FBXL12-Mediated Degradation of ALDH3 is Essential for Trophoblast Differentiation During Placental Development

Protein turnover downstream of the Nipbl/CRL4 axis contributes to abnormal development in zebrafish embryos

BACKGROUND

Mutations in cohesins cause cohesinopathies such as Cornelia de Lange Syndrome (CdLS) and Roberts Syndrome (RBS). Prior findings demonstrate that Esco2 (a cohesin activator) and Smc3 (a core cohesin subunit) regulate the CRL4 E3 ubiquitin ligase. SMC3 mutations, however, account for a small percentage of CdLS. Here, we test whether NIPBL, which when mutated is responsible for 65% of CdLS cases, also regulates CRL4.

RESULTS

We report that Nipbl knockdown in zebrafish embryos produces developmental abnormalities and reduces the transcription of ddb1, which encodes a key component of CRL4 E3 ligase. The severity of phenotypes in Nipbl knockdown embryos is partially rescued by exogenous ddb1 mRNA, demonstrating that CRL4 ligase function is downstream of Nipbl. These findings suggest that aberrant accumulation of CRL4 ligase substrates contributes to developmental abnormalities. To test this model, we identified candidate CRL4 substrates in zebrafish embryos by LC-MS. The results reveal that elevated expression of one of these candidates, pparαa, is sufficient to produce developmental defects in zebrafish embryos.

CONCLUSIONS

Nipbl impacts CRL4 ligase activity via regulation of ddb1 expression. We provide evidence that the aberrant accumulation of substrates is sufficient to produce developmental abnormalities consistent with those observed in RBS and CdLS models.

Disruption of the sorcin‒PAX5 protein‒protein interaction induces ferroptosis by promoting the FBXL12-mediated ubiquitination of ALDH1A1 in pancreatic cancer

BACKGROUND

Pancreatic cancer is one of the most malignant cancers, and limited therapeutic options are available. The induction of ferroptosis is considered to be a novel, promising strategy that has potential in cancer treatment, and ferroptosis inducers may be new options for eradicating malignant cancers that are resistant to traditional drugs. The exact mechanism underlying the function of sorcin in the initiation and progression of pancreatic cancer remains unclear.

METHODS

The expression of sorcin in cancer tissues was assessed by analyzing TCGA, GEO and immunohistochemical staining data, and the function of sorcin in the induction of ferroptosis in pancreatic cancer cells was investigated. The mechanism underlying the function of sorcin was revealed through proteomics, co-IP, Ch-IP, and luciferase assays. Natural product screening was subsequently performed to screen for products that interact with sorcin to identify new ferroptosis inducers.

RESULTS

We first showed that sorcin expression was positively correlated with the survival and tumor stages of patients with pancreatic cancer, and we revealed that sorcin inhibited ferroptosis through its noncalcium binding function. Furthermore, we discovered that sorcin interacted with PAX5 in the cytoplasm and inhibited PAX5 nuclear translocation, which in turn decreased FBXL12 protein expression and then reduced ALDH1A1 ubiquitination, thus inhibiting ferroptosis. Moreover, an in-house natural product screen revealed that celastrol inhibited the interaction of sorcin and PAX5 by directly binding to the Cys194 residue of the sorcin protein; disruption of the sorcin-PAX5 interaction promoted the nuclear translocation of PAX5, induced the expression of FBXL12, increased the ubiquitylation of ALDH1A1, and eventually induced ferroptosis in pancreatic cancer cells.

CONCLUSION

In this study, we revealed the mechanism of action of sorcin, which is a druggable target for inducing ferroptosis, we identified celastrol as a novel agent that induces ferroptosis, and we showed that disrupting the sorcin-PAX5 interaction is a promising therapeutic strategy for treating pancreatic cancer.

Mechanism study of ubiquitination in T cell development and autoimmune disease

T cells play critical role in multiple immune processes including antigen response, tumor immunity, inflammation, self-tolerance maintenance and autoimmune diseases et. Fetal liver or bone marrow-derived thymus-seeding progenitors (TSPs) settle in thymus and undergo T cell-lineage commitment, proliferation, T cell receptor (TCR) rearrangement, and thymic selections driven by microenvironment composed of thymic epithelial cells (TEC), dendritic cells (DC), macrophage and B cells, thus generating T cells with diverse TCR repertoire immunocompetent but not self-reactive. Additionally, some self-reactive thymocytes give rise to Treg with the help of TEC and DC, serving for immune tolerance. The sequential proliferation, cell fate decision, and selection during T cell development and self-tolerance establishment are tightly regulated to ensure the proper immune response without autoimmune reaction. There are remarkable progresses in understanding of the regulatory mechanisms regarding ubiquitination in T cell development and the establishment of self-tolerance in the past few years, which holds great potential for further therapeutic interventions in immune-related diseases.

The Function of Ubiquitination in T-Cell Development

Thymus is an important primary lymphoid organ for T cell development. After T-lineage commitment, the early thymic progenitors (ETPs) develop into CD4-CD8- (DN), CD4+CD8+ (DP) and further CD4+ SP or CD8+ SP T cells. Under the help of thymic epithelial cells (TEC), dendritic cell (DC), macrophage, and B cells, ETPs undergo proliferation, T cell receptor (TCR) rearrangement, β-selection, positive selection, and negative selection, and thus leading to the generation of T cells that are diverse repertoire immunocompetent but not self-reactive. Additionally, some self-reactive thymocytes give rise to Treg under the help of TEC and DC. The regulation of T cell development is complicated. As a post-translational modification, ubiquitination regulates signal transduction in diverse biological processes. Ubiquitination functions in T cell development through regulating key signal pathway or maturation and function of related cells. In this review, the regulation of T cell development by ubiquitination is summarized and discussed.

Analyses of selected tumour-associated factors expression in normotensive and preeclamptic placenta

INTRODUCTION

Human placenta is often considered a controlled-tumour because of shared properties such as invasion and angiogenesis. We assessed the status of a few selected tumour-associated factors (TAFs) in late onset pre-eclamptic (PE) and normotensive (NT) placentae, to understand their involvement in trophoblast invasion. These molecules include aldehyde dehydrogenase (ALDH3A1), aurora kinases (AURK-A/C), platelet derived growth factor receptor-α (PDGFRα), jagged-1 (JAG1) and twist related protein-1 (TWIST1).

METHODS

The expression of TAF was compared in 13 NT and 11 PE (late onset) placentae using immunoblotting/immunohistochemistry. We then used a novel spheroidal cell model developed from transformed human first trimester trophoblast cell lines HTR8/SVneo and TEV-1 to determine the expression and localization of these six factors during invasion. We also compared the expression of these TAFs during migration and invasion.

RESULTS

Our results suggest that expressions of ALDH3A1, AURK-A, PDGFRα, and TWIST1 are significantly upregulated in PE placentae (p < 0.05) when compared to NT placentae, whereas AURK-C and JAG1 are down-regulated (p < 0.05). The protein expression pattern of all the six factors were found to be similar in spheroids in comparison to their parental counterparts. The invasive potential of the spheroids was also enhanced when compared with the parental cells.

DISCUSSION

Collectively, data from our present study suggests that these TAFs are involved in placental invasion and their altered expressions may be regarded as a compensatory mechanism against reduced invasion.

F-box proteins in cancer stemness: An emerging prognostic and therapeutic target

Cancer is a complex heterogenic disease with significant therapeutic challenges. The presence of cancer stem cells (CSCs) in cancer tissue orchestrates tumor growth, progression, and metastasis, the tumor heterogeneity, disease relapse, and therapeutic resistance. Hence, it is imperative to explore how progenitor or cancer-initiating cells acquire stemness features and reprogram different biological mechanisms to maintain their sustained oncogenicity. Interestingly, deregulation of F-box proteins (FBPs) is crucial for cancer stemness features, including drug resistance and disease relapse. In this review, we highlight recent updates on the clinical significance of targeting FBPs in cancer therapy, with emphasis on eliminating CSCs and associated therapeutic challenges. Moreover, we also discuss novel strategies for the selective elimination of CSCs by targeting FBPs.

Skp2 contributes to cell cycle progression in trophoblast stem cells and to placental development

All trophoblast subtypes of the placenta are derived from trophoblast stem cells (TSCs). TSCs have the capacity to self-renew, but how the proliferation of these cells is regulated in the undifferentiated state has been largely unclear. We now show that the F-box protein Skp2 regulates the proliferation of TSCs and thereby plays a pivotal role in placental development in mice on the C57BL/6 background. The placenta of Skp2^-/- mouse embryos on the C57BL/6 background was smaller than that of their Skp2^+/+ littermates, with the mutant embryos also manifesting intrauterine growth retardation. Although the Skp2^-/- mice were born alive, most of them died before postnatal day 21, presumably as a result of placental defects. Depletion of Skp2 in TSCs cultured in the undifferentiated state resulted in a reduced rate of proliferation and arrest of the cell cycle in G₁ phase, indicative of a defect in self-renewal capacity. The cell cycle arrest apparent in Skp2-deficient TSCs was reversed by additional ablation of the cyclin-dependent kinase inhibitor (CKI) p57 but not by that of the CKI p27. Our results thus suggest that Skp2-mediated degradation of p57 is an important determinant of the self-renewal capacity of TSCs during placental development, at least in mice of certain genetic backgrounds.

Knockout Mouse Models Provide Insight into the Biological Functions of CRL1 Components

The CRL1 complex, also known as the SCF complex, is a ubiquitin ligase that in mammals consists of an adaptor protein (SKP1), a scaffold protein (CUL1), a RING finger protein (RBX1, also known as ROC1), and one of about 70 F-box proteins. Given that the F-box proteins determine the substrate specificity of the CRL1 complex, the variety of these proteins allows the generation of a large number of ubiquitin ligases that promote the degradation or regulate the function of many substrate proteins and thereby control numerous key cellular processes. The physiological and pathological functions of these many CRL1 ubiquitin ligases have been studied by the generation and characterization of knockout mouse models that lack specific CRL1 components. In this chapter, we provide a comprehensive overview of these mouse models and discuss the role of each CRL1 component in mouse physiology and pathology.

Blastocyst transfer in mice alters the placental transcriptome and growth

Assisted reproduction technologies (ART) are becoming increasingly common. Therefore, how these procedures influence gene regulation and feto-placental development are important to explore. Here, we assess the effects of blastocyst transfer on mouse placental growth and transcriptome. C57Bl/6 blastocysts were transferred into uteri of B6D2F1 pseudopregnant females and dissected at embryonic day 10.5 for analysis. Compared to non-transferred controls, placentas from transferred conceptuses weighed less even though the embryos were larger on average. This suggested a compensatory increase in placental efficiency. RNA-sequencing of whole male placentas revealed 543 differentially expressed genes (DEGs) after blastocyst transfer: 188 and 355 genes were down-regulated and up-regulated, respectively. DEGs were independently validated in male and female placentas. Bioinformatic analyses revealed that DEGs represented expression in all major placental cell types and included genes that are critical for placenta development and/or function. Furthermore, the direction of transcriptional change in response to blastocyst transfer implied an adaptive response to improve placental function to maintain fetal growth. Our analysis revealed that CpG methylation at regulatory regions of two DEGs was unchanged in female transferred placentas and that DEGs had fewer gene-associated CpG islands (within ~20 kb region) compared to the larger genome. These data suggested that altered methylation at proximal promoter regions might not lead to transcriptional disruption in transferred placentas. Genomic clustering of some DEGs warrants further investigation of long-range, cis-acting epigenetic mechanisms including histone modifications together with DNA methylation. We conclude that embryo transfer, a protocol required for ART, significantly impacts the placental transcriptome and growth.

Notch and the pre-TCR coordinate thymocyte proliferation by induction of the SCF subunits Fbxl1 and Fbxl12

Proliferation is tightly regulated during T cell development and is limited to immature CD4⁻CD8⁻ thymocytes. The major proliferative event is initiated at the ‘β-selection’ stage following successful rearrangement of Tcrβ and is triggered by and dependent on concurrent signaling by Notch and the pre-TCR; however, it is unclear how these signals cooperate to promote cell proliferation. Here we found that β-selection-associated proliferation required the combined activity of two SCF ubiquitin ligase complexes that included as substrate recognition subunits the F-box proteins Fbxl1 or Fbxl12. Both SCF complexes targeted the cyclin-dependent kinase inhibitor Cdkn1b for ubiquitinylaton and degradation. We found that Notch signals induced the transcription of Fbxl1 whereas pre-TCR signals induced the transcription of Fbxl12. Thus, concurrent Notch and pre-TCR signaling induced the expression of two genes, Fbxl1 and Fbxl12, whose products functioned identically but additively to promote degradation of Cdkn1b, cell cycle progression, and proliferation of β-selected thymocytes.

Aldehyde dehydrogenase isoforms and inflammatory cell populations are differentially expressed in term human placentas affected by intrauterine growth restriction

OBJECTIVE

Intrauterine growth restriction (IUGR) is a complication of pregnancy that has both short- and long-term sequelae for affected mothers and offspring. The pathophysiology of disease stems from poor nutrient and oxygen provision to the fetus, resulting in increased oxidative stress within the placenta. As the milieu within the local microenvironment alters macrophage differentiation, we hypothesized that macrophage plasticity may be altered in placentas associated with IUGR, and that macrophages would show hallmarks of lipid peroxidation including altered aldehyde metabolism.

METHODS

In human placentas taken from normal pregnancies resulting in appropriate-for-gestational-age (AGA) newborns and placentas associated with IUGR, placental macrophages were evaluated by immunohistochemistry and shown in IUGR to resemble pro-inflammatory activated M1-type macrophages. To link oxidative stress to macrophages, the expression of aldehyde dehydrogenase (ALDHs) isozymes ALDH1, ALDH2, and ALDH3 was assessed.

RESULTS

All three isozymes displayed preferential staining for distinct cellular populations within the term human placenta. ALDH1 and ALDH2 were strongly expressed in placental Hofbauer and decidual stromal cells. ALDH3, in contrast, was present in extravillous trophoblasts. Comparing AGA and IUGR-associated placentas, ALDH1 and ALDH2 trended to have greater expression in macrophage populations but lower expression in decidual cell populations in IUGR-associated placentas. ALDH3 had higher expression in IUGR-associated placentas but localized specifically to extravillous trophoblast populations.

CONCLUSION

Therefore, we speculate that specific ALDH isozymes have cell-specific functions related to differentiation, inflammation, or oxidative stress responses that are altered in IUGR-associated term human placentas. This family of isozymes may be a novel method to identify human placentas affected by placental insufficiency/IUGR.

Aldehyde dehydrogenase 1B1: a novel immunohistological marker for colorectal cancer

Background:

Aldehyde dehydrogenase (ALDH) 1A1 is an immunohistological biomarker of various solid tumours, but has not been successfully proved as a colorectal cancer (CRC) marker. We recently reported that ALDH1B1, which has functional roles in tumourigenesis, may be a better CRC marker than ALDH1A1.

Methods:

Human CRC explants and cell lines were analysed to identify candidate CRC markers from eight ALDH isozymes including ALDH1A1 and ALDH1B1. A tissue microarray, including paired specimens of normal and tumour tissues, was subsequently analysed to determine if candidate ALDHs could distinguish CRC from normal tissue.

Results:

Based on mRNA analysis, ALDH1B1 and ALDH2 were selected as suitable candidates. These were strongly and regularly expressed in tumour tissue and cell lines, including highly tumourigenic cell populations (ALDH⁺CD44⁺ cells), while other ALDHs, including ALDH1A1, showed differential or low expression. No genetic alteration of ALDH1B1 in CRC was suggested by the relationships between mRNA and protein levels/enzymatic activities, and cDNA sequences of CRC cell lines. Tissue microarray findings showed that ALDH1B1, but not ALDH2, could distinguish CRC from normal tissue. Furthermore, ratios of ALDH1B1 to ALDH1A1 or ALDH2 were found to be powerful CRC indicators.

Conclusions:

These results suggest that ALDH1B1 is a novel human CRC biomarker.

SCFFbl12 Increases p21Waf1/Cip1 Expression Level through Atypical Ubiquitin Chain Synthesis

The cyclin-dependent kinase (CDK) inhibitor p21 is an unstructured protein regulated by multiple turnover pathways. p21 abundance is tightly regulated, and its defect causes tumor development. However, the mechanisms that underlie the control of p21 level are not fully understood. Here, we report a novel mechanism by which a component of the SCF ubiquitin ligase, Fbl12, augments p21 via the formation of atypical ubiquitin chains. We found that Fbl12 binds and ubiquitinates p21. Unexpectedly, Fbl12 increases the expression level of p21 by enhancing the mixed-type ubiquitination, including not only K48- but also K63-linked ubiquitin chains, followed by promotion of binding between p21 and CDK2. We also found that proteasome activator PA28γ attenuates p21 ubiquitination by interacting with Fbl12. In addition, UV irradiation induces a dissociation of p21 from Fbl12 and decreases K63-linked ubiquitination, leading to p21 degradation. These data suggest that Fbl12 is a key factor that maintains adequate intracellular concentration of p21 under normal conditions. Our finding may provide a novel possibility that p21's fate is governed by diverse ubiquitin chains.