Inhibition of XBP1s ubiquitination enhances its protein stability and improves glucose homeostasis

BACKGROUND

Hepatic ER stress is a risk factor of insulin resistance and type 2 diabetes. X-box binding protein 1 spliced (XBP1s), a transcription factor, plays a key role in ameliorating insulin resistance and maintaining glucose homeostasis. Unfortunately, the short half-life of the protein dampens its clinical application, and the specific site of lysine residue that could be ubiquitinated and involved in the degradation of XBP1s remains elusive.

METHODS AND RESULTS

Here, we identified K60 and K77 on XBP1s as two pivotal ubiquitin sites required for its proteasome-dependent degradation. We also constructed a double mutant form of XBP1s (K60/77R) and found that it showed higher capacity in resisting against ubiquitin-mediated protein degradation, increasing nuclear translocation, enhancing transcriptional activity, suppressing ER stress and promoting Foxo1 degradation, compared to that of wild type XBP1s (WT). Consistently, overexpression of the K60/77R XBP1s mutant in DIO mice increased the ability to reduce ER stress and decrease Foxo1 levels, thus contributed to maintaining glucose homeostasis.

CONCLUSION

Our results suggest that delaying the degradation of XBP1s by preventing ubiquitination might provide a strategic approach for reducing ER stress as an anti-diabetes therapy.

miR-96 enhances the proliferation of cervical cancer cells by targeting FOXO1

MiRNAs affect various biological pathways associated with the development, progression, clinical outcome and treatment response improvement in cervical cancer. This study was performed to evaluate the effects of miRNA 96 on cervical cancer and to clarify the mechanism. Vivo and vitro experiments were conducted in our trial. MiR-96 is upregulated in cervical cancer cell lines and cervical cancer tissues and is correlated with clinical features in cervical cancer patients. Overexpression of miR-96 enhances proliferation of cervical cancer cells, while inhibiting miR-96 reduces the proliferation of cervical cancer cells. Inhibition of miR-96 significantly decreased the percentage of cells in the S phase and increased the percentage of cells in G1/G0 peak in both SiHa and CaSki cells compared with NC cells and decreased the expressions of p21, p27 and cyclin D1. FOXO1 3'-UTR was sub cloned into a luciferase reporter vector and the putative miR-96 binding site in the FOXO1 3'-UTR was mutated. Treated with miR-96 inhibitor consistently enhanced the luciferase activity of the FOXO1 3'-UTR luciferase reporter plasmids in both SiHa and CaSki cells, whereas mutations in the miR-96-binding site abolished the effect. Vivo experiment also support these results. Therefore, inhibition of miR-96 might suppress growth, proliferation of CC cells and promote apoptosis of CC cells both in vitro and in vivo.

Long non-coding RNA GAS5 promotes osteogenic differentiation of bone marrow mesenchymal stem cells by regulating the miR-135a-5p/FOXO1 pathway

Studies have shown that promoting the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts could protect against osteoporosis. Increasing evidence demonstrates that long non-coding RNAs (lncRNAs) participate in BMSC osteogenic differentiation. This study aimed to investigate the role and underlying mechanism of growth arrest-specific transcript 5 (GAS5) in osteogenic differentiation. The mechanism was mainly focused on miR-135a-5p/FOXO1 pathway by gain- and loss-of function tests. GAS5 and FOXO1 expression was decreased, whereas miR-135a-5p expression was increased, in the BMSCs from osteoporotic mice. Levels of GAS5 and FOXO1 were increased and miR-135a-5p expression was decreased during osteogenic differentiation of BMSCs. Overexpression of GAS5 promoted, whereas knockdown of GAS5 suppressed, BMSC osteogenic differentiation. As for the mechanism, GAS5 functioned as a competing endogenous RNA for miR-135a-5p to regulate FOXO1 expression. In conclusion, GAS5 promoted osteogenesis of BMSCs by regulating the miR-135a-5p/FOXO1 axis. This finding suggests that targeting GAS5 may be a useful therapy for treating postmenopausal osteoporosis.

Spatiotemporal expression and regulation of FoxO1 in mouse uterus during peri-implantation period

Recent studies indicate that FoxO1 has roles in female reproductive system, especially in maternal endometrium. Although various cellular aspects and molecular pathways have been identified, the exact molecular characteristics of embryo implantation are still not completely understood. In this study, we aimed to investigate uterine expression and regulation of FoxO1 during peri-implantation period in mice. Experimental mouse models including, normal pregnancy, pseudopregnancy, artificial decidualization, and delayed implantation and activation were performed. Our results showed that FoxO1 expression was spatiotemporal in mouse endometrial tissue throughout peri-implantation period and its expression was significantly upregulated in luminal and glandular epithelium at the time of implantation. Moreover, on day 5 morning (09:00 AM) of pregnancy, expression of FoxO1 was cytoplasmic in endometrial luminal epithelial cells where embryo homing takes place. With progressing time on day 5 evening (19:00 PM) of pregnancy FoxO1 expression was nuclear in luminal epithelium at implantation site. Pseudopregnancy and artificial decidualization models indicated that FoxO1 expression was regulated by pregnancy hormones. Delayed implantation and activation model indicated that FoxO1 expression at the time of implantation is dependent upon activation status of blastocyst due to E2 induction and uterine sensitivity to implantation. In conclusion, our findings highlight a perspective for FoxO1 expression and regulation in mouse uterus during peri-implantation period indicating that its expression is regulated by implanting embryo and pregnancy hormones.

Impact of silencing hepatic SREBP-1 on insulin signaling

Sterol Regulatory Element Binding Protein-1 (SREBP-1) is a conserved transcription factor of the basic helix-loop-helix leucine zipper family (bHLH-Zip) that plays a central role in regulating expression of genes of carbohydrate and fatty acid metabolism in the liver. SREBP-1 activity is essential for the control of insulin-induced anabolic processes during the fed state. In addition, SREBP-1 regulates expression of key molecules in the insulin signaling pathway, including insulin receptor substrate 2 (IRS2) and a subunit of the phosphatidylinositol 3-kinase (PI3K) complex, PIK3R3, suggesting that feedback mechanisms exist between SREBP-1 and this pathway. Nevertheless, the overall contribution of SREBP-1 activity to maintain insulin signal transduction is unknown. Furthermore, Akt is a known activator of mTORC1, a sensor of energy availability that plays a fundamental role in metabolism, cellular growth and survival. We have silenced SREBP-1 and explored the impact on insulin signaling and mTOR in mice under fed, fasted and refed conditions. No alterations in circulating levels of insulin were observed. The studies revealed that depletion of SREBP-1 had no impact on IRS1Y612, AktS473, and downstream effectors GSK3αS21 and FoxO1S256 during the fed state. Nevertheless, reduced levels of these molecules were observed under fasting conditions. These effects were not associated with changes in phosphorylation of mTOR. Overall, our data indicate that the contribution of SREBP-1 to maintain insulin signal transduction in liver is modest.

MicroRNA-9 promotes the proliferation, migration, and invasion of breast cancer cells via down-regulating FOXO1

PURPOSE

The objective of the study was to investigate the role of microRNA-9 (miR-9) targeting forkhead box O1 (FOXO1) in the proliferation, migration, and invasion of breast cancer cells.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to determine the expressions of miR-9 and FOXO1 mRNA in breast cancer tissues, normal breast tissues, breast cancer cell lines, and normal breast epithelial cells. After the up-regulation of miR-9 expression, qRT-PCR and Western blotting were used to determine the expression of FOXO1. The luciferase reporter gene assay was used to validate the target gene. The CCK-8 assay, scratch-wound healing assay, and Transwell invasion assay were used to investigate the changes in the proliferation, migration, and invasion of breast cancer cells, respectively.

RESULTS

MicroRNA-9 expression was significantly up-regulated in breast cancer tissues and breast cancer cell lines when compared with normal breast tissues and normal breast epithelial cells (both P < 0.05). FOXO1 mRNA and protein expressions were substantially down-regulated in breast cancer tissues and breast cancer cell lines when compared with normal breast tissues and normal breast epithelial cells (both P < 0.05). There can be a negative correlation between miR-9 and FOXO1 mRNA in breast cancer. Luciferase reporter gene assay indicated that miR-9 can down-regulate FOXO1 expression at a post-transcriptional level through binding specifically to FOXO1 3'UTR. The results of CCK-8 assay, scratch-wound healing assay, and Transwell invasion assay revealed that the inhibition of miR-9 can suppress MCF7 cell proliferation, migration, and invasion. Additionally, the expression of miR-9 increased significantly whilst that of FOXO1 decreased substantially as the disease progressed (P < 0.05).

CONCLUSIONS

Our study provides evidence that miR-9 can promote the proliferation, migration, and invasion of breast cancer cells via down-regulating FOXO1.