The C-terminal cytoplasmic tail of hedgehog receptor Patched1 is a platform for E3 ubiquitin ligase complexes

Splice variants of CK1α and CK1α-like: Comparative analysis of subcellular localization, kinase activity, and function in the Wnt signaling pathway

Members of the casein kinase 1 (CK1) family are important regulators of multiple signaling pathways. CK1α is a well-known negative regulator of the Wnt/β-catenin pathway, which promotes the degradation of β-catenin via its phosphorylation of Ser45. In contrast, the closest paralog of CK1α, CK1α-like, is a poorly characterized kinase of unknown function. In this study, we show that the deletion of CK1α, but not CK1α-like, resulted in a strong activation of the Wnt/β-catenin pathway. Wnt-3a treatment further enhanced the activation, which suggests there are at least two modes, a CK1α-dependent and Wnt-dependent, of β-catenin regulation. Rescue experiments showed that only two out of ten naturally occurring splice CK1α/α-like variants were able to rescue the augmented Wnt/β-catenin signaling caused by CK1α deficiency in cells. Importantly, the ability to phosphorylate β-catenin on Ser45 in the in vitro kinase assay was required but not sufficient for such rescue. Our compound CK1α and GSK3α/β KO models suggest that the additional nonredundant function of CK1α in the Wnt pathway beyond Ser45-β-catenin phosphorylation includes Axin phosphorylation. Finally, we established NanoBRET assays for the three most common CK1α splice variants as well as CK1α-like. Target engagement data revealed comparable potency of known CK1α inhibitors for all CK1α variants but not for CK1α-like. In summary, our work brings important novel insights into the biology of CK1α, including evidence for the lack of redundancy with other CK1 kinases in the negative regulation of the Wnt/β-catenin pathway at the level of β-catenin and Axin.

LncRNA LINC01871 sponging miR-142-3p to modulate ZYG11B promotes the chemoresistance of colorectal cancer cells by inducing autophagy

BACKGROUND

Colorectal cancer (CRC) is a malignant tumor in the digestive tract. Increasing evidence indicated that chemoresistance leads to a poor prognosis of CRC. Herein, we aimed to uncover the potential mechanism by which long intergenic noncoding RNA-1871 (LINC01871) affects the chemoresistance of CRC cells.

METHODS

Relative level of LINC01871 in CRC tissues was assessed by reverse transcription quantitative PCR (RT-qPCR). Kaplan-Meier analysis was conducted to determine the relevance of LINC01871 and the prognosis of CRC patients. Cell Counting Kit-8 (CCK-8) and colony formation assay were used to evaluate the proliferation of SW480 cells. Expression levels of proteins and their genes were assessed by western blot, immunofluorescence staining and RT-qPCR. In addition, the interaction of LINC01871, miR-142-3p and protein zyg-11 homolog B (ZYG11B) were analyzed via dual-luciferase reporter assays.

RESULTS

LINC01871 was low-expressed in CRC tissues and cell lines. Patients with a low level of LINC01871 showed significantly lower survival rate. pcDNA-LINC01871 significantly reduced the viability of SW480 cells ( P  < 0.01), elevated SW480 cells sensitivity to 5-FU ( P  < 0.01), reduced LC3 punctate aggregates ( P  < 0.01) and downregulated the relative mRNA expression level of autophagy related protein 9A, autophagy related protein 4B and high mobility group box 1 ( P  < 0.01) in SW480 cells. Moreover, LINC01871 was found to sponge miR-142-3p, and ZYG11B was the target of miR-142-3p. MiR-142-3p mimic significantly recovered the effect of pcDNA-LINC001871, whereas pcDNA-ZYG11B reversed the recovery effect of the miR-142-3p mimic.

CONCLUSION

LINC01871/miR-142-3p/ ZYG11B axis regulates the chemoresistance of CRCs by inducing autophagy.

NF-κB-activated SPRY4-IT1 promotes cancer cell metastasis by downregulating TCEB1 mRNA via Staufen1-mediated mRNA decay

Previous study demonstrated that most long non-coding RNAs (lncRNAs) function as competing endogenous RNAs or molecular sponges to negatively modulate miRNA and regulate tumor development. However, the molecular mechanisms of lncRNAs in cancer are not fully understood. Our study describes the role of the lncRNA SPRY4 intronic transcript 1 (SPRY4-IT1) in cancer metastasis by mechanisms related to Staufen1 (STAU1)-mediated mRNA decay (SMD). Briefly, we found that, high SPRY4-IT1 expression was associated with aggressiveness and poor outcome in human colorectal, breast and ovarian cancer tissues. In addition, functional assays revealed that SPRY4-IT1 significantly promoted colorectal, breast and ovarian cancer metastasis in vitro and in vivo. Mechanistically, microarray analyses identified several differentially-expressed genes upon SPRY4-IT1 overexpression in HCT 116 colorectal cancer cells. Among them, the 3'-UTR of transcription elongation factor B subunit 1 (TCEB1) mRNA can base-pair with the Alu element in the 3'-UTR of SPRY4-IT1. Moreover, SPRY4-IT1 was found to bind STAU1, promote STAU1 recruitment to the 3'-UTR of TCEB1 mRNA, and affect TCEB1 mRNA stability and expression, resulting in hypoxia-inducible factor 1α (HIF-1α) upregulation, and thereby affecting cancer cell metastasis. In addition, STAU1 depletion abrogated TCEB1 SMD and alleviated the pro-metastatic effect of SPRY4-IT1 overexpression. Significantly, we revealed that SPRY4-IT1 is also transactivated by NF-κB/p65, which activates SPRY4-IT1 to inhibit TCEB1 expression, and subsequently upregulate HIF-1α. In conclusion, our results highlight a novel mechanism of cytoplasmic lncRNA SPRY4-IT1 in which SPRY4-IT1 affecting TCEB1 mRNA stability via STAU1-mediated degradation during cancer metastasis.

Ubiquitin links smoothened to intraflagellar transport to regulate Hedgehog signaling

In the absence of Hedgehog ligand, patched-1 (Ptch1) localizes to cilia and prevents ciliary accumulation and activation of smoothened (Smo). Upon ligand binding, Ptch1 is removed from cilia, and Smo is derepressed and accumulates in cilia where it activates signaling. The mechanisms regulating these dynamic movements are not well understood, but defects in intraflagellar transport components, including Ift27 and the BBSome, cause Smo to accumulate in cilia without pathway activation. We find that in the absence of ligand-induced pathway activation, Smo is ubiquitinated and removed from cilia, and this process is dependent on Ift27 and BBSome components. Activation of Hedgehog signaling decreases Smo ubiquitination and ciliary removal, resulting in its accumulation. Blocking ubiquitination of Smo by an E1 ligase inhibitor or by mutating two lysine residues in intracellular loop three causes Smo to aberrantly accumulate in cilia without pathway activation. These data provide a mechanism to control Smo's ciliary level during Hedgehog signaling by regulating the ubiquitination state of the receptor.

Functional and genetic analyses of ZYG11B provide evidences for its involvement in OAVS

BACKGROUND

The Oculo-Auriculo-Vertebral Spectrum (OAVS) or Goldenhar Syndrome is an embryonic developmental disorder characterized by hemifacial microsomia associated with auricular, ocular and vertebral malformations. The clinical heterogeneity of this spectrum and its incomplete penetrance limited the molecular diagnosis. In this study, we describe a novel causative gene, ZYG11B.

METHODS

A sporadic case of OAVS was analyzed by whole exome sequencing in trio strategy. The identified candidate gene, ZYG11B, was screened in 143 patients by next generation sequencing. Overexpression and immunofluorescence of wild-type and mutated ZYG11B forms were performed in Hela cells. Moreover, morpholinos were used for transient knockdown of its homologue in zebrafish embryo.

RESULTS

A nonsense de novo heterozygous variant in ZYG11B, (NM_024646, c.1609G>T, p.Glu537*) was identified in a single OAVS patient. This variant leads in vitro to a truncated protein whose subcellular localization is altered. Transient knockdown of the zebrafish homologue gene confirmed its role in craniofacial cartilages architecture and in notochord development. Moreover, ZYG11B expression regulates a cartilage master regulator, SOX6, and is regulated by Retinoic Acid, a known developmental toxic molecule leading to clinical features of OAVS.

CONCLUSION

Based on genetic, cellular and animal model data, we proposed ZYG11B as a novel rare causative gene for OAVS.

Regulation of Stem Cells by Cullin-RING Ligase

Stem cells can remain quiescent, self-renewal, and differentiate into many types of cells and even cancer stem cells. The coordination of these complex processes maintains the homeostasis of the organism. Ubiquitination is an important posttranslational modification process that regulates protein stability and activity. The ubiquitination levels of stem cell-associated proteins are closely related with stem cell characteristics. Cullin-RING Ligases (CRLs) are the largest family of E3 ubiquitin ligases, accounting for approximately 20% of proteins degraded by proteasome. In this review, we discuss the role of CRLs in stem cell homeostasis, self-renewal, and differentiation and expound their ubiquitination substrates. In addition, we also discuss the effect of CRLs on the formation of cancer stem cells that may provide promising therapy strategies for cancer.