Critical function for SIP, a ubiquitin E3 ligase component of the beta-catenin degradation pathway, for thymocyte development and G1 checkpoint

Ubiquitination of NS1 Confers Differential Adaptation of Zika Virus in Mammalian Hosts and Mosquito Vectors

Arboviruses, transmitted by medical arthropods, pose a serious health threat worldwide. During viral infection, Post Translational Modifications (PTMs) are present on both host and viral proteins, regulating multiple processes of the viral lifecycle. In this study, a mammalian E3 ubiquitin ligase WWP2 (WW domain containing E3 ubiquitin ligase 2) is identified, which interacts with the NS1 protein of Zika virus (ZIKV) and mediates K63 and K48 ubiquitination of Lys 265 and Lys 284, respectively. WWP2-mediated NS1 ubiquitination leads to NS1 degradation via the ubiquitin-proteasome pathway, thereby inhibiting ZIKV infection in mammalian hosts. Simultaneously, it is found Su(dx), a protein highly homologous to host WWP2 in mosquitoes, is capable of ubiquitinating NS1 in mosquito cells. Unexpectedly, ubiquitination of NS1 in mosquitoes does not lead to NS1 degradation; instead, it promotes viral infection in mosquitoes. Correspondingly, the NS1 K265R mutant virus is less infectious to mosquitoes than the wild-type (WT) virus. The above results suggest that the ubiquitination of the NS1 protein confers different adaptations of ZIKV to hosts and vectors, and more importantly, this explains why NS1 K265-type strains have become predominantly endemic in nature. This study highlights the potential application in antiviral drug and vaccine development by targeting viral proteins' PTMs.

Proteomics of severe SARS-COV-2 infection and paraquat poisoning in human lung tissue samples: comparison of microbial infected and toxic pulmonary fibrosis

Introduction

Pulmonary fibrosis (PF) encompasses a spectrum of lung conditions characterized by the abnormal accumulation of scar tissue in the lungs, leading to impaired respiratory function. Various conditions can result in severe PF, among which viral infections have emerged as significant triggers. In addition to viral infections, exposure to toxic substances such as paraquat represents another significant risk factor for PF. Therefore, this study aimed to explore the dissimilarities and similarities between PF triggered by viral infections and chemical toxicants, using the mechanism of PF in IPF as a reference.

Methods

Data-independent acquisition proteomics technology was employed to identify COVID-19 and paraquat-induced PF from the autopsy of lung tissue samples obtained from individuals who died due to PF. Bioinformatics was employed for differential protein analysis, and selected indicators were validated on pathological sections.

Results

Our results showed that the differential proteins associated with the two causes of PF were enriched in similar lung fibrosis-related signaling pathways, such as the Wnt signaling pathway. However, differences were observed in proteins such as CACYBP, we verified the consistency of the results with proteomics using the IHC approach.

Conclusion

This study illuminates distinct protein-level differences by investigating pulmonary fibrosis pathways in severe COVID-19 and paraquat poisoning. Although both conditions activate lung-protective and repair pathways, COVID-19 shows limited phosphorylation-independent ubiquitination of β-catenin compared to paraquat toxicity. These findings shed light on potential therapeutic targets for PF induced via diverse factors.

Involvement of CacyBP/SIP in differentiation and the immune response of HaCaT keratinocytes

CacyBP/SIP is a multifunctional protein present in various cells and tissues. However, its expression and role in the epidermis has not been explored so far. In this work, using RT-qPCR, Western blot analysis and three-dimensional (3D) organotypic cultures of HaCaT keratinocytes we show that CacyBP/SIP is present in the epidermis. To investigate the possible role of CacyBP/SIP in keratinocytes we obtained CacyBP/SIP knockdown cells and studied the effect of CacyBP/SIP deficiency on their differentiation and response to viral infection. We found that CacyBP/SIP knockdown results in reduced expression of epidermal differentiation markers in both undifferentiated and differentiated HaCaT cells. Since epidermis is engaged in immune defense, the impact of CacyBP/SIP knockdown on this process was also analyzed. By applying RT-qPCR and Western blot it was found that poly(I:C), a synthetic analog of double-stranded RNA that mimics viral infection, stimulated the expression of genes involved in antiviral response, such as IFIT1, IFIT2 and OASL. Interestingly, following poly(I:C) stimulation, the level of expression of these genes was significantly lower in cells with CacyBP/SIP knockdown than control ones. Since the signaling pathway mediating cellular responses to viral infection involves, among others, the STAT1 transcription factor, we measured its activity using luciferase assay and found that it was lower in CacyBP/SIP knockdown HaCaT cells. Altogether, the presented results indicate that CacyBP/SIP promotes epidermal differentiation and might be involved in response of the skin cells to viral infection.

ANXA11 mutations are associated with amyotrophic lateral sclerosis–frontotemporal dementia

Background

The Annexin A11 (ANXA11) gene has been newly identified as a causative gene of amyotrophic lateral sclerosis (ALS) with or without frontotemporal dementia (FTD). The current study aimed to investigate the ANXA11 mutations in a Chinese ALS–FTD or FTD cohort.

Methods

We included ten probands/patients with suspected ALS–FTD or FTD. Mutational analysis of ANXA11 was performed through Next Generation Sequencing (NGS) and Sanger sequencing. We collected and reviewed clinical presentation, neuropsychology test results, brain-imaging findings, and electrophysiological examination findings.

Results

In total, six probands presented with ALS–FTD, and four with behavior variant FTD (bv-FTD). We identified a non-synonymous heterozygous mutation (c.119A>G, p.D40G) of ANXA11 in proband 1, which is associated with ALS. However, this is the first report of the mutation causing ALS–FTD. Proband 1 started with abnormal behavior and progressed to classic upper motor nervous disease. Magnetic resonance imaging (MRI) showed significant bilateral temporal lobe atrophy and bilateral hyperintensities along the corticospinal tracts.18F-AV45-PET imaging showed negative amyloid deposits.

Conclusion

ANXA11-related diseases have high clinical and genetic heterogeneity. Our study confirmed the contribution of ANXA11 mutations to ALS–FTD. The ANXA11 mutations established a complex genotype–phenotype correlation in ALS–FTD. Our research further elucidated the genetic mechanism of ALS–FTD and contributed to setting the foundation of future targeted therapy.

Heterozygous calcyclin-binding protein/Siah1-interacting protein (CACYBP/SIP) gene pathogenic variant linked to a dominant family with paucity of interlobular bile duct

Paucity of interlobular bile ducts (PILBD) is a heterogeneous disorder classified into two categories, syndromic and non-syndromic bile duct paucity. Syndromic PILBD is characterized by the presence of clinical manifestations of Alagille syndrome. Non-syndromic PILBD is caused by multiple diseases, such as metabolic and genetic disorders, infectious diseases, and inflammatory and immune disorders. We evaluated a family with a dominantly inherited PILBD, who presented with cholestasis at 1-2 months of age but spontaneously improved by 1 year of age. Next-generation sequencing analysis revealed a heterozygous CACYBP/SIP p.E177Q pathogenic variant. Calcyclin-binding protein and Siah1 interacting protein (CACYBP/SIP) form a ubiquitin ligase complex and induce proteasomal degradation of non-phosphorylated β-catenin. Immunohistochemical analysis revealed a slight decrease in CACYBP and β-catenin levels in the liver of patients in early infancy, which almost normalized by 13 months of age. The CACYBP/SIP p.E177Q pathogenic variant may form a more active or stable ubiquitin ligase complex that enhances the degradation of β-catenin and delays the maturation of intrahepatic bile ducts. Our findings indicate that accurate regulation of the β-catenin concentration is essential for the development of intrahepatic bile ducts and CACYBP/SIP pathogenic variant is a novel cause of PILDB.

Regulatory mechanism of cyclins and cyclin-dependent kinases in post-mitotic neuronal cell division

Neurodegenerative diseases (NDDs) are the most common life-threatening disease of the central nervous system and it cause the progressive loss of neuronal cells. The exact mechanism of the disease's progression is not clear and thus line of treatment for NDDs is a baffling issue. During the progression of NDDs, oxidative stress and DNA damage play an important regulatory function, and ultimately induces neurodegeneration. Recently, aberrant cell cycle events have been demonstrated in the progression of different NDDs. However, the pertinent role of signaling mechanism, for instance, post-translational modifications, oxidative stress, DNA damage response pathway, JNK/p38 MAPK, MEK/ERK cascade, actively participated in the aberrant cell cycle reentry induced neuronal cell death. Mounting evidence has demonstrated that aberrant cell cycle re-entry is a major contributing factor in the pathogenesis of NDDs rather than a secondary phenomenon. In the brain of AD patients with mild cognitive impairment, post miotic cell division can be seen in the early stage of the disease. However, in the brain of PD patients, response to various neurotoxic signals, the cell cycle re-entry has been observed that causes neuronal apoptosis. On contrary, the contributing factors that leads to the induction of cell cycle events in mature neurons in HD and ALS brain pathology is remain unclear. Various pharmacological drugs have been developed to reduce the pathogenesis of NDDs, but they are still not helpful in eliminating the cause of these NDDs.

Investigating Mechanisms of Response or Resistance to Immune Checkpoint Inhibitors by Analyzing Cell-Cell Communications in Tumors Before and After Programmed Cell Death-1 (PD-1) Targeted Therapy: An Integrative Analysis Using Single-cell RNA and Bulk-RNA Sequencing Data

Currently, a significant proportion of cancer patients do not benefit from programmed cell death-1 (PD-1)-targeted therapy. Overcoming drug resistance remains a challenge. In this study, single-cell RNA sequencing and bulk RNA sequencing data from samples collected before and after anti-PD-1 therapy were analyzed. Cell-cell interaction analyses were performed to determine the differences between pretreatment responders and nonresponders and the relative differences in changes from pretreatment to posttreatment status between responders and nonresponders to ultimately investigate the specific mechanisms underlying response and resistance to anti-PD-1 therapy. Bulk-RNA sequencing data were used to validate our results. Furthermore, we analyzed the evolutionary trajectory of ligands/receptors in specific cell types in responders and nonresponders. Based on pretreatment data from responders and nonresponders, we identified several different cell-cell interactions, like WNT5A-PTPRK, EGFR-AREG, AXL-GAS6 and ACKR3-CXCL12. Furthermore, relative differences in the changes from pretreatment to posttreatment status between responders and nonresponders existed in SELE-PSGL-1, CXCR3-CCL19, CCL4-SLC7A1, CXCL12-CXCR3, EGFR-AREG, THBS1-a3b1 complex, TNF-TNFRSF1A, TNF-FAS and TNFSF10-TNFRSF10D interactions. In trajectory analyses of tumor-specific exhausted CD8 T cells using ligand/receptor genes, we identified a cluster of T cells that presented a distinct pattern of ligand/receptor expression. They highly expressed suppressive genes like HAVCR2 and KLRC1, cytotoxic genes like GZMB and FASLG and the tissue-residence-related gene CCL5. These cells had increased expression of survival-related and tissue-residence-related genes, like heat shock protein genes and the interleukin-7 receptor (IL-7R), CACYBP and IFITM3 genes, after anti-PD-1 therapy. These results reveal the mechanisms underlying anti-PD-1 therapy response and offer abundant clues for potential strategies to improve immunotherapy.

TRAF4, a new substrate of SIAH1, participates in chemotherapy resistance of breast cancer cell by counteracting SIAH1-mediated downregulation of β-catenin

PURPOSE

TRAF4 plays an important role in the development and progression of breast cancer, but its impact on chemotherapy resistance is as yet, however, poorly understood.

METHODS

Western blotting, immunoprecipitation, and immunofluorescence staining were used to identify and verify that TRAF4 was a novel substrate of SIAH1 and prevented SIAH1-mediated β-catenin degradation. Cell proliferation analysis and Flow cytometry analysis were utilized to detect TRAF4's function on the growth-inhibitory effect of etoposide. Immunohistochemistry was used to detect the expression of TRAF4, SIAH1, and β-catenin. Statistical analysis was used to analyze the relationships between them with clinical parameters and curative effect of chemotherapy pathologically.

RESULTS

Our results suggested that TRAF4 prevents SIAH1-mediated β-catenin degradation. TRAF4 was a novel substrate of SIAH1 and the TRAF domain of TRAF4 was critical for binding to SIAH1. TRAF4 reduced the growth-inhibitory effect of etoposide via reducing the number of S-phase cells and suppressing cell apoptosis. Concordantly, we found that breast cancer patients with a low-TRAF4 expression benefited most from chemotherapy, who had higher tumor volume reduction rate and better pathological response, while, the high-TRAF4 expression group had lower tumor volume reduction rate and poor pathological response.

CONCLUSIONS

TRAF4 was a novel substrate of SIAH1 and prevented SIAH1-mediated β-catenin degradation, which explains the protective effect of TRAF4 on β-catenin during cell stress and links TRAF4 to chemotherapy resistance in tumors. These findings implicated a novel pathway for the oncogenic function of TRAF4.

Comparative evaluation of CacyBP/SIP protein, β-catenin, and immunoproteasome subunit LMP7 in the heart of rats with hypertension of different etiology

Calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP) is the recently discovered peptide, which participates in various intracellular processes. Recent reports indicated that CacyBP/SIP activates the ubiquitin ligases and promotes proteasomal degradation of proteins. One of the most important proteins degraded in CacyBP/SIP-dependent pathway is β-catenin. Considering the key importance of β-catenin in the functioning of the cardiovascular system and in the view of the close relationship between CacyBP/SIP, β-catenin, and proteasomal activity, we have decided to undertake research to identify and evaluate the distribution of CacyBP/SIP, β-catenin and the LMP7 subunit of the immunoproteasome in the heart of rats with hypertension of various etiology. The studies were carried out on the hearts of rats with spontaneous hypertension (SHR), renovascular hypertension, and DOCA-salt hypertension. The myocardial expression of CacyBP/SIP, β-catenin, and LMP7 was detected by immunohistochemistry using the EnVision method. The hypertension significantly increased the immunoreactivity to CacyBP/SIP and LMP-7, while weakening the β-catenin immunoreaction. The intensity of the observed changes depends on the type of hypertension. Our results show an innovative and important network of interactions between proteins potentially involved in the development and progression of heart problems in various types of hypertension. This report might contribute to deeper understanding of the role of the CacyBP/SIP protein, β-catenin, and immunoproteasomes in heart function, as well as to bringing new information concerning pathophysiologic mechanisms leading to cardiac dysfunction in the state of elevated blood pressure.

Impact statement

Despite extensive research into the pathogenesis of hypertension and disease-related end organ damage, the mechanisms leading to cardiac complications of hypertensive patients are still not fully elucidated. The aim of the presented research was immunodetection and evaluation of CacyBP/SIP, β-catenin, and proteasomes in the hearts of rats with hypertension of different etiology. Our results show an innovative and important network of interactions between proteins potentially involved in the development and progression of heart problems in various types of hypertension. This report might contribute to deeper understanding of the role of the CacyBP/SIP protein, β-catenin, and proteasomes in heart function. Our results might also bring new information concerning the intracellular processes and signal pathways involved in the regulation of cardiomyocytes functioning in hypertension state. In addition to cognitive significance, the results of presented studies may contribute to further successes in preventing and treatment of cardiac complications associated with hypertension.

ANXA11 mutations prevail in Chinese ALS patients with and without cognitive dementia

Objective

To investigate the genetic contribution of ANXA11, a gene associated with amyotrophic lateral sclerosis (ALS), in Chinese ALS patients with and without cognitive dementia.

Methods

Sequencing all the coding exons of ANXA11 and intron-exon boundaries in 18 familial amyotrophic lateral sclerosis (FALS), 353 unrelated sporadic amyotrophic lateral sclerosis (SALS), and 12 Chinese patients with ALS-frontotemporal lobar dementia (ALS-FTD). The transcripts in peripheral blood generated from a splicing mutation were examined by reverse transcriptase PCR.

Results

We identified 6 nonsynonymous heterozygous mutations (5 novel and 1 recurrent), 1 splice site mutation, and 1 deletion of 10 amino acids (not accounted in the mutant frequency) in 11 unrelated patients, accounting for a mutant frequency of 5.6% (1/18) in FALS, 2.3% (8/353) in SALS, and 8.3% (1/12) in ALS-FTD. The deletion of 10 amino acids was detected in 1 clinically undetermined male with an ALS family history who had atrophy in hand muscles and myotonic discharges revealed by EMG. The novel p. P36R mutation was identified in 1 FALS index, 1 patient with SALS, and 1 ALS-FTD. The splicing mutation (c.174-2A>G) caused in-frame skipping of the entire exon 6. The rest missense mutations including p.D40G, p.V128M, p.S229R, p.R302C and p.G491R were found in 6 unrelated patients with SALS.

Conclusions

The ANXA11 gene is one of the most frequently mutated genes in Chinese patients with SALS. A canonical splice site mutation leading to skipping of the entire exon 6 further supports the loss-of-function mechanism. In addition, the study findings further expand the ANXA11 phenotype, first highlighting its pathogenic role in ALS-FTD.

Transcriptional regulation of CacyBP/SIP gene and the influence of increased CacyBP/SIP level on gene expression pattern in colorectal cancer HCT116 cells

The CacyBP/SIP protein is expressed at a particularly high level in brain, spleen, and various tumors. In this work, we have studied transcriptional regulation of the CacyBP/SIP gene and the influence of increased CacyBP/SIP level on gene expression in colorectal cancer HCT116 cells. We have shown that E2F1, EGR1, and CREB transcription factors bind to the CacyBP/SIP gene promoter and stimulate transcription of CacyBP/SIP gene. The role of CREB was further confirmed by the observation that forskolin, a strong activator of CREB phosphorylation/activity, increased CacyBP/SIP gene promoter activity. Moreover, we have shown that CREB dominant negative mutants, CREB133 and KCREB, inhibits CacyBP/SIP promoter activity. To check the biological significance of increased CacyBP/SIP expression/level we have applied RNA microarray analysis and have found that upregulation of CacyBP/SIP entails changes in mRNA level of many genes involved, among others, in immune processes. © 2017 IUBMB Life, 70(1):50-59, 2018.

Regulation of CacyBP/SIP expression by NFAT1 transcription factor

In this work we have shown that NFAT1 transcription factor is involved in the regulation of CacyBP/SIP expression. We have demonstrated, by applying Western blot, RT-PCR and luciferase assay that the level of CacyBP/SIP increases upon NFAT1 overexpression. Moreover, inhibition or stimulation of NFAT transcriptional activity exerts a corresponding effect on the expression of CacyBP/SIP gene. Furthermore, EMSA and chromatin immunoprecipitation (ChIP) assay have shown that NFAT1 binds to its specific binding sites within the CacyBP/SIP gene. In conclusion, our data have shown for the first time the regulation of CacyBP/SIP gene expression by NFAT1. Since NFAT transcription factors are involved in processes related to immune response, these results indicate potential involvement of CacyBP/SIP in the immune system.

Mutations in the vesicular trafficking protein annexin A11 are associated with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder. We screened 751 familial ALS patient whole-exome sequences and identified six mutations including p.D40G in the ANXA11 gene in 13 individuals. The p.D40G mutation was absent from 70,000 control whole-exome sequences. This mutation segregated with disease in two kindreds and was present in another two unrelated cases (P = 0.0102), and all mutation carriers shared a common founder haplotype. Annexin A11-positive protein aggregates were abundant in spinal cord motor neurons and hippocampal neuronal axons in an ALS patient carrying the p.D40G mutation. Transfected human embryonic kidney cells expressing ANXA11 with the p.D40G mutation and other N-terminal mutations showed altered binding to calcyclin, and the p.R235Q mutant protein formed insoluble aggregates. We conclude that mutations in ANXA11 are associated with ALS and implicate defective intracellular protein trafficking in disease pathogenesis.

Ubiquitination and the Regulation of Membrane Proteins

Newly synthesized transmembrane proteins undergo a series of steps to ensure that only the required amount of correctly folded protein is localized to the membrane. The regulation of protein quality and its abundance at the membrane are often controlled by ubiquitination, a multistep enzymatic process that results in the attachment of ubiquitin, or chains of ubiquitin to the target protein. Protein ubiquitination acts as a signal for sorting, trafficking, and the removal of membrane proteins via endocytosis, a process through which multiple ubiquitin ligases are known to specifically regulate the functions of a number of ion channels, transporters, and signaling receptors. Endocytic removal of these proteins through ubiquitin-dependent endocytosis provides a way to rapidly downregulate the physiological outcomes, and defects in such controls are directly linked to human pathologies. Recent evidence suggests that ubiquitination is also involved in the shedding of membranes and associated proteins as extracellular vesicles, thereby not only controlling the cell surface levels of some membrane proteins, but also their potential transport to neighboring cells. In this review, we summarize the mechanisms and functions of ubiquitination of membrane proteins and provide specific examples of ubiquitin-dependent regulation of membrane proteins.

The potential role of CacyBP/SIP in tumorigenesis

Calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP) was initially described as a binding partner of S100A6 in the Ehrlich ascites tumor cells and later as a Siah-1-interacting protein. This 30 kDa protein includes three domains and is involved in cell proliferation, differentiation, cytoskeletal rearrangement, and transcriptional regulation via binding to various proteins. Studies have also shown that the CacyBP/SIP is a critical protein in tumorigenesis. But, its promotion or suppression of cancer progression may depend on the cell type. In this review, the biological characteristics and target proteins of CacyBP/SIP have been described. Moreover, the exact role of CacyBP/SIP in various cancers is discussed.

CacyBP/SIP--Structure and variety of functions

BACKGROUND

CacyBP/SIP (Calcyclin-Binding Protein and Siah-1 Interacting Protein) is a small modular protein implicated in a wide range of cellular processes. It is expressed in different tissues of mammals but homologs are also found in some lower organisms. In mammals, a high level of CacyBP/SIP is present in tumor cells and in neurons. CacyBP/SIP binds several target proteins such as members of the S100 family, components of a ubiquitin ligase complex, and cytoskeletal proteins.

SCOPE OF REVIEW

CacyBP/SIP has been shown to be involved in protein de-phosphorylation, ubiquitination, cytoskeletal dynamics, regulation of gene expression, cell proliferation, differentiation, and tumorigenesis. This review focuses on very recent reports on CacyBP/SIP structure and function in these important cellular processes.

MAJOR CONCLUSIONS

CacyBP/SIP is a multi-domain and multi-functional protein. Altered levels of CacyBP/SIP in several cancers implicate its involvement in the maintenance of cell homeostasis. Changes in CacyBP/SIP subcellular localization in neurons of AD brains suggest that this protein is strongly linked to neurodegenerative diseases. Elucidation of CacyBP/SIP structure and cellular function is leading to greater understanding of its role in normal physiology and disease pathologies.

GENERAL SIGNIFICANCE

The available results suggest that CacyBP/SIP is a key player in multiple biological processes. Detailed characterization of the physical, biochemical and biological properties of CacyBP/SIP will provide better insight into the regulation of its diverse functions in vivo, and given the association with specific diseases, will help clarify the potential of therapeutic targeting of this protein.

Calcyclin-binding protein/Siah-1-interacting protein as a regulator of transcriptional responses in brain cells

The calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP) is highly expressed in the brain and has been shown to regulate β-catenin-driven transcription in thymocytes. Therefore, we investigated whether CacyBP/SIP plays a role as a transcriptional regulator in brain cells. In brain-derived neurotrophic factor (BDNF)- and forskolin-stimulated rat primary cortical neurons, overexpression of CacyBP/SIP enhanced transcriptional activity of the cAMP-response element (CRE). In addition, overexpressed CacyBP/SIP enhanced BDNF-mediated activation of the nuclear factor of activated T cells (NFAT) but not the serum response element (SRE). These stimulatory effects required an intact C-terminal domain of CacyBP/SIP. Moreover, in C6 rat glioma cells, the overexpressed CacyBP/SIP enhanced activation of CRE and NFAT following forskolin and serum stimulation, respectively. Conversely, knockdown of endogenous CacyBP/SIP reduced activation of CRE and NFAT but not of SRE. Taken together, these results indicate that CacyBP/SIP is a novel regulator of CRE- and NFAT-driven transcription.

CacyBP/SIP nuclear translocation induced by gastrin promotes gastric cancer cell proliferation

AIM: To investigate the role of nuclear translocation of calcyclin binding protein, also called Siah-1 interacting protein (CacyBP/SIP), in gastric carcinogenesis.

METHODS: The expression of CacyBP/SIP protein in gastric cancer cell lines was detected by Western blot. Immunofluorescence experiments were performed on gastric cancer cell lines that had been either unstimulated or stimulated with gastrin. To confirm the immunofluorescence findings, the relative abundance of CacyBP/SIP in nuclear and cytoplasmic compartments was assessed by Western blot. The effect of nuclear translocation of CacyBP/SIP on cell proliferation was examined using MTT assay. The colony formation assay was used to measure clonogenic cell survival. The effect of CacyBP/SIP nuclear translocation on cell cycle progression was investigated. Two CacyBP/SIP-specific siRNA vectors were designed and constructed to inhibit CacyBP/SIP expression in order to reduce the nuclear translocation of CacyBP/SIP, and the expression of CacyBP/SIP in stably transfected cells was determined by Western blot. The effect of inhibiting CacyBP/SIP nuclear translocation on cell proliferation was then assessed.

RESULTS: CacyBP/SIP protein was present in most of gastric cancer cell lines. In unstimulated cells, CacyBP/SIP was distributed throughout the cytoplasm; while in stimulated cells, CacyBP/SIP was found mainly in the perinuclear region. CacyBP/SIP nuclear translocation generated a growth-stimulatory effect on cells. The number of colonies in the CacyBP/SIP nuclear translocation group was significantly higher than that in the control group. The percentage of stimulated cells in G1 phase was significantly lower than that of control cells (69.70% ± 0.46% and 65.80% ± 0.60%, control cells and gastrin-treated SGC7901 cells, P = 0.008; 72.99% ± 0.46% and 69.36% ± 0.51%, control cells and gastrin-treated MKN45 cells, P = 0.022). CacyBP/SIPsi1 effectively down-regulated the expression of CacyBP/SIP, and cells stably transfected by CacyBP/SIPsi1 were then chosen for further cellular assays. In CacyBP/SIPsi1 stably transfected cells, CacyBP/SIP was shown to be distributed throughout the cytoplasm, irregardless of whether they were stimulated or not. After CacyBP/SIP nuclear translocation was reduced, there had no major effect on cell proliferation, as shown by MTT assay. There had no enhanced anchorage-dependent growth upon stimulation, as indicated by colony formation in flat plates. No changes appeared in the percentage of cells in G0-G1 phase in either cell line (71.09% ± 0.16% and 70.86% ± 0.25%, control cells and gastrin-treated SGC7901-CacyBP/SIPsi1 cells, P = 0.101; 74.17% ± 1.04% and 73.07% ± 1.00%, control cells and gastrin-treated MKN45-CacyBP/SIPsi1 cells, P = 0.225).

CONCLUSION: CacyBP/SIP nuclear translocation promotes the proliferation and cell cycle progression of gastric cancer cells.

Expression of S100A6 in rat hippocampus after traumatic brain injury due to lateral head acceleration

In a rat model of traumatic brain injury (TBI), we investigated changes in cognitive function and S100A6 expression in the hippocampus. TBI-associated changes in this protein have not previously been reported. Rat S100A6 was studied via immunohistochemical staining, Western blot, and reverse transcription-polymerase chain reaction (RT-PCR) after either lateral head acceleration or sham. Reduced levels of S100A6 protein and mRNA were observed 1 h after TBI, followed by gradual increases over 6, 12, 24, and 72 h, and then a return to sham level at 14 day. Morris water maze (MWM) test was used to evaluate animal spatial cognition. TBI- and sham-rats showed an apparent learning curve, expressed as escape latency. Although TBI-rats displayed a relatively poorer cognitive ability than sham-rats, the disparity was not significant early post-injury. Marked cognitive deficits in TBI-rats were observed at 72 h post-injury compared with sham animals. TBI-rats showed decreased times in platform crossing in the daily MWM test; the performance at 72 h post-injury was the worst. In conclusion, a reduction in S100A6 may be one of the early events that lead to secondary cognitive decline after TBI, and its subsequent elevation is tightly linked with cognitive improvement. S100A6 may play important roles in neuronal degeneration and regeneration in TBI.

Identification of TMEM131L as a novel regulator of thymocyte proliferation in humans

In this study, we identify transmembrane protein 131-like (TMEM131L) as a novel regulator of thymocyte proliferation and demonstrate that it corresponds to a not as yet reported inhibitor of Wnt signaling. Short hairpin RNA-mediated silencing of TMEM131L in human CD34(+) hematopoietic progenitors, which were then grafted in NOD-SCID/IL-2rγ(null) mice, resulted in both thymocyte hyperproliferation and multiple pre- and post-β-selection intrathymic developmental defects. Consistent with deregulated Wnt signaling, TMEM131L-deficient thymocytes expressed Wnt target genes at abnormally high levels, and they displayed both constitutive phosphorylation of Wnt coreceptor LRP6 and β-catenin intranuclear accumulation. Using T cell factor reporter assays, we found that membrane-associated TMEM131L inhibited canonical Wnt/β-catenin signaling at the LRP6 coreceptor level. Whereas membrane-associated TMEM131L did not affect LRP6 expression under basal conditions, it triggered lysosome-dependent degradation of its active phosphorylated form following Wnt activation. Genetic mapping showed that phosphorylated LRP6 degradation did not depend on TMEM131L cytoplasmic part but rather on a conserved extracellular domain proximal to the membrane. Collectively, these data indicate that, during thymopoiesis, stage-specific surface translocation of TMEM131L may regulate immature single-positive thymocyte proliferation arrest by acting through mixed Wnt-dependent and -independent mechanisms.

SIAH ubiquitin ligases target the nonreceptor tyrosine kinase ACK1 for ubiquitinylation and proteasomal degradation

Activated Cdc42-associated kinase 1 (ACK1) is a nonreceptor tyrosine kinase linked to cellular transformation. The aberrant regulation of ACK1 promotes tumor progression and metastasis. Therefore, ACK1 is regarded as a valid target in cancer therapy. Seven in absentia homolog (SIAH) ubiquitin ligases facilitate substrate ubiquitinylation that targets proteins to the proteasomal degradation pathway. Here we report that ACK1 and SIAH1 from Homo sapiens interact in a yeast two-hybrid screen. Protein-protein interaction studies and protein degradation analyses using deletion and point mutants of ACK1 verify that SIAH1 and the related SIAH2 interact with ACK1. The association between SIAHs and ACK1 depends on the integrity of a highly conserved SIAH-binding motif located in the far C-terminus of ACK1. Furthermore, we demonstrate that the interaction of ACK1 with SIAH1 and the induction of proteasomal degradation of ACK1 by SIAH1 are independent of ACK1's kinase activity. Chemical inhibitors blocking proteasomal activity corroborate that SIAH1 and SIAH2 destabilize the ACK1 protein by inducing its proteasomal turnover. This mechanism apparently differs from the lysosomal pathway targeting ACK1 after stimulation with the epidermal growth factor. Our data also show that ACK1, but not ACK1 mutants lacking the SIAH binding motif, has a discernable negative effect on SIAH levels. Additionally, knockdown approaches targeting the SIAH2 mRNA uncover specifically that the induction of SIAH2 expression, by hormonally-induced estrogen receptor (ER) activation, decreases the levels of ACK1 in luminal human breast cancer cells. Collectively, our data provide novel insights into the molecular mechanisms modulating ACK1 and they position SIAH ubiquitin ligases as negative regulators of ACK1 in transformed cells.

SIAH proteins: critical roles in leukemogenesis

The delicate balance between the synthesis and the degradation of proteins ensures cellular homeostasis. Proteases act in an irreversible manner and therefore have to be strictly regulated. The ubiquitin-proteasome system (UPS) is a major pathway for the proteolytic degradation of cellular proteins. As dysregulation of the UPS is observed in most cancers including leukemia, the UPS is a valid target for therapeutic intervention strategies. Ubiquitin-ligases selectively bind substrates to target them for poly-ubiquitinylation and proteasomal degradation. Therefore, pharmacological modulation of these proteins could allow a specific level of control. Increasing evidence accumulates that ubiquitin-ligases termed mammalian seven in absentia homologs (SIAHs) are not only critical for the pathogenesis of solid tumors but also for leukemogenesis. However, the relevance and therapeutic potential of SIAH-dependent processes has not been fully elucidated. Here, we summarize functions of SIAH ubiquitin-ligases in leukemias, how they select leukemia-relevant substrates for proteasomal degradation, and how the expression and activity of SIAH1 and SIAH2 can be modulated in vivo. We also discuss that epigenetic drugs belonging to the group of histone deacetylase inhibitors induce SIAH-dependent proteasomal degradation to accelerate the turnover of leukemogenic proteins. In addition, our review highlights potential areas for future research on SIAH proteins.

Snf1-related kinase inhibits colon cancer cell proliferation through calcyclin-binding protein-dependent reduction of β-catenin

Sucrose nonfermenting 1 (Snf1)-related kinase (SNRK) is a serine/threonine kinase with sequence similarity to AMP-activated protein kinase (AMPK); however, its function is not well characterized. We conducted a gene array to determine which genes are regulated by SNRK. The array demonstrated that SNRK overexpression increased the levels of genes involved in cell proliferation, including calcyclin-binding protein (CacyBP), a member of the ubiquitin ligase complex that targets nonphosphorylated β-catenin for degradation. We confirmed that SNRK increased CacyBP mRNA and protein, and decreased β-catenin protein in HCT116 and RKO colon cancer cells. Furthermore, SNRK inhibited colon cancer cell proliferation, and CacyBP down-regulation reversed the SNRK-mediated decrease in proliferation and β-catenin. SNRK overexpression also decreased β-catenin nuclear localization and target gene transcription, and β-catenin down-regulation reversed the effects of SNRK knockdown on proliferation. SNRK transcript levels were reduced in human colon tumors compared to normal tissue by 35.82%, and stable knockdown of SNRK increased colon cancer cell tumorigenicity. Our results demonstrate that SNRK is down-regulated in colon cancer and inhibits colon cancer cell proliferation through CacyBP up-regulation and β-catenin degradation, resulting in reduced proliferation signaling. These findings reveal a novel function for SNRK in the regulation of colon cancer cell proliferation and β-catenin signaling.

Deletion of Siah-interacting protein gene in Drosophila causes cardiomyopathy

Drosophila is a useful model organism in which the genetics of human diseases, including recent advances in identification of the genetics of heart development and disease in the fly, can be studied. To identify novel genes that cause cardiomyopathy, we performed a deficiency screen in adult Drosophila. Using optical coherence tomography to phenotype cardiac function in awake adult Drosophila, we identified Df(1)Exel6240 as having cardiomyopathy. Using a number of strategies including customized smaller deletions, screening of mutant alleles, and transgenic rescue, we identified CG3226 as the causative gene for this deficiency. CG3226 is an uncharacterized gene in Drosophila possessing homology to the mammalian Siah-interacting protein (SIP) gene. Mammalian SIP functions as an adaptor protein involved in one of the β-catenin degradation complexes. To investigate the effects of altering β-catenin/Armadillo signaling in the adult fly, we measured heart function in flies expressing either constitutively active Armadillo or transgenic constructs that block Armadillo signaling, specifically in the heart. While, increasing Armadillo signaling in the heart did not have an effect on adult heart function, decreasing Armadillo signaling in the fly heart caused the significant reduction in heart chamber size. In summary, we show that deletion of CG3226, which has homology to mammalian SIP, causes cardiomyopathy in adult Drosophila. Alterations in Armadillo signaling during development lead to important changes in the size and function of the adult heart.

S100A6 protein negatively regulates CacyBP/SIP-mediated inhibition of gastric cancer cell proliferation and tumorigenesis

Calcyclin-binding protein (CacyBP/SIP), identified on the basis of its ability to interact with S100 proteins in a calcium-dependent manner, was previously found to inhibit the proliferation and tumorigenesis of gastric cancer cells in our laboratory. Importantly, the effects of S100 proteins on the biological behavior of CacyBP/SIP in gastric cancer remain unclear. Herein, we report the construction of eukaryotic expression vectors for wild-type CacyBP/SIP and a truncated mutant lacking the S100 protein binding domain (CacyBP/SIPΔS100). The expressions of the wild-type and truncated recombinant proteins were demonstrated by transfection of MKN45 gastric cancer cells. Co-immunoprecipitation assays demonstrated interaction between S100A6 and wild-type CacyBP/SIP in MKN45 cells. Removal of the S100 protein binding domain dramatically reduced the affinity of CacyBP/SIP for S100 proteins as indicated by reduced co-immunoprecipitation of S100A6 by CacyBP/SIPΔS100. The MTT assay, FACS assay, clonogenic assay and tumor xenograft experiment were performed to assess the effect of CacyBP/SIP on cell growth and tumorigenesis in vitro and in vivo. Overexpression of CacyBP/SIP inhibited the proliferation and tumorigenesis of MKN45 gastric cancer cells; the proliferation and tumorigenesis rates were even further reduced by the expression of CacyBP/SIPΔS100. We also showed that S100 proteins negatively regulate CacyBP/SIP-mediated inhibition of gastric cancer cell proliferation, through an effect on β-catenin protein expression and transcriptional activation of Tcf/LEF. Although the underlying mechanism of action requires further investigation, this study provides new insight into the interaction between S100 proteins and CacyBP/SIP, which might enrich our knowledge of S100 proteins and be helpful for our understanding of the development of gastric cancer.

Siah1/SIP regulates p27(kip1) stability and cell migration under metabolic stress

p27(kip1) has been implicated in cell cycle regulation, functioning as an inhibitor of cyclin-dependent kinase activity. In addition, p27 was also shown to affect cell migration, with accumulation of cytoplasmic p27 associated with tumor invasiveness. However, the mechanism underlying p27 regulation as a cytoplasmic protein is poorly understood. Here we show that glucose starvation induces proteasome-dependent degradation of cytoplasmic p27, accompanied by a decrease in cell motility. We also show that the glucose limitation-induced p27 degradation is regulated through an ubiquitin E3 ligase complex involving Siah1 and SIP/CacyBP. SIP (-/-) embryonic fibroblasts have increased levels of cytosolic p27 and exhibit increased cell motility compared to wild-type cells. These observations suggest that the Siah1/SIP E3 ligase complex regulates cell motility through degradation of p27.

Relationship between CacyBP/SIP expression and prognosis in astrocytoma

The aim of this study was to investigate the expression of calcyclin-binding protein (also known as Siah-1-interacting protein [CacyBP/SIP]) in astrocytoma and to determine its prognostic value in overall survival of patients with glioblastoma multiforme (GBM). Tissue specimens were obtained from 77 Chinese patients who had undergone surgery for astrocytoma. The expression of CacyBP/SIP was examined by immunohistochemistry. The relationship between CacyBP/SIP and proliferating cell nuclear antigen index (PCNA) expression was investigated, and the prognostic value of CacyBP/SIP expression in patients with astrocytomas was analyzed. Of 77 tumors, 49 (63.6%) were negative for CacyBP/SIP expression. Loss of CacyBP/SIP expression was significantly associated with a high histological grade and with poor survival in univariate and multivariate analyses. Cox multivariable analysis showed that loss of CacyBP/SIP expression correlated with poor prognosis in patients with astrocytomas and was an independent prognostic factor (p<0.05). The mean survival time of patients with tumors that had lost expression of CacyBP/SIP was 25.58months (95% confidence interval [CI], 15.36-25.81months), compared to a mean survival time of 36.37months (95% CI, 27.90-44.84months) for patients with CacyBP/SIP-expressing tumors. CacyBP/SIP expression was also negatively correlated with PCNA expression in astrocytoma tissue (p<0.05). Our findings suggest that CacyBP/SIP may have an important role as a negative regulator of astrocytoma development and progression, and that CacyBP/SIP might be a useful molecular marker for predicting the prognosis of astrocytoma.

A distinct role of CD4+ Th17- and Th17-stimulated CD8+ CTL in the pathogenesis of type 1 diabetes and experimental autoimmune encephalomyelitis

Both CD4(+) Th17-cells and CD8(+) cytotoxic T lymphocytes (CTLs) are involved in type 1 diabetes and experimental autoimmune encephalomyelitis (EAE). However, their relationship in pathogenesis of these autoimmune diseases is still elusive. We generated ovalbumin (OVA)- or myelin oligodendrocyte glycoprotein (MOG)-specific Th17 cells expressing RORγt and IL-17 by in vitro co-culturing OVA-pulsed and MOG(35-55) peptide-pulsed dendritic cells (DC(OVA) and DC(MOG)) with CD4(+) T cells derived from transgenic OTII and MOG-T cell receptor mice, respectively. We found that these Th17 cells when transferred into C57BL/6 mice stimulated OVA- and MOG-specific CTL responses, respectively. To assess the above question, we adoptively transferred OVA-specific Th17 cells into transgenic rat insulin promoter (RIP)-mOVA mice or RIP-mOVA mice treated with anti-CD8 antibody to deplete Th17-stimulated CD8(+) T cells. We demonstrated that OVA-specific Th17-stimulated CTLs, but not Th17 cells themselves, induced diabetes in RIP-mOVA. We also transferred MOG-specific Th17 cells into C57BL/6 mice and H-2K(b-/-) mice lacking of the ability to generate Th17-stimulated CTLs. We further found that MOG-specific Th17 cells, but not Th17-activated CTLs induced EAE in C57BL/6 mice. Taken together, our data indicate a distinct role of Th17 cells and Th17-stimulated CTLs in the pathogenesis of TID and EAE, which may have great impact on the overall understanding of Th17 cells in the pathogenesis of autoimmune diseases.

CacyBP/SIP expression is involved in the clinical progression of breast cancer

OBJECTIVE

Calcyclin-binding protein or Siah-1-interacting protein (CacyBP/SIP) is a target protein of the S100A6, which is a member of the S100 family. It has been shown that CacyBP/SIP plays important roles in cell cycle progression, differentiation, and carcinogenesis. The purpose of this study was to explore the correlation of CacyBP/SIP expression and clinical significance in breast cancer.

METHODS

Immunohistochemistry was performed to detect the CacyBP/SIP expression in 79 pairs of breast cancer tissues and adjacent nontumor tissues. Western blot analysis and semiquantitative RT-PCR were used to measure CacyBP/SIP protein and mRNA levels in three pairs of fresh breast cancer tissues and adjacent nontumor tissues. The clinical data were collected by telephone follow-up for 5 years.

RESULTS

CacyBP/SIP mRNA and protein levels in breast cancer tissues were significantly higher compared with adjacent nontumor tissues. Poor cellular differentiation, lymph node invasion, and clinicopathological staging in breast cancer were associated with CacyBP/SIP expression. Other factors, such as age, menses, and tumor size, were not related to CacyBP/SIP expression. The up-regulation of CacyBP/SIP expression also was shown to increase recurrence and metastasis of breast cancer and to correlate with short overall survival rate.

CONCLUSIONS

CacyBP/SIP expression is evident in more advanced clinical progression of breast cancer, and it might be a biomarker for poor prognosis and a potential therapeutic target in breast cancer.

ID3 mediates X-ray-induced apoptosis of keratinocytes through the regulation of β-catenin

BACKGROUND

Ionizing radiation is used to treat many of cancers, however, it also produces unwanted side effect on normal tissues, such as radiodermatitis. We previously established an animal model for radiodermatitis, and found that X-ray irradiation induced the expression of ID3 in hairless mouse skin by cDNA microarray.

OBJECTIVE

The aim of this study is to investigate the functional role of ID3 in X-ray irradiated keratinocytes.

METHODS

Immunohistochemistry, RT-PCR and Western blot were performed to demonstrate the ID3 induction by X-ray irradiation. HaCaT keratinocytes were transduced with the recombinant adenovirus expressing HA-ID3, and then effects on apoptosis were analyzed.

RESULTS

X-ray irradiation increased markedly the ID3 protein level in epidermis of mouse skin. X-ray irradiation also induced the expression of ID3 in HaCaT keratinocytes cultured in vitro, at both mRNA and protein levels. When ID3 was overexpressed by recombinant adenovirus, apoptosis of keratinocytes were induced even in the absence of X-ray irradiation. Furthermore, overexpression of ID3 sensitized X-ray-induced apoptosis. Interestingly, X-ray irradiation significantly reduced the endogenous β-catenin level, which was related with induction of apoptosis. Similarly, overexpression of ID3 led to remarkable reduction in β-catenin level.

CONCLUSION

These results suggest that ID3 plays a role as an apoptosis inducer in response to X-ray irradiation via the regulation of endogenous β-catenin level.

S100A6 binding protein and Siah-1 interacting protein (CacyBP/SIP): spotlight on properties and cellular function

The CacyBP/SIP protein (S100A6 binding protein and Siah-1 interacting protein) was originally discovered in Ehrlich ascites tumor cells as a S100A6 (calcyclin) target (Filipek and Wojda in Biochem J 320:585-587, 1996; Filipek and Kuźnicki in J Neurochem 70(5):1793-1798, 1998) and later on as a Siah-1 interacting protein (Matsuzawa and Reed in Mol Cell 7(5):915-926, 2001). CacyBP/SIP binds several target proteins such as some calcium binding proteins of the S100 family (Filipek et al. in J Biol Chem 277(32):28848-28852, 2002), Skp1 (Matsuzawa and Reed in Mol Cell 7(5):915-926, 2001), tubulin (Schneider et al. in Biochim Biophys Acta 1773(11):1628-1636, 2007) and ERK1/2 (Kilanczyk et al. in Biochem Biophys Res Commun 380:54-59, 2009). Studies concerning distribution of CacyBP/SIP show that it is present in various tissues and that a particularly high level of CacyBP/SIP is observed in brain (Jastrzebska et al. in J Histochem Cytochem 48(9):1195-1202, 2000). Regarding the function of CacyBP/SIP, there are some reports suggesting its role in cellular processes such as ubiquitination, proliferation, differentiation, tumorigenesis, cytoskeletal rearrangement or regulation of transcription. This review describes the properties of CacyBP/SIP and summarizes all findings concerning its cellular function.

Dll1 haploinsufficiency in adult mice leads to a complex phenotype affecting metabolic and immunological processes

BACKGROUND

The Notch signaling pathway is an evolutionary conserved signal transduction pathway involved in embryonic patterning and regulation of cell fates during development and self-renewal. Recent studies have demonstrated that this pathway is integral to a complex system of interactions, involving as well other signal transduction pathways, and implicated in distinct human diseases. Delta-like 1 (Dll1) is one of the known ligands of the Notch receptors. The role of the Notch ligands is less well understood. Loss-of-function of Dll1 leads to embryonic lethality, but reduction of Delta-like 1 protein levels has not been studied in adult stage.

METHODOLOGY/PRINCIPAL FINDINGS

Here we present the haploinsufficient phenotype of Dll1 and a missense mutant Dll1 allele (Dll1(C413Y)). Haploinsufficiency leads to a complex phenotype with several biological processes altered. These alterations reveal the importance of Dll1 mainly in metabolism, energy balance and in immunology. The animals are smaller, lighter, with altered fat to lean ratio and have increased blood pressure and a slight bradycardia. The animals have reduced cholesterol and triglyceride levels in blood. At the immunological level a subtle phenotype is observed due to the effect and fine-tuning of the signaling network at the different levels of differentiation, proliferation and function of lymphocytes. Moreover, the importance of the proteolytic regulation of the Notch signaling network emphasized.

CONCLUSIONS/SIGNIFICANCE

In conclusion, slight alterations in one player of Notch signaling alter the entire organism, emphasizing the fine-tuning character of this pathway in a high number of processes.

Sustained expression of pre-TCR induced beta-catenin in post-beta-selection thymocytes blocks T cell development

Pre-TCR and IL-7R signals regulate beta-selection of thymocytes and then must be down-regulated for further development. However, the molecular events that control down-regulation remain unknown. We and others have previously shown that beta-catenin in cooperation with TCF regulates beta-selection. In this paper, we demonstrate that beta-catenin expression is stringently regulated by intrathymic signals, it is expressed at the highest levels in the pre-TCR signaled thymocytes, and is down-regulated in post-beta-selection thymocytes. Pre-TCR-induced beta-catenin regulates initial stages of pre-TCR signaling including expression of early growth response (Egr) genes but must be down-regulated to express RORgammat, which is essential for maturation to the CD4+CD8+ double positive (DP) stage. Sustained expression of beta-catenin results in the generation of IL-7R-, Egr-, and TGFbeta-expressing pre-DP thymocytes that are blocked in development. These data are consistent with a model in which post-beta-selection, pre-TCR-induced beta-catenin expression must return to background levels for efficient transition to the DP stage.

CacyBP/SIP binds ERK1/2 and affects transcriptional activity of Elk-1

In this work we showed for the first time that mouse CacyBP/SIP interacts with extracellular signal regulated kinases 1 and 2 (ERK1/2). We also established that a calcium binding protein, S100A6, competes for this interaction. Moreover, the E217K mutant of CacyBP/SIP does not bind significantly to ERK1/2 although it retains the ability to interact with S100A6. Molecular modeling shows that the E217K mutation in the 189-219 CacyBP/SIP fragment markedly changes its electrostatic potential, suggesting that the binding with ERK1/2 might have an electrostatic character. We also demonstrate that CacyBP/SIP-ERK1/2 interaction inhibits phosphorylation of the Elk-1 transcription factor in vitro and in the nuclear fraction of NB2a cells. Altogether, our data suggest that the binding of CacyBP/SIP with ERK1/2 might regulate Elk-1 phosphorylation/transcriptional activity and that S100A6 might further modulate this effect via Ca(2+)-dependent interaction with CacyBP/SIP and competition with ERK1/2.

Expression and clinical significance of CacyBP/SIP in pancreatic cancer

AIMS

Calcyclin-binding protein or Siah-1-interacting protein (CacyBP/SIP), a component of the ubiquitin-mediated proteolysis, could bind SKP1-CUL1-F box protein complex and participate in beta-catenin degradation, which was found to be related to the malignant phenotypes of gastric cancer and renal cancer. However, the role of CacyBP/SIP in pancreatic cancer progression still remains unclear. Therefore, the aim of the present study was to investigate the expression and clinical significance of CacyBP/SIP in pancreatic cancer.

METHODS

Immunohistochemistry was carried out on paraffin-embedded sections of pancreatic cancer and normal pancreatic tissues. In addition, Western blot and semiquantitative RT-PCR were carried out to analyze mRNA and protein expression of CacyBP/SIP in 8 pairs of freshly resected pancreatic cancer and their adjacent nontumorous tissue.

RESULTS

CacyBP/SIP expression was significantly increased in pancreatic cancer tissue (28/68 or 41.2%) and correlated with differentiation degree, higher TNM (tumor, node, metastasis) stage and distance metastasis. Also, mRNA and protein expression of CacyBP/SIP were found to be at higher levels in almost all cancer tissues compared to adjacent tissues.

CONCLUSIONS

CacyBP/SIP protein might play an important role in the process of pancreatic carcinogenesis and high-level CacyBP/SIP expression might be related to the malignant potential of pancreatic cancer.

Reciprocal negative regulation between S100A7/psoriasin and beta-catenin signaling plays an important role in tumor progression of squamous cell carcinoma of oral cavity

Overexpression of S100A7 (psoriasin), a small calcium-binding protein, has been associated with the development of psoriasis and carcinomas in different types of epithelia, but its precise functions are still unknown. Using human tissue specimens, cultured cell lines, and a mouse model, we found that S100A7 is highly expressed in preinvasive, well-differentiated and early staged human squamous cell carcinoma of the oral cavity (SCCOC), but little or no expression was found in poorly differentiated, later-staged invasive tumors. Interestingly, our results showed that S100A7 inhibits both SCCOC cell proliferation in vitro and tumor growth/invasion in vivo. Furthermore, we demonstrated that S100A7 is associated with the beta-catenin complex, and inhibits beta-catenin signaling by targeting beta-catenin degradation via a noncanonical mechanism that is independent of GSK3beta-mediated phosphorylation. More importantly, our results also indicated that beta-catenin signaling negatively regulates S100A7 expression. Thus, this reciprocal negative regulation between S100A7 and beta-catenin signaling implies their important roles in tumor development and progression. Despite its high levels of expression in early stage SCCOC tumorigenesis, S100A7 actually inhibits SCCOC tumor growth/invasion as well as tumor progression. Downregulation of S100A7 in later stages of tumorigenesis increases beta-catenin signaling, leading to promotion of tumor growth and tumor progression.

Age-dependent changes in neuronal distribution of CacyBP/SIP: comparison to tubulin and the tau protein

CacyBP/SIP was originally identified as an S100A6 (calcyclin) target and later on as a Siah-1 interacting protein. Recently, we have shown that CacyBP/SIP interacts with tubulin, which suggests its involvement in the reorganization of microtubules. In this work we examined the localization of CacyBP/SIP in cultured neurons and in brain neurons of young and aged rats, and compared this localization with that of tubulin and the tau protein. We have found that in neurons of young rats CacyBP/SIP, tubulin and tau are present in the cytoplasm and in the neuronal processes, whereas in aged animals CacyBP/SIP and tau are mainly seen in the cytoplasm of the neuronal somata. In aged rats, these changes are also accompanied by a different localization pattern of tubulin. Thus, our results show that localization of CacyBP/SIP in brain neurons is similar to that observed for tau and tubulin, which points to the involvement of CacyBP/SIP in cytoskeletal physiology.

Calcyclin-binding protein inhibits proliferation, tumorigenicity, and invasion of gastric cancer

Calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP), a target protein of the S100 family, which includes S100A6, S100A1, S100A12, S100B, and S100P, has been identified as a component of a novel ubiquitinylation complex leading to beta-catenin degradation. However, the function of CacyBP/SIP in gastric cancer has not been elucidated. In the present study, we prepared CacyBP/SIP overexpressing and knockdown cell lines of gastric cancer. Forced CacyBP/SIP expression inhibited the proliferation of gastric cancer cells, suppressed tumorigenicity in vitro, and prolonged the survival time of tumor-bearing nude mice. In addition, increased CacyBP/SIP repressed the invasive potential of gastric cancer cells. Conversely, the down-regulation of CacyBP/SIP by RNA interference showed the opposite effects. Further studies showed that depressed CacyBP/SIP increased the expression of total and nuclear beta-catenin at the protein level and elevated the transcriptional activity of Tcf/LEF. Taken together, our results suggest that CacyBP/SIP may be a potential inhibitor of cell growth and invasion in the gastric cancer cell, at least in part through the effect on beta-catenin protein expression and transcriptional activation of Tcf/LEF.

Targeted inactivation of the COP9 signalosome impairs multiple stages of T cell development

Genetic programs promoting cell cycle progression, DNA repair, and survival are coordinately induced in developing T cells and require rapid turnover of effector molecules. As the COP9 signalosome (CSN) has been placed at the crossroads of these programs in lower organisms, we addressed its role by conditionally deleting CSN5/JAB1, its catalytic subunit, in developing thymocytes. CSN5/JAB1^del/del thymocytes show defective S phase progression and massive apoptosis at the double-negative (DN) 4–double-positive (DP) transition stage, which is paralleled by altered turnover of selected CSN-controlled substrates, including p53, IκB-α, and β-catenin. Combined dysregulation of the p53 and NF-κB pathways affects thymocyte survival by altering the mRNA and protein levels of selected Bcl-2 family members. Genetic complementation analysis performed on p53^−/−, Bcl-xL/Bcl-2A1, or T cell receptor transgenic backgrounds indicates that CSN5/JAB1 acts at distinct developmental stages to coordinate proliferation, survival, and positive selection of thymocytes by controlling the induction of defined genetic programs acting downstream of CSN-regulated transcription factors.

The Thymus as an Inductive Site for T Lymphopoiesis

Like all hematopoietic cells, T lymphocytes are derived from bone-marrow-resident stem cells. However, whereas most blood lineages are generated within the marrow, the majority of T cell development occurs in a specialized organ, the thymus. This distinction underscores the unique capacity of the thymic microenvironment to support T lineage restriction and differentiation. Although the identity of many of the contributing thymus-derived signals is well established and rooted in highly conserved pathways involving Notch, morphogenetic, and protein tyrosine kinase signals, the manner in which the ensuing cascades are integrated to orchestrate the underlying processes of T cell development remains under investigation. This review focuses on the current definition of the early stages of T cell lymphopoiesis, with an emphasis on the nature of thymus-derived signals delivered to T cell progenitors that support the commitment and differentiation of T cells toward the alphabeta and gammadelta T cell lineages.

Genomic view of IFN-α response in pre-autoimmune NZB/W and MRL/lpr mice

Interferon (IFN)-alpha is involved in the pathogenesis of systemic lupus erythematosus. Studies in murine lupus models have revealed that type I IFN exerts either a protective effect in MRL/lpr, or can detrimentally impact disease progression, as in NZB/W mice. To understand this paradox, we examined the kinetic global gene expression in pre-autoimmune NZB/W-, MRL/lpr- and normal BALB/c-derived splenic mononuclear cells following ex vivo IFN-alpha treatment. Analysis of IFN-alpha-induced gene expression patterns revealed genes associated with antiproliferative activity of IFN-alpha including CDKN1A, GADD45B, pituitary tumor-transforming 1, SCOTIN, ataxia telangiectasia-mutated homolog and calcyclin-binding protein were upregulated in MRL/lpr and/or BALB/c mice. Of IFN-alpha-induced genes differentially expressed in NZB/W vs BALB/c and MRL/lpr mice at 3 h time point, enhanced expression of CCND1, cyclin D2, matrix metalloproteinase 13 and a panel of cytokines and chemokines and impaired expression of negative inflammatory regulators CD69 and an Src family kinase hemopoietic cell kinase were notable. Interestingly, the splenic mononuclear cells from the NZB/W not MRL/lpr lupus-prone mice at the pre-autoimmune stage before ex vivo IFN-alpha treatment, have increased expression of many known IFN-regulated genes. These results provide a unique genomic view of ex vivo IFN-alpha response in two lupus-prone models, and help to have an insight into the role of IFN-alpha in lupus pathogenesis.

Beta-catenin regulates positive selection of thymocytes but not lineage commitment

Positive selection and lineage commitment to the cytolytic or helper lineage of T cells result in coordinated expression of MHC class I-restricted TCR and CD8 coreceptor or MHC class II-restricted TCR and CD4 molecule. Positive selection signals also regulate the survival and generation of requisite numbers of cytolytic or Th cells. beta-Catenin is the major transcriptional cofactor of T cell factor and plays a role in thymocyte development. In this study, using mice expressing stabilized beta-catenin and mice with T cell-specific deletion of beta-catenin, we show that beta-catenin regulates positive selection, but not lineage commitment of thymocytes. Furthermore, beta-catenin expression accelerates the timing of mature CD8 thymocyte generation such that CD4 and CD8 single-positive thymocytes mature with the same kinetics during development.

β-Catenin (CTNNB1) in the Mouse Uterus During Decidualization and the Potential Role of Two Pathways in Regulating Its Degradation

β-catenin plays a role in cell adhesion and as a transcriptional coactivator. Its levels are regulated in cells by controlling its degradation through ubiquitination by two different E3 ligase complexes. One complex contains β-transducing repeat containing (BTRC) protein, which binds to β-catenin when phosphorylated on specific (S33 and S37) residues, whereas the other involves calcyclin-binding protein (CACYBP). The aim of this study was to determine the localization and levels of total and active (S33/S37-dephosphorylated) β-catenin in the pregnant mouse uteri and those undergoing artificially stimulated decidualization. These two forms of β-catenin were localized almost exclusively to the endometrial epithelia just prior to the onset of implantation. Although this localization continued after the onset of implantation, there were less epithelial cells present in areas of the uterus undergoing decidualization. Rather, there was a progressive increase in β-catenin localization in endometrial stromal cells undergoing decidualization in the anti-mesometrial and, to a lesser extent, in the mesometrial regions. The presence of a conceptus was not required for the changes in localization seen in the pregnant uterus because similar findings were also seen in uteri undergoing artificially stimulated decidualization. Finally, overall levels of total, active (S33 and S37 dephosphorylated), and phosphorylated (S33/S37/T42) β-catenin protein and the steady-state levels of calcyclin-binding protein mRNA changed in the uterus during decidualization. The result of this study shows the changing localization and levels of β-catenin in the mouse uterus during decidualization. Further, the results suggest potential roles for both the BTRC and CACYBP E3 ligase mechanisms of β-catenin ubiquitination in the uterus during decidualization.

Siah-1S, a novel splice variant of Siah-1 (seven in absentia homolog), counteracts Siah-1-mediated downregulation of beta-catenin

Siah-1 (seven in absentia homolog) is known to cause indirect degradation of beta-catenin through formation of a complex with Siah-interacting protein (SIP), Skp1 and Ebi. Here, we report the characterization of a novel splice variant of human Siah-1, designated Siah-1S, which is produced by an alternative splicing mechanism. The novel intron/exon junctions used to generate Siah-1S follow a non-conventional CT-AC rule. Siah-1S exhibits an even shorter half-life than Siah-1 and is able to catalyse self-ubiquitination that results in its subsequent degradation by proteasome. Siah-1S is shown to upregulate beta-catenin-dependent Tcf/Lef transcriptional activation and antagonize Siah-1's potentiation effect on the apoptosis induced by etoposide in MCF-7 cells. Additionally, Siah-1S is found to interact with Siah-1 to form heterodimer or with itself to form homodimer. Unlike homodimer Siah-1*Siah-1, neither Siah-1*Siah-1S nor Siah-1S*Siah-1S is able to bind to Siah-1-interacting protein, which may explain the underlying mechanism for Siah-1S's dominant negative effect on Siah-1. Importantly, results from in vitro soft agar assay demonstrated that Siah-1S displays a promotion effect on cells tumorigenicity.

Ubiquitin-conjugating enzyme Ubc13 is a critical component of TNF receptor-associated factor (TRAF)-mediated inflammatory responses

Ubc13 is a ubiquitin-conjugating enzyme responsible for noncanonical ubiquitination of TNF receptor-associated factor (TRAF)-family adapter proteins involved in Toll-like receptor and TNF-family cytokine receptor signaling, which are regulators of innate immunity. Gene ablation was used to study the function of Ubc13 in mice. Whereas homozygous ubc13 gene disruption resulted in embryonic lethality, heterozygous ubc13(+/-) mice appeared normal, without alterations in immune cell populations. Haploinsufficient ubc13(+/-) mice were resistant to lipopolysaccharide-induced lethality, and demonstrated reduced in vivo ubiquitination of TRAF6. Macrophages and splenocytes isolated from ubc13(+/-) mice exhibited reduced lipopolysaccharide-inducible cytokine secretion and impaired activation of TRAF-dependent signal transduction pathways (NF-kappaB, JNK, and p38 MAPK). These findings document a critical role for Ubc13 in inflammatory responses and suggest that agents reducing Ubc13 activity could have therapeutic utility.

Overexpressed CacyBP/SIP leads to the suppression of growth in renal cell carcinoma

Calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP), a target protein of S100, has been identified as a component of a novel ubiquitinylation complex leading to beta-catenin degradation, which was found to be related to the malignant phenotypes of gastric cancer. However, the roles of CacyBP/SIP in renal cell carcinoma still remain unclear. In the present study, we had analyzed the expression of the CacyBP/SIP protein in human renal cancer cells and clinical tissue samples. The possible roles of CacyBP/SIP in regulating the malignant phenotype of renal cancer cells were also investigated. The results demonstrated that the expression of CacyBP/SIP was markedly down-regulated in renal cell carcinoma tissues and cell lines. Ectopic overexpression of CacyBP/SIP in A498 cells inhibited the proliferation of this cell and delayed cell cycle progression significantly, which might be related to the down-regulation of Cyclin D1 through reducing beta-catenin protein. CacyBP/SIP also suppressed colony formation in soft agar and its tumorigenicity in nude mice. Taken together, our work showed that CacyBP/SIP, as a novel down-regulated gene in renal cell carcinoma, suppressed proliferation and tumorigenesis of renal cancer cells.

Nitric oxide-GAPDH-Siah: a novel cell death cascade

1. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an extremely abundant glycolytic enzyme, and exemplifies the class of proteins with multiple, seemingly unrelated functions. Recent studies indicate that it is a major intracellular messenger mediating apoptotic cell death. This paper reviews the GAPDH cell death cascade and discusses its clinical relevance. 2. A wide range of apoptotic stimuli activate NO formation, which S-nitrosylates GAPDH. The S-nitrosylation abolishes catalytic activity and confers upon GAPDH the ability to bind to Siah, an E3-ubiquitin-ligase, which translocates GAPDH to the nucleus. In the nucleus, GAPDH stabilizes the rapidly turning over Siah, enabling it to degrade selected target proteins and affect apoptosis. 3. The cytotoxicity of mutant Huntingtin (mHtt) requires nuclear translocation which appears to be mediated via a ternary complex of GAPDH-Siah-mHtt. The neuroprotective actions of the monoamine oxidase inhibitor R-(-)-deprenyl (deprenyl) reflect blockade of GAPDH-Siah binding. Thus, novel cytoprotective therapies may emerge from agents that prevent GAPDH-Siah binding.