Mxi1 regulates cell proliferation through insulin-like growth factor binding protein-3

A single-cell transcriptome of mesenchymal stromal cells to fabricate bioactive hydroxyapatite materials for bone regeneration

The osteogenic microenvironment of bone-repairing materials plays a key role in accelerating bone regeneration but remains incompletely defined, which significantly limits the application of such bioactive materials. Here, the transcriptional landscapes of different osteogenic microenvironments, including three-dimensional (3D) hydroxyapatite (HA) scaffolds and osteogenic medium (OM), for mesenchymal stromal cells (MSCs) in vitro were mapped at single-cell resolution. Our findings suggested that an osteogenic process reminiscent of endochondral ossification occurred in HA scaffolds through sequential activation of osteogenic-related signaling pathways, along with inflammation and angiogenesis, but inhibition of adipogenesis and fibrosis. Moreover, we revealed the mechanism during OM-mediated osteogenesis involves the ZBTB16 and WNT signaling pathways. Heterogeneity of MSCs was also demonstrated. In vitro ossification of LRRC75A⁺ MSCs was shown to have better utilization of WNT-related ossification process, and PCDH10⁺ MSCs with superiority in hydroxyapatite-related osteogenic process. These findings provided further understanding of the cellular activity modulated by OM conditions and HA scaffolds, providing new insights for the improvement of osteogenic biomaterials. This atlas provides a blueprint for research on MSC heterogeneity and the osteogenic microenvironment of HA scaffolds and a database reference for the application of bioactive materials for bone regeneration.

Mxi1-0 regulates the growth of human umbilical vein endothelial cells through extracellular signal-regulated kinase 1/2 (ERK1/2) and interleukin-8 (IL-8)-dependent pathways

Mxi1 plays an important role in the regulation of cell proliferation. Mxi1-0, a Mxi1 isoform, has a different N-terminal amino acid sequence, intracellular location and expression profile from Mxi1. However, the precise role of Mxi1-0 in cell proliferation and the molecular mechanism underlying its function remain poorly understood. Here, we showed that Mxi1-0 suppression decreased the proliferation of human umbilical vein endothelial cells (HUVECs) along with cell accumulation in the G2/M phase. Mxi1-0 suppression also significantly decreased the expression and secretion of interleukin (IL-8). Neutralizing IL-8 in conditioned medium (CM) from Mxi1-0-overexpressed HUVECs significantly eliminated CM-induced proliferation of HUVECs. In addition, Mxi1-0 suppression significantly decreased the activity of MAP kinase ERK1/2. Treatment of HUVECs with U0126, an ERK1/2 signaling inhibitor, attenuated autocrine production of IL-8 induced by Mxi1-0 overexpression. On the other hand, Mxi1-0 overexpression-induced IL-8 increased the level of phosphorylated ERK1/2 in HUVECs, and such increasing was diminished in cells incubated with CM, which neutralized with anti-IL-8 antibody. Taken together, our results suggest that Mxi1-0 regulates the growth of HUVECs via the IL-8 and ERK1/2 pathways, which apparently reciprocally activate each other.

Inactivation of max-interacting protein 1 induces renal cilia disassembly through reduction in levels of intraflagellar transport 20 in polycystic kidney

Cilia in ciliated cells consist of protruding structures that sense mechanical and chemical signals from the extracellular environment. Cilia are assembled with variety molecules via a process known as intraflagellar transport (IFT). What controls the length of cilia in ciliated cells is critical to understand ciliary disease such as autosomal dominant polycystic kidney disease, which involves abnormally short cilia. But this control mechanism is not well understood. Previously, multiple tubular cysts have been observed in the kidneys of max-interacting protein 1 (Mxi1)-deficient mice aged 6 months or more. Here, we clarified the relationship between Mxi1 inactivation and cilia disassembly. Cilia phenotypes were observed in kidneys of Mxi1-deficient mice using scanning electron microscopy to elucidate the effect of Mxi1 on renal cilia phenotype, and cilia disassembly was observed in Mxi1-deficient kidney. In addition, genes related to cilia were validated in vitro and in vivo using quantitative PCR, and Ift20 was selected as a candidate gene in this study. The length of cilium decreased, and p-ERK level induced by a cilia defect increased in kidneys of Mxi1-deficient mice. Ciliogenesis of Mxi1-deficient mouse embryonic fibroblasts (MEFs) decreased, and this abnormality was restored by Mxi1 transfection in Mxi1-deficient MEFs. We confirmed that ciliogenesis and Ift20 expression were regulated by Mxi1 in vitro. We also determined that Mxi1 regulates Ift20 promoter activity via Ets-1 binding to the Ift20 promoter. These results indicate that inactivating Mxi1 induces ciliary defects in polycystic kidney.

miR-24-3p and miR-27a-3p promote cell proliferation in glioma cells via cooperative regulation of MXI1

MicroRNAs (miRNAs) are small, non‑coding RNAs which regulate gene expression at the post-transcriptional level. Abnormal expression of miRNAs occurs frequently in tumors. Although the two miRNAs miR‑24‑3p and miR‑27a‑3p come from two duplicated gene clusters of miR‑23a~27a~24‑2 and miR‑23b~27b~24‑1 which are found to be deregulated in a variety of cancers, the role of cooperation of the two clusters and the function of the two miRNAs in tumors have not been completely characterized. Here, we show that overexpression of miR‑24‑3p and miR‑27a‑3p could promote cell proliferation using the MTT assay. By integrated bioinformatic analysis and experimental confirmation, we identified MXI1, which has been found to act as a tumor suppressor gene by affecting c‑Myc, as a direct target of miR‑24‑3p and miR‑27a‑3p. While targeting the MXI1 3' untranslated region by miR‑24‑3p or miR‑27a‑3p, luciferase activity was attenuated. The two miRNAs promote glioma cell proliferation via targeting MXI1 and the experiment was confirmed by the rescue experiments. Furthermore, our results show that two clusters of miR-23a~27a~24-2 and miR‑23b~27b~24‑1 regulate MXI1 synergistically. These findings reveal, for the first time, the novel functions of cooperation of miR‑24‑3p and miR‑27a‑3p from two clusters in promoting cell proliferation through MXI1. Additionally, we observed that miR‑27a‑3p is upregulated in glioma tissues.