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The molecular mechanisms allowing hair follicles to periodically activate their stem cells (HFSCs) are incompletely characterized. Here, we identify the transcription factor IRX5 as a promoter of HFSC activation. Irx5-/- mice have delayed anagen onset, with increased DNA damage and diminished HFSC proliferation. Open chromatin regions form near cell cycle progression and DNA damage repair genes in Irx5-/- HFSCs. DNA damage repair factor BRCA1 is an IRX5 downstream target. Inhibition of FGF kinase signaling partially rescues the anagen delay in Irx5-/- mice, suggesting that the Irx5-/- HFSC quiescent phenotype is partly due to failure to suppress Fgf18 expression. Interfollicular epidermal stem cells also show decreased proliferation and increased DNA damage in Irx5-/-mice. Consistent with a role for IRX5 as a promoter of DNA damage repair, we find that IRX genes are upregulated in many cancer types and that there is a correlation between IRX5 and BRCA1 expression in breast cancer.

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third most frequent cause of cancer-related death. The IRX5 transcription factor plays a different role in multiple cancers and contributes to the development of many tumours. However, little is known about the molecular mechanisms of IRX5 in HCC. In this study, we found that IRX5 was abnormally upregulated in HCC tissues compared with adjacent normal tissues. IRX5 promoted HCC cell proliferation and upregulated the expression of cyclin D1 and knockdown of IRX5 suppressed tumorigenicity in vivo. Furthermore, knockdown of IRX5 increased p53 and Bax expression and decreased Bcl-2 expression. Thus, IRX5 suppressed apoptosis in HCC cells by inhibiting the p53 signalling pathway, indicating its role as a treatment target for HCC. SIGNIFICANCE OF THE STUDY: Our study demonstrated that IRX5 was abnormally upregulated in HCC tissues compared with adjacent normal tissues. IRX5 promoted HCC cell proliferation and upregulated the expression of cyclin D1, and knockdown of IRX5 suppressed tumorigenicity in vivo. Furthermore, knockdown of IRX5 increased p53 and Bax expression and decreased Bcl-2 expression. IRX5 suppressed apoptosis in HCC cells by inhibiting the p53 signalling pathway, indicating its role as a treatment target for HCC.

Background/Aims: The long-noncoding RNA colorectal neoplasia differentially expressed (CRNDE) gene was first found to be activated in colorectal neoplasia. Now, it also has been found to be upregulated in many other solid tumors. Whether CRNDE affects tumorigenesis remains unknown. Methods: We conducted bioinformatics, real-time polymerase chain reaction (PCR), Western blot analysis, cell proliferation assay, colony formation assay, wound healing assay, cell migration and invasion assays, RNA immunoprecipitation, and reporter vector construction and luciferase assays. Results: CRNDE was upregulated in hepatocellular carcinoma (HCC). The overexpression of CRNDE promoted HCC cellular proliferation, migration, and invasion in intro and in vivo, and acted as an oncogene in HCC progression. Furthermore, CRNDE impaired miR-136-5P expression in a RISC manner, and a reciprocal repression feedback loop was possible between CRNDE and miR-136-5P. We found that the neighboring mRNA of CRNDE was IRX5, and IRX5 increased the tumorigenicity of HCC cells. IRX5 was a potential downstream target gene of miR-136-5P. MiR-136 regulated IRX5 by interacting with its 3’UTR. In addition, miR-136-5P was involved in the CRNDE-regulated expression of IRX5. Conclusion: CRNDE acted as a tumor oncogene by exhibiting oncogenic properties of human HCC and revealed a novel CRNDE-miR-136-5P-IRX5 regulatory network in HCC. CRNDE may be considered to be a potential target for HCC therapies based on its ability to upregulate IRX5, and it deserves further investigation.

Objective A causal obesity risk variant in the FTO locus was recently shown to inhibit adipocyte thermogenesis via increased adipose expression of the homeobox transcription factors IRX3 and IRX5. However, causal effects of IRX5 on fat storage remain to be shown in vivo, and discovery of downstream mediators may open new therapeutic avenues. Methods 17 WT and 13 Irx5 knockout (KO) mice were fed low-fat control (Ctr) or high-fat (HF) diet for 10 weeks. Body weight, energy intake and fat mass were measured. Irx5-dependent gene expression was explored by transcriptome analysis of epididymal white adipose tissue (eWAT), confirmatory obesity-dependent expression in human adipocytes in vivo, and in vitro knock-down, overexpression and transcriptional activation assays. Results Irx5 knock-out mice weighed less, had diminished fat mass, and were protected from diet-induced fat accumulation. Key adipose mitochondrial genes Pparγ coactivator 1-alpha (Pgc-1α) and uncoupling protein 1 (Ucp1) were upregulated, and a gene network centered on amyloid precursor protein (App) was downregulated in adipose tissue of knock-out mice and in isolated mouse adipocytes with stable Irx5 knock-down. An APP-centered network was also enriched in isolated adipocytes from obese compared to lean humans. IRX5 overexpression increased APP promoter activity and both IRX5 and APP inhibited transactivation of PGC-1α and UCP1. Knock-down of Irx5 or App increased mitochondrial respiration in adipocytes. Conclusion Irx5-KO mice were protected from obesity and this can partially be attributed to reduced adipose App and improved mitochondrial respiration. This novel Irx5-App pathway in adipose tissue is a possible therapeutic entry point against obesity.

In the mouse retina, at least ten distinct types of bipolar interneurons are involved in the transmission of visual signals from photoreceptors to ganglion cells. How bipolar interneuron diversity is generated during retinal development is poorly understood. Here, we show that Irx5, a member of the Iroquois homeobox gene family, is expressed in developing bipolar cells starting at postnatal day 5 and is localized to a subset of cone bipolar cells in the mature mouse retina. In Irx5-deficient mice, defects were observed in the expression of some, but not all, immunohistological markers that define mature Type 2 and Type 3 OFF cone bipolar cells, indicating a role for Irx5 in bipolar cell differentiation. The differentiation of these two bipolar cell types has previously been shown to require the homeodomain-CVC transcription factor, Vsx1. However, the defects observed in Irx5-deficient retinas do not coincide with a reduction of Vsx1 expression, and conversely, the expression of Irx5 in cone bipolar cells does not require the presence of a functional Vsx1 allele. These results indicate that there are at least two distinct genetic pathways (Irx5-dependent and Vsx1-dependent) regulating the development of Type 2 and Type 3 cone bipolar cells.