The conserved WRPW motif of Hes6 mediates proteasomal degradation

Activation of Hes1 and Msx1 in Transgenic Mouse Embryonic Stem Cells Increases Differentiation into Neural Crest Derivatives

The neural crest (NC) comprises a multipotent cell population that produces peripheral neurons, cartilage, and smooth muscle cells, among other phenotypes. The participation of Hes1 and Msx1 when expressed in mouse embryonic stem cells (mESCs) undergoing NC differentiation is unexplored. In this work, we generated stable mESCs transfected with constructs encoding chimeric proteins in which the ligand binding domain of glucocorticoid receptor (GR), which is translocated to the nucleus by dexamethasone addition, is fused to either Hes1 (HGR) or Msx1 (MGR), as well as double-transgenic cells (HGR+MGR). These lines continued to express pluripotency markers. Upon NC differentiation, all lines exhibited significantly decreased Sox2 expression and upregulated Sox9, Snai1, and Msx1 expression, indicating NC commitment. Dexamethasone was added to induce nuclear translocation of the chimeric proteins. We found that Collagen IIa transcripts were increased in MGR cells, whereas coactivation of HGR+MGR caused a significant increase in Smooth muscle actin (α-Sma) transcripts. Immunostaining showed that activation in HGR+MGR cells induced higher proportions of β-TUBULIN III⁺, α-SMA⁺ and COL2A1⁺ cells. These findings indicate that nuclear translocation of MSX-1, alone or in combination with HES-1, produce chondrocyte-like cells, and simultaneous activation of HES-1 and MSX-1 increases the generation of smooth muscle and neuronal cells.

The oncogenic effects of HES1 on salivary adenoid cystic carcinoma cell growth and metastasis

Background

Our previous study demonstrated a close relationship between NOTCH signaling pathway and salivary adenoid cystic carcinoma (SACC). HES1 is a well-known target gene of NOTCH signaling pathway. The purpose of the present study was to further explore the molecular mechanism of HES1 in SACC.

Methods

Comparative transcriptome analyses by RNA-Sequencing (RNA-Seq) were employed to reveal NOTCH1 downstream gene in SACC cells. Immunohistochemical staining was used to detect the expression of HES1 in clinical samples. After HES1-siRNA transfected into SACC LM cells, the cell proliferation and cell apoptosis were tested by suitable methods; animal model was established to detect the change of growth ability of tumor. Transwell and wound healing assays were used to evaluate cell metastasis and invasion.

Results

We found that HES1 was strongly linked to NOTCH signaling pathway in SACC cells. The immunohistochemical results implied the high expression of HES1 in cancerous tissues. The growth of SACC LM cells transfected with HES1-siRNAs was significantly suppressed in vitro and tumorigenicity in vivo by inducing cell apoptosis. After HES1 expression was silenced, the SACC LM cell metastasis and invasion ability was suppressed.

Conclusions

The results of this study demonstrate that HES1 is a specific downstream gene of NOTCH1 and that it contributes to SACC proliferation, apoptosis and metastasis. Our findings serve as evidence indicating that HES1 may be useful as a clinical target in the treatment of SACC.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4350-5) contains supplementary material, which is available to authorized users.

The E3 ubiquitin ligase SCFFBXL14 complex stimulates neuronal differentiation by targeting the Notch signaling factor HES1 for proteolysis

Molecular oscillators are important cellular regulators of, for example, circadian clocks, oscillations of immune regulators, and short-period (ultradian) rhythms during embryonic development. The Notch signaling factor HES1 (hairy and enhancer of split 1) is a well-known repressor of proneural genes, and HES1 ultradian oscillation is essential for keeping cells in an efficiently proliferating progenitor state. HES1 oscillation is driven by both transcriptional self-repression and ubiquitin-dependent proteolysis. However, the E3 ubiquitin ligase targeting HES1 for proteolysis remains unclear. Based on siRNA-mediated gene silencing screening, co-immunoprecipitation, and ubiquitination assays, we discovered that the E3 ubiquitin ligase SCF^FBXL14 complex regulates HES1 ubiquitination and proteolysis. siRNA-mediated knockdown of the Cullin-RING E3 ubiquitin ligases RBX1 or CUL1 increased HES1 protein levels, prolonged its half-life, and dampened its oscillation. FBXL14, an F-box protein for SCF ubiquitin ligase, associates with HES1. FBXL14 silencing stabilized HES1, whereas FBXL14 overexpression decreased HES1 protein levels. Of note, the SCF^FBXL14 complex promoted the ubiquitination of HES1 in vivo, and a conserved WRPW motif in HES1 was essential for HES1 binding to FBXL14 and for ubiquitin-dependent HES1 degradation. HES1 knockdown promoted neuronal differentiation, but FBXL14 silencing inhibited neuronal differentiation induced by HES1 ablation in mES and F9 cells. Our results suggest that SCF^FBXL14 promotes neuronal differentiation by targeting HES1 for ubiquitin-dependent proteolysis and that the C-terminal WRPW motif in HES1 is required for this process.

Basic helix-loop-helix transcription factors in evolution: Roles in development of mesoderm and neural tissues

Basic helix-loop-helix (bHLH) transcription factors have attracted the attention of developmental and evolutionary biologists for decades because of their conserved functions in mesodermal and neural tissue formation in both vertebrates and fruit flies. Their evolutionary history is of special interest because it will likely provide insights into developmental processes and refinement of metazoan-specific traits. This review briefly considers advances in developmental biological studies on bHLHs/HLHs. I also discuss recent genome-wide surveys and molecular phylogenetic analyses of these factors in a wide range of metazoans. I hypothesize that interactions between metazoan-specific Group A, D, and E bHLH/HLH factors enabled a sophisticated transition system from cell proliferation to differentiation in multicellular development. This control mechanism probably emerged initially to organize a multicellular animal body and was subsequently recruited to form evolutionarily novel tissues, which differentiated during a later ontogenetic phase.

Sumoylation of Hes6 Regulates Protein Degradation and Hes1-Mediated Transcription

BACKGROUND

Hes6 is a transcriptional regulator that induces transcriptional activation by binding to transcription repressor Hes1 and suppressing its activity. Hes6 is controlled by the ubiquitin-proteosome-mediated degradation system. Here we investigated the sumoylation of Hes6 and its functional role in its rhythmic expression.

METHODS

Hes6, SUMO, and ubiquitin were transfected into HeLa cells and the expression pattern was observed by Western blot and immunoprecipitation. To confirm the effect of sumoylation on the rhythmic expression of Hes6, we generated mouse Hes6 promoter-driven GFP-Hes6 fusion constructs and expressed these constructs in NIH 3T3 cells.

RESULTS

Overexpression of SUMO led to sumoylation of Hes6 at both lysine 27 and 30. Protein stability of Hes6 was decreased by sumoylation. Moreover, expression of a Hes6 sumoylation-defective mutant, the 2KR (K27/30R) mutant, or co-expression of SUMO protease SUSP1 with native Hes6, strongly reduced ubiquitination. In addition, sumoylation was associated with both the rhythmic expression and transcriptional regulation of Hes6. Wild type Hes6 showed oscillatory expression with about 2-hour periodicity, whereas the 2KR mutant displayed a longer period. Furthermore, sumoylation of Hes6 derepressed Hes1-induced transcriptional repression.

CONCLUSION

Hes6 sumoylation plays an important role in the regulation of its stability and Hes1-mediated transcription. These results suggest that sumoylation may be crucial for rhythmic expression of Hes6 and downstream target genes.

bHLH proteins involved in Drosophila neurogenesis are mutually regulated at the level of stability

Proneural bHLH activators are expressed in all neuroectodermal regions prefiguring events of central and peripheral neurogenesis. Drosophila Sc is a prototypical proneural activator that heterodimerizes with the E-protein Daughterless (Da) and is antagonized by, among others, the E(spl) repressors. We determined parameters that regulate Sc stability in Drosophila S2 cells. We found that Sc is a very labile phosphoprotein and its turnover takes place via at least three proteasome-dependent mechanisms. (i) When Sc is in excess of Da, its degradation is promoted via its transactivation domain (TAD). (ii) In a DNA-bound Da/Sc heterodimer, Sc degradation is promoted via an SPTSS phosphorylation motif and the AD1 TAD of Da; Da is spared in the process. (iii) When E(spl)m7 is expressed, it complexes with Sc or Da/Sc and promotes their degradation in a manner that requires the corepressor Groucho and the Sc SPTSS motif. Da/Sc reciprocally promotes E(spl)m7 degradation. Since E(spl)m7 is a direct target of Notch, the mutual destabilization of Sc and E(spl) may contribute in part to the highly conserved anti-neural activity of Notch. Sc variants lacking the SPTSS motif are dramatically stabilized and are hyperactive in transgenic flies. Our results propose a novel mechanism of regulation of neurogenesis, involving the stability of key players in the process.

Differential regulation of Hes/Hey genes during inner ear development

Notch signaling plays a crucial role during inner ear development and regeneration. Hes/Hey genes encode for bHLH transcription factors identified as Notch targets. We have studied the expression and regulation of Hes/Hey genes during inner ear development in the chicken embryo. Among several Hes/Hey genes examined, only Hey1 and Hes5 map to the sensory regions, although with salient differences. Hey1 expression follows Jag1 expression except at early prosensory stages while Hes5 expression corresponds well to Dl1 expression throughout otic development. Although Hey1 and Hes5 are direct Notch downstream targets, they differ in the level of Notch required for activation. Moreover, they also differ in mRNA stability, showing different temporal decays after Notch blockade. In addition, Bmp, Wnt and Fgf pathways also modify Hey1 and Hes5 expression in the inner ear. Particularly, the Wnt pathway modulates Hey1 and Jag1 expression. Finally, gain of function experiments show that Hey1 and Hes5 cross-regulate each other in a complex manner. Both Hey1 and Hes5 repress Dl1 and Hes5 expression, suggesting that they prevent the transition to differentiation stages, probably by preventing Atoh1 expression. In spite of its association with Jag1, Hey1 does not seem to be instrumental for lateral induction as it does not promote Jag1 expression. We suggest that, besides being both targets of Notch, Hey1 and Hes5 are subject to a rather complex regulation that includes the stability of their transcripts, cross regulation and other signaling pathways.

HES6 enhances the motility of alveolar rhabdomyosarcoma cells

HES6, a member of the hairy-enhancer-of-split family of transcription factors, plays multiple roles in myogenesis. It is a direct target of the myogenic transcription factor MyoD and has been shown to regulate the formation of the myotome in development, myoblast cell cycle exit and the organization of the actin cytoskeleton during terminal differentiation. Here we investigate the expression and function of HES6 in rhabdomyosarcoma, a soft tissue tumor which expresses myogenic genes but fails to differentiate into muscle. We show that HES6 is expressed at high levels in the subset of alveolar rhabdomyosarcomas expressing PAX/FOXO1 fusion genes (ARMSp). Knockdown of HES6 mRNA in the ARMSp cell line RH30 reduces proliferation and cell motility. This phenotype is rescued by expression of mouse Hes6 which is insensitive to HES6 siRNA. Furthermore, expression microarray analysis indicates that the HES6 knockdown is associated with a decrease in the levels of Transgelin, (TAGLN), a regulator of the actin cytoskeleton. Knockdown of TAGLN decreases cell motility, whilst TAGLN overexpression rescues the motility defect resulting from HES6 knockdown. These findings indicate HES6 contributes to the pathogenesis of ARMSp by enhancing both proliferation and cell motility.

FGF/MAPK/Ets signaling renders pigment cell precursors competent to respond to Wnt signal by directly controlling Ci-Tcf transcription

FGF and Wnt pathways constitute two fundamental signaling cascades, which appear to crosstalk in cooperative or antagonistic fashions in several developmental processes. In vertebrates, both cascades are involved in pigment cell development, but the possible interplay between FGF and Wnt remains to be elucidated. In this study, we have investigated the role of FGF and Wnt signaling in development of the pigment cells in the sensory organs of C. intestinalis. This species possesses the basic features of an ancestral chordate, thus sharing conserved molecular developmental mechanisms with vertebrates. Chemical and targeted perturbation approaches revealed that a FGF signal, spreading in time from early gastrulation to neural tube closure, is responsible for pigment cell precursor induction. This signal is transmitted via the MAPK pathway, which activates the Ci-Ets1/2 transcription factor. Targeted perturbation of Ci-TCF, a downstream factor of the canonical Wnt pathway, indicated its contribution to pigment cell differentiation Furthermore, analyses of the Ci-Tcf regulatory region revealed the involvement of the FGF effector, Ci-Ets1/2, in Ci-Tcf transcriptional regulation in pigment cell precursors. Our results indicate that both FGF and the canonical Wnt pathways are involved in C. intestinalis pigment cell induction and differentiation. Moreover, we present a case of direct transcriptional regulation exerted by the FGF signaling cascade, via the MAPK-ERK-Ets1/2, on the Wnt downstream gene Ci-Tcf. Several examples of FGF/Wnt signaling crosstalk have been described in different developmental processes; however, to our knowledge, FGF-Wnt cross-interaction at the transcriptional level has never been previously reported. These findings further contribute to clarifying the multitude of FGF-Wnt pathway interactions.

Ultradian oscillations in Notch signaling regulate dynamic biological events

Notch signaling regulates many dynamic processes; accordingly, expression of genes in this pathway is also dynamic. In mouse embryos, one dynamic process regulated by Notch is somite segmentation, which occurs with a 2-h periodicity. This periodic event is regulated by a biological clock called the segmentation clock, which involves cyclic expression of the Notch effector gene Hes7. Loss of Hes7 expression and sustained expression of Hes7 result in identical and severe somite defects, suggesting that Hes7 oscillation is required for proper somite segmentation. Mathematical models of this oscillator have been used to generate and test hypothesis, helping to uncover the role of negative feedback in regulating the oscillator. Oscillations of another Notch effector gene, Hes1, plays an important role in maintenance of neural stem cells. Hes1 expression oscillates with a period of about 2-3h in neural stem cells, whereas sustained Hes1 expression inhibits proliferation and differentiation of these cells, suggesting that Hes1 oscillations are important for their proper activities. Hes1 inhibits its own expression as well as the expression of the proneural gene Neurogenin2 and the Notch ligand Delta1, driving oscillations of these two genes. Delta1 oscillations in turn maintain neural stem cells by mutual activation of Notch signaling, which re-activates Hes1 to close the cycle. Hes1 expression also oscillates in embryonic stem (ES) cells. Cells expressing low and high levels of Hes1 tend to differentiate into neural and mesodermal cells, respectively. Furthermore, Hes1-null ES cells display early and uniform neural differentiation, indicating that Hes1 oscillations act to promote multipotency by generating heterogeneity in both the differentiation timing and the fate choice. Taken together, these results suggest that Notch signaling can drive short-period oscillatory expression of Hes7 and Hes1 (ultradian oscillation) and that ultradian oscillations are important for many biological events.

HES1 regulates 5-HT1A receptor gene transcription at a functional polymorphism: essential role in developmental expression

Mammalian HES1 and HES5 are abundant in developing CNS and inhibit neurogenesis, while HES6 promotes neurogenesis. An early serotonergic differentiation marker, the 5-HT1A receptor, is repressed by HES5 and DEAF1 which recognize the C(-1019), but not G(-1019) allele of a human 5-HT1A promoter polymorphism associated with mood disorders. We tested whether HES1 and HES6 regulate transcriptional activity at this element. HES1 strongly repressed 5-HT1A transcription in neuronal and non-neuronal cells, while HES6 reversed HES1- and HES5-mediated repression. Mutation of a putative HES consensus site blocked HES1 and HES5, but, unlike HES5, HES1 repressed at the G(-1019) allele. To address its role in vivo, the temporal expression of 5-HT1A receptor RNA and protein was examined in HES1-/- mice, and elevated levels in E12.5 hindbrain and midbrain were observed. Thus, HES1 and HES6 oppositely regulate 5-HT1A receptor transcription and HES1 is required for its correct developmental expression.

Hes6 controls cell proliferation via interaction with cAMP-response element-binding protein-binding protein in the promyelocytic leukemia nuclear body

Hes6 is a basic helix-loop-helix transcription factor that functions in the differentiation of pluripotent progenitor cells and during tumorigenesis. However, the molecular mechanism for its function is largely unknown. Here we show that Hes6 is a component of the promyelocytic leukemia nuclear body (PML-NB) complex in the nuclei and that Hes6 inhibits cell proliferation through induction of p21 cyclin-dependent kinase inhibitor. We further show that Hes6 directly interacts with CREB-binding protein (CBP), one of the key components of PML-NB, via its basic domain. This association is critical for p21 induction through multiple mechanisms, including chromatin remodeling and p53 acetylation. Taken together, these results suggest that the Hes6-CBP complex in PML-NB may influence the proliferation of cells via p53-dependent and -independent pathways.

Hes6 is required for MyoD induction during gastrulation

The specification of mesoderm into distinct compartments sharing the same lineage restricted fates is a crucial step occurring during gastrulation, and is regulated by morphogenic signals such as the FGF/MAPK and activin pathways. One target of these pathways is the transcription factor XmyoD, which in early gastrulation is expressed in the lateral and ventral mesoderm. Expression of the hairy/enhancer of split transcription factor hes6, is also restricted to lateral and ventral mesoderm in gastrula stage Xenopus embryos, leading us to investigate whether it has a role in XmyoD regulation. In vivo, Xhes6 is required for FGF-mediated induction of XmyoD expression but not for induction of early mesoderm. The WRPW domain of Xhes6, which binds Groucho family transcriptional co-regulators, is essential for the XmyoD-inducing activity of Xhes6. Two Groucho proteins, Xgrg2 and Xgrg4, are expressed in lateral and ventral mesoderm, and inhibit expression of XmyoD. Xhes6 binds both Xgrg2 and Xgrg4 and relieves their inhibition of XmyoD expression. We also find that lowering Xhes6 expression levels blocks normal myogenic differentiation at tail bud stage. We conclude that Xhes6 is essential for XmyoD induction and acts by relieving Groucho-mediated repression of gene expression.

Inhibition of cortical astrocyte differentiation by Hes6 requires amino- and carboxy-terminal motifs important for dimerization and phosphorylation

Hairy/Enhancer of split (Hes) 6 is a basic helix-loop-helix protein that interacts with the transcriptional co-repressor, Groucho, and antagonizes the neural functions of the Notch pathway. More specifically, mouse Hes6 regulates cerebral corticogenesis by promoting neurogenesis and suppressing astrocyte differentiation. The molecular mechanisms underlying the anti-astrogenic function of Hes6 are poorly defined. Here we describe studies aimed at testing whether Hes6 inhibits astrocyte differentiation by antagonizing the transcription repression activity of Notch-activated Hes family members like Hes1. It is reported that Hes6 preferentially forms homodimers. Heterodimerization with Hes1 is antagonized in part by a conserved N-terminal patch of negatively charged residues. Mutation of this motif enhances heterodimerization with Hes1 and increases Hes6 ability to antagonize Hes1-mediated transcriptional repression. However, this mutation does not increase, but instead decreases, the anti-astrogenic activity of Hes6. It is shown further that Hes6 harbors a second conserved sequence, a C-terminal SPXXSP motif. This sequence is phosphorylated by the mitogen activated protein kinase pathway and its mutation disrupts the anti-astrogenic activity of Hes6 without affecting its ability to suppress Hes1. Together, these observations suggest that Hes6 homodimers regulate astrocyte differentiation through mechanisms that depend on the phosphorylation of Hes6 C-terminal domain but are independent of its ability to suppress Hes1-mediated transcriptional repression.

The Hes gene family: repressors and oscillators that orchestrate embryogenesis

Embryogenesis involves orchestrated processes of cell proliferation and differentiation. The mammalian Hes basic helix-loop-helix repressor genes play central roles in these processes by maintaining progenitor cells in an undifferentiated state and by regulating binary cell fate decisions. Hes genes also display an oscillatory expression pattern and control the timing of biological events, such as somite segmentation. Many aspects of Hes expression are regulated by Notch signaling, which mediates cell-cell communication. This primer describes these pleiotropic roles of Hes genes in some developmental processes and aims to clarify the basic mechanism of how gene networks operate in vertebrate embryogenesis.

The molecular basis of neurosensory cell formation in ear development: a blueprint for hair cell and sensory neuron regeneration?

The inner ear of mammals uses neurosensory cells derived from the embryonic ear for mechanoelectric transduction of vestibular and auditory stimuli (the hair cells) and conducts this information to the brain via sensory neurons. As with most other neurons of mammals, lost hair cells and sensory neurons are not spontaneously replaced and result instead in age-dependent progressive hearing loss. We review the molecular basis of neurosensory development in the mouse ear to provide a blueprint for possible enhancement of therapeutically useful transformation of stem cells into lost neurosensory cells. We identify several readily available adult sources of stem cells that express, like the ectoderm-derived ear, genes known to be essential for ear development. Use of these stem cells combined with molecular insights into neurosensory cell specification and proliferation regulation of the ear, might allow for neurosensory regeneration of mammalian ears in the near future.

Hes6 inhibits astrocyte differentiation and promotes neurogenesis through different mechanisms

The mechanisms regulating the generation of cell diversity in the mammalian cerebral cortex are beginning to be elucidated. In that regard, Hairy/Enhancer of split (Hes) 1 and 5 are basic helix-loop-helix (bHLH) factors that inhibit the differentiation of pluripotent cortical progenitors into neurons. In contrast, a related Hes family member termed Hes6 promotes neurogenesis. It is shown here that knockdown of endogenous Hes6 causes supernumerary cortical progenitors to differentiate into cells that exhibit an astrocytic morphology and express the astrocyte marker protein GFAP. Conversely, exogenous Hes6 expression in cortical progenitors inhibits astrocyte differentiation. The negative effect of Hes6 on astrocyte differentiation is independent of its ability to promote neuronal differentiation. We also show that neither its proneuronal nor its anti-gliogenic functions appear to depend on Hes6 ability to bind to DNA via the basic arm of its bHLH domain. Both of these activities require Hes6 to be localized to nuclei, but only its anti-gliogenic function depends on two short peptides, LNHLL and WRPW, that are conserved in all Hes6 proteins. These findings suggest that Hes6 is an important regulator of the neurogenic phase of cortical development by promoting the neuronal fate while suppressing astrocyte differentiation. They suggest further that separate molecular mechanisms underlie the proneuronal and anti-gliogenic activities of Hes6 in cortical progenitor cells.