Pharmacological doses of all-trans retinoic acid promote G0/G1 transition and G1 arrest of normal human marrow CD34+ cells

Stabilization of β-Catenin Directs HEB to Limit Thymic Selection

Activation of β-catenin in CD4+CD8+ double-positive (DP) thymocytes halts development before the thymic selection stage and predisposes to transformation. Leukemogenesis, but not the developmental block, depends on TCF-1, β-catenin's DNA-binding partner. In this study, we show that β-catenin activation directs the DNA-binding protein HEB to block DP thymocyte development. Conditional loss of HEB in DP thymocytes with stabilized β-catenin restores the frequencies of postselection TCRβhi/CCR7+ and TCRβhi/CD69+ DPs and their cell-cycle profile. This recovery is associated with significant reversal of β-catenin-induced expression changes, particularly those related to the CD69+ DP cell signature and to cell-cycle pathways. Stabilizing β-catenin in DP thymocytes directs HEB binding to ≈11,000 novel DNA sites throughout the genome. Novel HEB sites mark most CD69+ DP cell signature genes that change expression upon activation of β-catenin and then revert after loss of HEB. Moreover, many of the novel HEB sites occupy promoter regions of genes enriched in mitotic cell cycle pathways. HEB binding to those regions correlates with downregulation of the associated genes, and HEB inactivation restores expression to physiologic levels. These findings highlight a molecular interplay between HEB and β-catenin that can impair thymic development.

miRNA-451a regulates RPE function through promoting mitochondrial function in proliferative diabetic retinopathy

The purpose of this study was to explore the role of microRNA-451a (miR-451a) in diabetic retinopathy through activating transcription factor 2 (ATF2). The epiretinal membrane samples from patients with proliferative diabetic retinopathy (PDR) were immunolabeled with an antibody for Ki-67 to identify the proliferative cells. The expression of miR-451a was measured by qRT-PCR in the retina of Akita mice and in RPE cells under diabetic conditions. The potential downstream targets of miR-451a were predicted by bioinformatics and confirmed by dual luciferase assay, qRT-PCR, and Western blotting. Mitochondrial function, cell proliferation, and migration assays were used to detect the functional change after transfection of miR-451a mimic and inhibitor. Proliferative RPE cells were identified in the epiretinal membrane from PDR patients. The expression of miR-451a was downregulated both in the retina of Akita mice and 4-hydroxynonenal (4-HNE)-treated RPE cells. Bioinformatic analysis and luciferase assay identified ATF2 as a potential target of miR-451a. miR-451a inhibited proliferation and migration of RPE cells. The mitochondrial function was enhanced by miR-451a mimic, but suppressed by miR-451a inhibitor. In diabetic conditions, miR-451a showed a protective effect on mitochondrial function. The results of qRT-PCR and Western blotting revealed that overexpression of miR-451a downregulated the expression of ATF2 and its downstream target genes CyclinA1, CyclinD1, and MMP2. In conclusion, miR-451a/ATF2 plays a vital role in the regulation of proliferation and migration in RPE cells through regulation of mitochondrial function, which may provide new perspectives for developing effective therapies for PDR.

STIM1 deficiency is linked to Alzheimer's disease and triggers cell death in SH-SY5Y cells by upregulation of L-type voltage-operated Ca2+ entry

Abstract

STIM1 is an endoplasmic reticulum protein with a role in Ca²⁺ mobilization and signaling. As a sensor of intraluminal Ca²⁺ levels, STIM1 modulates plasma membrane Ca²⁺ channels to regulate Ca²⁺ entry. In neuroblastoma SH-SY5Y cells and in familial Alzheimer’s disease patient skin fibroblasts, STIM1 is cleaved at the transmembrane domain by the presenilin-1-associated γ-secretase, leading to dysregulation of Ca²⁺ homeostasis. In this report, we investigated expression levels of STIM1 in brain tissues (medium frontal gyrus) of pathologically confirmed Alzheimer’s disease patients, and observed that STIM1 protein expression level decreased with the progression of neurodegeneration. To study the role of STIM1 in neurodegeneration, a strategy was designed to knock-out the expression of STIM1 gene in the SH-SY5Y neuroblastoma cell line by CRISPR/Cas9-mediated genome editing, as an in vitro model to examine the phenotype of STIM1-deficient neuronal cells. It was proved that, while STIM1 is not required for the differentiation of SH-SY5Y cells, it is absolutely essential for cell survival in differentiating cells. Differentiated STIM1-KO cells showed a significant decrease of mitochondrial respiratory chain complex I activity, mitochondrial inner membrane depolarization, reduced mitochondrial free Ca²⁺ concentration, and higher levels of senescence as compared with wild-type cells. In parallel, STIM1-KO cells showed a potentiated Ca²⁺ entry in response to depolarization, which was sensitive to nifedipine, pointing to L-type voltage-operated Ca²⁺ channels as mediators of the upregulated Ca²⁺ entry. The stable knocking-down of CACNA1C transcripts restored mitochondrial function, increased mitochondrial Ca²⁺ levels, and dropped senescence to basal levels, demonstrating the essential role of the upregulation of voltage-operated Ca²⁺ entry through Ca_v1.2 channels in STIM1-deficient SH-SY5Y cell death.

Key messages

STIM1 protein expression decreases with the progression of neurodegeneration in Alzheimer’s disease.

STIM1 is essential for cell viability in differentiated SH-SY5Y cells.

STIM1 deficiency triggers voltage-regulated Ca²⁺ entry-dependent cell death.

Mitochondrial dysfunction and senescence are features of STIM1-deficient differentiated cells.

Electronic supplementary material

The online version of this article (10.1007/s00109-018-1677-y) contains supplementary material, which is available to authorized users.

Flow cytometric quantification of all phases of the cell cycle and apoptosis in a two-color fluorescence plot

An optimal technology for cell cycle analysis would allow the concomitant measurement of apoptosis, G0, G1, S, G2 and M phases in combination with cell surface phenotyping. We have developed an easy method in flow cytometry allowing this discrimination in an only two-color fluorescent plot. It is based on the concomitant use of 7-amino-actinomycin D and the antibodies anti-Ki67 and anti-phospho(Ser10)-histone H3, both conjugated to Alexa Fluor®488 to discriminate G0 and M phases, respectively. The method is particularly valuable in a clinical setting as verified in our laboratory by analyzing human leukemic cells from marrow samples or after exposure to cell cycle modifiers.