DIXDC1 Promotes Retinoic Acid-Induced Neuronal Differentiation and Inhibits Gliogenesis in P19 Cells

Suppressor of Fused Regulation of Hedgehog Signaling is Required for Proper Astrocyte Differentiation

Hedgehog signaling is essential for vertebrate development; however, less is known about the negative regulators that influence this pathway. Using the mouse P19 embryonal carcinoma cell model, suppressor of fused (SUFU), a negative regulator of the Hedgehog (Hh) pathway, was investigated during retinoic acid (RA)-induced neural differentiation. We found Hh signaling increased activity in the early phase of differentiation, but was reduced during terminal differentiation of neurons and astrocytes. This early increase in pathway activity was required for neural differentiation; however, it alone was not sufficient to induce neural lineages. SUFU, which regulates signaling at the level of Gli, remained relatively unchanged during differentiation, but its loss through CRISPR-Cas9 gene editing resulted in ectopic expression of Hh target genes. Interestingly, these SUFU-deficient cells were unable to differentiate toward neural lineages without RA, and when directed toward these lineages, they showed delayed and decreased astrocyte differentiation; neuron differentiation was unaffected. Ectopic activation of Hh target genes in SUFU-deficient cells remained throughout RA-induced differentiation and this was accompanied by the loss of Gli3, despite the presence of the Gli3 message. Thus, the study indicates the proper timing and proportion of astrocyte differentiation requires SUFU, likely acting through Gli3, to reduce Hh signaling during late-stage differentiation.

DIXDC1 promotes the growth of acute myeloid leukemia cells by upregulating the Wnt/β-catenin signaling pathway

Accumulating evidence suggests that dysregulation of Dishevelled-Axin domain-containing 1 (DIXDC1) is involved in the progression and development of various cancers. However, little is known about the relevance of DIXDC1 in acute myeloid leukemia (AML). In this study, we aimed to investigate the expression status and potential biological function of DIXDC1 in AML. Our results showed that DIXDC1 expression was highly upregulated in AML cell lines and primary AML blasts compared with normal blasts. Knockdown of DIXDC1 by siRNA-mediated gene silencing significantly inhibited proliferation, induced cell cycle arrest, and promoted apoptosis of AML cells in vitro. By contrast, DIXDC1 overexpression promoted proliferation, accelerated cell cycle progression, and reduced apoptosis of AML cells. Moreover, we found that DIXDC1 knockdown decreased the expression of β-catenin and restricted the activation of Wnt signaling. In addition, DIXDC1 knockdown decreased the expression of Wnt/β-catenin target genes, including cyclin D1 and c-myc, while DIXDC1 overexpression had the opposite effect. Notably, β-catenin knockdown partially reversed the oncogenic effect of DIXDC1 in AML cells. Taken together, these results demonstrate that DIXDC1 promotes the growth of AML cells, possibly through upregulating the Wnt/β-catenin signaling pathway. Our study suggests that DIXDC1 may serve as a potential therapeutic target for the treatment of AML.

Inhibition of DIXDC1 by microRNA-1271 suppresses the proliferation and invasion of prostate cancer cells

Disheveled-Axin domain containing 1 (DIXDC1) is involved in the development and progression of multiple cancers. However, the function significance of DIXDC1 in prostate cancer remains unclear. In this study, we investigated the function of DIXDC1 in prostate cancer and the regulation of DIXDC1 by microRNAs (miRNAs). We found that DIXDC1 was highly expressed in prostate cancer cells. Knockdown of DIXDC1 by small interfering RNAs markedly suppressed proliferation, invasion and Wnt signaling in prostate cancer cells. DIXDC1 was identified as a target gene of miR-1271 by bioinformatics analysis, dual-luciferase reporter assay, real-time quantitative polymerase chain reaction and Western blot analysis. Furthermore, DIXDC1 expression was inversely correlated with miR-1271 expression in prostate cancer tissues. The overexpression of miR-1271 significantly inhibited proliferation, invasion and Wnt signaling in prostate cancer cells. However, the inhibition of miR-1271 exhibits the opposite effects. Moreover, the overexpression of DIXDC1 significantly reversed the inhibitory effects of miR-1271 overexpression. Taken together, our results suggest that DIXDC1 plays an important role in regulating prostate cancer cell proliferation and invasion. Targeting DIXDC1 by miR-1271 may be a promising therapeutic strategy for prostate cancer.

Expression of Dixdc1 and its Role in Astrocyte Proliferation after Traumatic Brain Injury

DIX domain containing 1 (Dixdc1), a positive regulator of Wnt signaling pathway, is recently reported to play a role in the neurogenesis. However, the distribution and function of Dixdc1 in the central nervous system (CNS) after brain injury are still unclear. We used an acute traumatic brain injury (TBI) model in adult rats to investigate whether Dixdc1 is involved in CNS injury and repair. Western blot analysis and immunohistochemistry showed a time-dependent up-regulation of Dixdc1 expression in ipsilateral cortex after TBI. Double immunofluorescent staining indicated a colocalization of Dixdc1 with astrocytes and neurons. Moreover, we detected a colocalization of Ki-67, a cell proliferation marker with GFAP and Dixdc1 after TBI. In primary cultured astrocytes stimulated with lipopolysaccharide, we found enhanced expression of Dixdc1 in parallel with up-regulation of Ki-67 and cyclin A, another cell proliferation marker. In addition, knockdown of Dixdc1 expression in primary astrocytes with Dixdc1-specific siRNA transfection induced G0/G1 arrest of cell cycle and significantly decreased cell proliferation. In conclusion, all these data suggest that up-regulation of Dixdc1 protein expression is potentially involved in astrocyte proliferation after traumatic brain injury in the rat.

Knockdown of DIXDC1 Inhibits the Proliferation and Migration of Human Glioma Cells

DIX domain containing 1 (DIXDC1), the human homolog of coiled-coil-DIX1 (Ccd1), is a positive regulator of Wnt signaling pathway. Recently, it was found to act as a candidate oncogene in colon cancer, non-small-cell lung cancer, and gastric cancer. In this study, we aimed to investigate the clinical significance of DIXDC1 expression in human glioma and its biological function in glioma cells. Western blot and immunohistochemistry analysis showed that DIXDC1 was overexpressed in glioma tissues and glioma cell lines. The expression level of DIXDC1 was evidently linked to glioma pathological grade and Ki-67 expression. Kaplan-Meier curve showed that high expression of DIXDC1 may lead to poor outcome of glioma patients. Serum starvation and refeeding assay indicated that the expression of DIXDC1 was associated with cell cycle. To determine whether DIXDC1 could regulate the proliferation and migration of glioma cells, we transfected glioma cells with interfering RNA-targeting DIXDC1; investigated cell proliferation with Cell Counting Kit (CCK)-8, flow cytometry assays, and colony formation analyses; and investigated cell migration with wound healing assays and transwell assays. According to our data, knockdown of DIXDC1 significantly inhibited proliferation and migration of glioma cells. These data implied that DIXDC1 might participate in the development of glioma, suggesting that DIXDC1 can become a potential therapeutic strategy for glioma.

DIXDC1 activates the Wnt signaling pathway and promotes gastric cancer cell invasion and metastasis

DIXDC1 (Dishevelled-Axin domain containing 1) is a DIX (Dishevelled-Axin) domain-possessing protein that promotes colon cancer cell proliferation and increases the invasion and migration ability of non-small-cell lung cancer via the PI3K pathway. As a positive regulator of the Wnt/β-catenin pathway, the biological role of DIXDC1 in human gastric cancer and the relationship between DIXDC1 and the Wnt pathway are unclear. In the current study, the upregulation of DIXDC1 was detected in gastric cancer and was associated with advanced TNM stage cancer, lymph node metastasis, and poor prognosis. We also found that the overexpression of DIXDC1 could promote the invasion and migration of gastric cancer cells. The upregulation of MMPs and the downregulation of E-cadherin were found to be involved in the process. DIXDC1 enhanced β-catenin nuclear accumulation, which activated the Wnt pathway. Additionally, the inhibition of β-catenin in DIXDC1-overexpressing cells reversed the metastasis promotion effects of DIXDC1. These results demonstrate that the expression of DIXDC1 is associated with poor prognosis of gastric cancer patients and that DIXDC1 promotes gastric cancer invasion and metastasis through the activation of the Wnt pathway; E-cadherin and MMPs are also involved in this process. © 2015 Wiley Periodicals, Inc.

Csn3 gene is regulated by all-trans retinoic acid during neural differentiation in mouse P19 cells

κ-Casein (CSN3) is known to play an essential role in controlling the stability of the milk micelles. We found that the expression of Csn3 was induced by all-trans retinoic acid (ATRA) during neural differentiation in P19 embryonal carcinoma cells from our study using DNA microarray. In this paper, we describe the detailed time course of Csn3 expression and the induction mechanism of Csn3 transcription activation in this process. The Csn3 expression was induced rapidly and transiently within 24 h of ATRA treatment. Retinoic acid receptor (RAR)-specific agonists were used in expression analysis to identify the RAR subtype involved upregulation of Csn3; a RARα-specific agonist mimicked the effects of ATRA on induction of Csn3 expression. Therefore, RARα may be the RAR subtype mediating the effects of ATRA on the induction of Csn3 gene transcription in this differentiation-promoting process of P19 cells. We found that the promoter region of Csn3 contained a typical consensus retinoic acid response element (RARE), and this RARE was necessary for ATRA-dependent transcriptional regulation. We confirmed that RARα bound to this RARE sequence in P19 cells. These findings indicated that the Csn3 expression is upregulated via ATRA-bound RARα and binding of this receptor to the RARE in the Csn3 promoter region. This will certainly serve as a first step forward unraveling the mysteries of induction of Csn3 in the process of neural differentiation.

Tracing synaptic connectivity onto embryonic stem cell-derived neurons

Transsynaptic circuit tracing using genetically modified rabies virus (RV) is an emerging technology for identifying synaptic connections between neurons. Complementing this methodology, it is now possible to assay the basic molecular and cellular properties of neuronal lineages derived from embryonic stem cells (ESCs) in vitro, and these properties are under intense investigation toward devising cell replacement therapies. Here, we report the generation of a novel mouse ESC (mESC) line that harbors the genetic elements to allow RV-mediated transsynaptic circuit tracing in ESC-derived neurons and their synaptic networks. To facilitate transsynaptic tracing, we have engineered a new reporter allele by introducing cDNA encoding tdTomato, the Rabies-G glycoprotein, and the avian TVA receptor into the ROSA26 locus by gene targeting. We demonstrate high-efficiency differentiation of these novel mESCs into functional neurons, show their capacity to synaptically connect with primary neuronal cultures as evidenced by immunohistochemistry and electrophysiological recordings, and show their ability to act as source cells for presynaptic tracing of neuronal networks in vitro and in vivo. Together, our data highlight the potential for using genetically engineered stem cells to investigate fundamental mechanisms of synapse and circuit formation with unambiguous identification of presynaptic inputs onto neuronal populations of interest.

Crystallographic characterization of the DIX domain of the Wnt signalling positive regulator Ccd1

Coiled-coil DIX1 (Ccd1) is a positive regulator that activates the canonical Wnt signalling pathway by inhibiting the degradation of the key signal transducer β-catenin. The C-terminal DIX domain of Ccd1 plays an important role in the regulation of signal transduction through homo-oligomerization and protein complex formation with other DIX domain-containing proteins, i.e. axin and dishevelled proteins. Here, the expression, purification, crystallization and X-ray data collection of the Ccd1 DIX domain are reported. The crystals of the Ccd1 DIX domain belonged to space group P2(1)2(1)2(1), with unit-cell parameters a=72.9, b=75.7, c=125.6 Å. An X-ray diffraction data set was collected at 3.0 Å resolution.

Bis is involved in glial differentiation of p19 cells induced by retinoic Acid

Previous observations suggest that Bis, a Bcl-2-binding protein, may play a role the neuronal and glial differentiation in vivo. To examine this further, we investigated Bis expression during the in vitro differentiation of P19 embryonic carcinoma cells induced by retinoic acid (RA). Western blotting and RT-PCR assays showed that Bis expression was temporarily decreased during the free floating stage and then began to increase on day 6 after the induction of differentiation. Double immunostaining indicated that Bis-expressing cells do not express several markers of differentiation, including NeuN, MAP-2 and Tuj-1. However, some of the Bis-expressing cells also were stained with GFAP-antibodies, indicating that Bis is involved glial differentiation. Using an shRNA strategy, we developed bis-knock down P19 cells and compared them with control P19 cells for the expression of NeuroD, Mash-1 and GFAP during RA-induced differentiation. Among these, only GFAP induction was significantly attenuated in P19-dnbis cells and the population showing GFAP immunoreactivity was also decreased. It is noteworthy that distribution of mature neurons and migrating neurons was disorganized, and the close association of migrating neuroblasts with astrocytes was not observed in P19-dnbis cells. These results suggest that Bis is involved in the migration-inducing activity of glial cells.

DIXDC1 co-localizes and interacts with gamma-tubulin in HEK293 cells

DIXDC1 is a Dishevelled-Axin (DIX) domain-containing protein involved in neural development and Wnt signaling pathway. Besides the DIX domain, DIXDC1 also contains a coiled-coil domain (MTH domain), which is a common feature of centrosomal proteins. We have demonstrated that exogenously expressed GFP-tag fused DIXDC1 co-localize with gamma-tubulin both at interphase and mitotic phase in HEK293 cells. By immunostaining with anti-DIXDC1 and anti-gamma-tubulin antibody, endogenous DIXDC1 was also co-localized with gamma-tubulin at the centrosomes in HEK293 cells. We confirmed this interaction of DIXDC1 with gamma-tubulin by co-immunoprecipitation. The findings suggest that DIXDC1 might play an important role in chromosome segregation and cell cycle regulation.