator of Prostate Cancer Progression and Immune Microenvironment Dynamics
Background: Prostate cancer remains one of the most diagnosed malignancies among men worldwide and is responsible for significant morbidity and mortality. Despite advances in diagnostics and therapeutics, effective management and understanding of its molecular biology continue to pose challenges. The disease develops through malignant transformation of the prostate epithelium in a stepwise, mutation-driven process. Although AP1 transcription factors have been implicated as presumed oncogenic drivers, the molecular programs contributing to prostate cancer progression are still not fully understood. Methods: To investigate the role of the AP1 transcription factor Jun in prostate cancer, we deleted Jun in a Pten deficient PCa mouse model.  We performed RNAseq analysis of sorted epithelial cells and immune-phenotyped the tumors of different genotypes by immunohistochemistry methods. We compared the results from the in vivo model to publicly available human expression datasets and prostate cancer tissue microarrays.  Results Decreased JUN expression levels corresponded with advanced stages of prostate cancer, effectively distinguishing high and low-risk human prostate tumors. Surprisingly, Jun expression was significantly increased in a Pten-deficient prostate cancer mouse model, recapitulating early stages of PCa development. Immune phenotyping of Pten-deficient prostates revealed high accumulation of tumor-infiltrating leukocytes, particularly innate immune cells, neutrophils and macrophages as well as high levels of Stat3 activation (pStat3Tyr705) and Il1-ß production. Remarkably, Jun depletion prevented immune cell attraction accompanied by significantly reduced levels of pStat3Tyr705 and Il1-ß production and accelerated growth of Jun/Pten-deficient (JunPE?/?;PtenPE?/?) tumors. Comparative whole transcriptome profiling of prostate epithelial cells revealed a SenMayo senescence associated gene signature, upregulation of pro-inflammatory processes and cytokines such as Il1b, Ccl3 and Ccl8 that are pivotal for immune cell attraction in Pten-deficient prostates. Strikingly, depletion of Jun reversed both senescence and senescence-associated immune infiltration and, as a consequence, further accelerated tumor expansion. Overall design: EPCAM expressing cells of murine prostates of wildtype (wt) mice and mice with probasin (Pb) promoter-controlled Cre-mediated homozygous deletion of Jun (exon 1) and Pten (exons 4-5) and combined deletion of Jun and Pten were enriched by MACS sorting, collected and subjected to RNA extraction. Libraries yield from 200 ng of high-quality RNA were subjected to 75bp single-end sequencing.