Differential function and regulation of orphan nuclear receptor TR3 isoforms in endothelial cells

PIK3Cδ expression by fibroblasts promotes triple-negative breast cancer progression

As there is growing evidence for the tumor microenvironment's role in tumorigenesis, we investigated the role of fibroblast-expressed kinases in triple-negative breast cancer (TNBC). Using a high-throughput kinome screen combined with 3D invasion assays, we identified fibroblast-expressed PIK3Cδ (f-PIK3Cδ) as a key regulator of cancer progression. Although PIK3Cδ was expressed in primary fibroblasts derived from TNBC patients, it was barely detectable in breast cancer (BC) cell lines. Genetic and pharmacological gain- and loss-of-function experiments verified the contribution of f-PIK3Cδ in TNBC cell invasion. Integrated secretomics and transcriptomics analyses revealed a paracrine mechanism via which f-PIK3Cδ confers its protumorigenic effects. Inhibition of f-PIK3Cδ promoted the secretion of factors, including PLGF and BDNF, that led to upregulation of NR4A1 in TNBC cells, where it acts as a tumor suppressor. Inhibition of PIK3Cδ in an orthotopic BC mouse model reduced tumor growth only after inoculation with fibroblasts, indicating a role of f-PIK3Cδ in cancer progression. Similar results were observed in the MMTV-PyMT transgenic BC mouse model, along with a decrease in tumor metastasis, emphasizing the potential immune-independent effects of PIK3Cδ inhibition. Finally, analysis of BC patient cohorts and TCGA data sets identified f-PIK3Cδ (protein and mRNA levels) as an independent prognostic factor for overall and disease-free survival, highlighting it as a therapeutic target for TNBC.

Orphan nuclear receptor TR3/Nur77 biologics inhibit tumor growth by targeting angiogenesis and tumor cells

Pathological angiogenesis is a hallmark of many diseases. Previously, we reported that orphan nuclear receptor TR3/Nur77 was a critical mediator of angiogenesis to regulate tumor growth, sepsis and skin wound healing. However, none of the TR3/Nur77 targeting molecule has been in clinical trial so far. Here, we designed and generated novel TR3 shRNAs and two minigenes that had therapeutic potential for cancer treatment. In addition to extend our previous findings that tumor growth was inhibited in Nur77 knockout mice, we found that metastasis of colorectal tumor was completely inhibited in Nur77-/- mice. Tumor masses were increased ~70% and decreased ~40% in our transgenic EC-Nur77-S mice and EC-Nur77-DN mice, in which the full-length cDNA and the dominant negative mutant of TR3/Nur77 were inducibly and specifically expressed in mouse endothelium, respectively. TR3 was highly expressed in the vasculature and tumor cells of human melanoma and colorectal cancer tissues, but not in normal tissues. The novel TR3 shRNAs and two minigenes almost completely inhibited the proliferation and migration of HUVECs and human melanoma A375sm cells. Angiogenesis induced by adenoviruses expressing VEGF and melanoma growth in mice were greatly and significantly inhibited by systemically administration of adenoviruses expressing TR3 shRNAs and two minigenes. Tumor angiogenesis and the expressions of genes associated with angiogenesis were greatly regulated in tumor tissues treated with TR3 shRNAs and minigenes. Taken together, these studies demonstrated that TR3/Nur77 was a specific therapeutic target for several human cancers by targeting both tumor cells and tumor microenvironment. These TR3/Nur77 biologics inhibit angiogenesis and tumor growth, and have translational potential.

The involvement of NR4A1 and NR4A2 in the regulation of the luteal function in rats

The nuclear receptor 4A (NR4A) members play important roles in cellular proliferation, differentiation and apoptosis. The current study first evaluate the expression of ovarian NR4A1 during different luteal stages in rats. Immature rats aged 28 days were treated with sequential Pregnant mare serum gonadotropin (PMSG) (D -2) / human chorionic gonadotropin (hCG) (D 0) to induce pseudopregnancy. Serum progesterone (P₄) and ovarian expression of NR4A1 were detected by RIA and WB, respectively, at follicle stage (D 0), early (D 2), middle (D 7) and late (D 14 and D 20) luteal stages. To confirm the role of NR4A1 during the luteal regression, rats were treated with prostaglandin F_2α analog (PGF) for 0-8 h on D 7 to detect the expressions of NR4A1 and NR4A2. RIA result showed that serum P₄ reached highest level on D 7 and then declined. WB results showed that there were two types of NR4A1 (NR4A1-L and NR4A1-S) expressed in the ovary. The ovarian NR4A1-L decreased at the late luteal stage (D 20). However, the NR4A1-S increased at the late luteal stage (D 14). After PGF treatment on D 7, the expression of NR4A1-S increased which peaked at 0.5-1 h and then declined; while NR4A1-L expression did not change within 8 h. Real-time PCR results showed that the ovarian NR4A1 mRNA increased within 0.5 h, maintained high at 1 h and then declined. The NR4A2 mRNA expression exhibited a similar pattern to that of NR4A1 mRNA, though its abundance was not as high as NR4A1. IHC results revealed that NR4A1-L was expressed mainly in the cytoplasm of luteal steroidogenic cells, faintly expressed in the follicle theca cells, oocytes and the pericytes; while NR4A2 was primarily localized in the cytoplasm of luteal steroidogenic cells. In conclusion, all these results demonstrate that NR4A2 as well as NR4A1 might be involved in the luteal development and luteolysis in rats.