Mayven induces c-Jun expression and cyclin D1 activation in breast cancer cells

Differently sized drug-loaded mesoporous silica nanoparticles elicit differential gene expression in MCF-7 cancer cells

Aim: This study investigates the effects of different sized unmodified and chemo-responsive mesoporous silica nanocarriers on MCF-7 cancer cells. Materials & methods: Unmodified and thiol-functionalized large and small-sized mesoporous MCM-41 silica nanoparticles prepared using templated sol-gel process were characterized for their physicochemical properties and in vitro and in vivo anticancer efficacy. Microarray analysis was carried out to assess their differential effect on gene expression. Results: Thiol-functionalized nanoparticles displayed chemo responsive release and greater cytotoxicity to cancer cells when compared with unmodified carriers. Microarray studies showed distinct differences in genes differentially regulated by sMCM-41and lMCM-41 carriers when compared with the free drug. Conclusion: The small chemo-responsive carrier was more effective in suppressing oncogenes and genes involved in proliferation, invasion and survival while the large carrier mainly altered membrane-associated pathways.

Deubiquitinase USP28 inhibits ubiquitin ligase KLHL2-mediated uridine-cytidine kinase 1 degradation and confers sensitivity to 5'-azacytidine-resistant human leukemia cells

Resistance to the chemotherapeutic drug 5'-azacytidine (5'-AZA) is a major obstacle in the treatment of patients with acute myeloid leukemia (AML). The uridine-cytidine kinase 1 (UCK1) has an established role in activating 5'-AZA and its protein level is significantly downregulated in patients resistant to the drug. However, the underlying molecular mechanism for the reduced UCK1 expression remains to be elucidated. Methods: Using mass spectrometry and molecular biochemistry analyses, we identified specific enzymes mediating UCK1 degradation. Human AML cell lines and murine AML model were used to characterize the effects of these enzymes on 5'-AZA resistance. Results: We demonstrated that the ubiquitin E3 ligase KLHL2 interacted with UCK1 and mediated its polyubiquitination at the K81 residue and degradation. We showed that deubiquitinase USP28 antagonized KLHL2-mediated polyubiquitylation of UCK1. We also provided evidence that ATM-mediated phosphorylation of USP28 resulted in its disassociation from KLHL2 and UCK1 destabilization. Conversely, UCK1 phosphorylation by 5'-AZA-activated ATM enhanced the KLHL2-UCK1 complex formation. Importantly, silencing KLHL2 or USP28 overexpression not only inhibited AML cell proliferation but also sensitized AML cells to 5'-AZA-induced apoptosis in vitro and in vivo. These results were no longer observed in USP28-deficient cells. Conclusions: Our study revealed a novel mechanism by which the KLHL2/USP28/ATM axis mediates resistance of AML cells to 5'-AZA by regulating UCK1 ubiquitination and phosphorylation. These results have direct clinical implications and provide a rationale for the combination drug treatment of AML patients.

Identification of Novel Breast Cancer Genes based on Gene Expression Profiles and PPI Data

Background:

Breast cancer is one of the most common malignancies, and a threat to female health all over the world. However, the molecular mechanism of breast cancer has not been fully discovered yet.

Objective:

It is crucial to identify breast cancer-related genes, which could provide new biomarker for breast cancer diagnosis as well as potential treatment targets.

Methods:

Here we used the minimum redundancy-maximum relevance (mRMR) method to select significant genes, then mapped the transcripts of the genes on the Protein-Protein Interaction (PPI) network and traced the shortest path between each pair of two proteins.

Results:

As a result, we identified 24 breast cancer-related genes whose betweenness were over 700. The GO enrichment analysis indicated that the transcription and oxygen level are very important in breast cancer. And the pathway analysis indicated that most of these 24 genes are enriched in prostate cancer, endocrine resistance, and pathways in cancer.

Conclusion:

We hope these 24 genes might be useful for diagnosis, prognosis and treatment for breast cancer.

KLHL2 interacts with and ubiquitinates WNK kinases

Mutations in the WNK1 and WNK4 genes result in an inherited hypertensive disease, pseudohypoaldosteronism type II (PHAII). Recently, the KLHL3 and Cullin3 genes were also identified as responsible genes for PHAII. Although we have reported that WNK4 is a substrate for the KLHL3-Cullin3 E3 ligase complex, it is not clear whether all of the WNK isoforms are regulated only by KLHL3. To explore the interaction of WNKs and other Kelch-like proteins, we focused on KLHL2 (Mayven), a human homolog of Drosophila Kelch that shares the highest similarity with KLHL3. We found that KLHL2, as well as KLHL3, was co-immunoprecipitated with all four WNK isoforms. The direct interaction of KLHL2 with WNKs was confirmed on fluorescence correlation spectroscopy. Co-expression of KLHL2 and Cullin3 decreased the abundance of WNK1, WNK3 and WNK4 within HEK293T cells, and a significant increase of WNK4 ubiquitination by KLHL2 and Cullin3 was observed both in HEK293T cells and in an in vitro ubiquitination assay. These results suggest that KLHL2-Cullin3 also functions as an E3-ligase for WNK isoforms within the body.

An evolutionary shift in the regulation of the Hippo pathway between mice and flies

The Hippo pathway plays a key role in controlling organ growth in many animal species and its deregulation is associated with different types of cancer. Understanding the regulation of the Hippo pathway and discovering upstream regulators is thus a major quest. Interestingly, while the core of the Hippo pathway contains a highly conserved kinase cascade, different components have been identified as upstream regulators in Drosophila and vertebrates. However, whether the regulation of the Hippo pathway is indeed different between Drosophila and vertebrates or whether these differences are due to our limited analysis of these components in different organisms is not known. Here we show that the mouse Fat4 cadherin, the ortholog of the Hippo pathway regulator Fat in Drosophila, does not apparently regulate the Hippo pathway in the murine liver. In fact, we uncovered an evolutionary shift in many of the known upstream regulators at the base of the arthropod lineage. In this evolutionary transition, Fat and the adaptor protein Expanded gained novel domains that connected them to the Hippo pathway, whereas the cell-adhesion receptor Echinoid evolved as a new protein. Subsequently, the junctional adaptor protein Angiomotin (Amot) was lost and the downstream effector Yap lost its PDZ-binding motif that interacts with cell junction proteins. We conclude that fundamental differences exist in the upstream regulatory mechanisms of Hippo signaling between Drosophila and vertebrates.

Interaction of an intracellular pentraxin with a BTB-Kelch protein is associated with ubiquitylation, aggregation and neuronal apoptosis

Neuronal pentraxin with chromo domain (NPCD) comprises a group of neuronally expressed pentraxins with both membrane and cytosolic isoforms; the functions of cytosolic NPCD isoforms are not clear. Here, we demonstrate that a cytosolic NPCD isoform selectively interacts with the BTB-Kelch protein Mayven/Kelch-like 2 (KLHL2), an actin-binding protein implicated in process outgrowth in oligodendrocytes. The KLHL2-NPCD interaction was identified by a yeast two-hybrid screen and confirmed through colocalization and co-immunoprecipitation studies. Truncation analysis indicates that the Kelch domains of KLHL2 interact with the pentraxin domain of NPCD. NPCD forms protein inclusion bodies (aggresomes) when overexpressed in tissue culture cells, KLHL2 localizes to these aggresomes, and overexpression of KLHL2 increases NPCD aggresome formation. Since other members of the BTB-Kelch family can act as Cullin-RING type E3 ubiquitin ligases, we tested the potential role of KLHL2 as a ubiquitin ligase for NPCD. We found that KLHL2 interacts selectively with Cullin 3, a key component of BTB-Kelch ubiquitin ligase complexes. Further, overexpression of KLHL2 promotes NPCD ubiquitylation. Together, these results suggest a novel E3 ubiquitin ligase function of KLHL2, with NPCD as a substrate. As the formation of aggresomes is often associated with protein aggregation in neurodegenerative diseases, we tested the effects of NPCD overexpression and KLHL2 coexpression on neuronal viability. Overexpression of NPCD in hippocampal neurons led to cell death and apoptosis; this effect was exacerbated by KLHL2 co-expression. Our findings implicate KLHL2 in ubiquitin ligase activity, and suggest potential roles of NPCD and KLHL2 in neurodegeneration.

Subcellular localization of Mayven following expression of wild type and mutant EGFP tagged cDNAs

BACKGROUND

Process formation by glial cells is crucial to their function. Mayven, an actin binding, multi-domain polypeptide, and member of the BTB-BACK-Kelch family have been shown to be important in oligodendrocyte process extension. To assess the role of Mayven in neural cell process extension we have tracked the subcellular distribution of exogenous Mayven following expression of a rat Mayven -EGFP cDNA in a variety of neural cell backgrounds and specifically in OEC tranfectants following drug treatment to disrupt the integrity of the cytoskeleton. A comparison was made between the subcellular localization following transient transfection of OECs with full-length Mayven cDNA and a series of mutant domain constructs.

RESULTS

The subcellular location of Mayven in OEC transfectants showed a characteristic distribution with intense foci of staining towards the process tips corresponding to regions of accumulated Mayven overlapping in part with lammelipodial actin and was absent from the filipodia and the outer membrane. This signature pattern was also observed in Schwann cells, Oli-Neu cells, astrocytes and the neuroblastoma cell line B104 transfectants and resembled the exogenous and endogenous Mayven distribution in oligodendrocytes. This contrasted with the localization pattern in non-neural cells. There was a re-localization of Mayven in OEC transfectants following drug treatment to challenge the integrity of the actin cytoskeleton while breakdown of the microtubular component had no discernible impact on the accumulation of Mayven in the process tips. Deletion of the first three amino acids of the SH3 motif of the putative Fyn Kinase binding domain at the amino terminus significantly compromised this signature pattern as did the removal of the last Kelch repeat unit of six unit Kelch domain comprising the carboxyl terminus. In addition, there was a reduction in process length in mutant transfectants. Co-expression studies with a haemagglutinin (HA) tagged wild type Mayven cDNA and EGFP tagged mutant cDNAs suggested a homomeric interaction mediated by the BTB/POZ domain.

CONCLUSIONS

Exogenous Mayven is transported to the lamellipodia in neural transfectants associating with the actin cytoskeletal network. In addition to the importance of the internal BTB/POZ domain, this subcellular distribution pattern is dependent on the presence of an intact amino and carboxyl terminus.

Rho GTPases of the RhoBTB subfamily and tumorigenesis

RhoBTB proteins constitute a subfamily of atypical members within the Rho family of small guanosine triphosphatases (GTPases). Their most salient feature is their domain architecture: a GTPase domain (in most cases, non-functional) is followed by a prolinerich region, a tandem of 2 broadcomplex, tramtrack, bric a brac (BTB) domains, and a conserved Cterminal region. In humans, the RhoBTB subfamily consists of 3 isoforms: RhoBTB1, RhoBTB2, and RhoBTB3. Orthologs are present in several other eukaryotes, such as Drosophila and Dictyostelium, but have been lost in plants and fungi. Interest in RhoBTB arose when RHOBTB2 was identified as the gene homozygously deleted in breast cancer samples and was proposed as a candidate tumor suppressor gene, a property that has been extended to RHOBTB1. The functions of RhoBTB proteins have not been defined yet, but may be related to the roles of BTB domains in the recruitment of cullin3, a component of a family of ubiquitin ligases. A model emerges in which RhoBTB proteins are required to maintain constant levels of putative substrates involved in cell cycle regulation or vesicle transport through targeting for degradation in the 26S proteasome. RhoBTB proteins are engrossing the list of Rho GTPases involved in tumorigenesis. Unlike typical Rho GTPases (usually overexpressed or hyperactive), RhoBTB proteins appear to play a part in the carcinogenic process through a mechanism that involves the decreased or abolished expression of the corresponding genes, or more rarely, mutations that result in impaired functioning of the protein, presumably leading to the accumulation of RhoBTB substrates and alterations of the cellular homeostasis.

The AP-1 transcription factor regulates breast cancer cell growth via cyclins and E2F factors

The activating protein-1 (AP-1) transcription factor transduces growth signals through signal transduction pathways to the nucleus, leading to the expression of genes involved in growth and malignant transformation in many cell types. We have previously shown that overexpression of a dominant negative form of the cJun proto-oncogene, a cJun dominant negative mutant (Tam67), blocks AP-1 transcriptional activity, induces a G(1) cell cycle block and inhibits breast cancer cell growth in vitro and in vivo. We found that AP-1 blockade by Tam67 in MCF-7 breast cancer cells downregulates cyclin D1 transcriptional activity by at least two mechanisms: by suppressing transcription at the known AP-1 binding site (-934/-928) and by suppressing growth factor-induced expression through suppressing E2F activation at the E2F-responsive site (-726/-719). AP-1 blockade also led to reduced expression of E2F1 and E2F2, but not E2F4, at the mRNA and protein levels. Chromatin immunoprecipitation and supershift assays demonstrated that AP-1 blockade caused decreased binding of E2F1 protein to the E2F site in the cyclin D1 promoter. We also found that Tam67 suppressed the expression of the E2F1 dimerizing partner, DP1 and E2F-upregulated cell cycle genes (cyclins E, A, B and D3) and enhanced the expression of E2F-downregulated cell cycle genes (cyclins G(2) and I). Reduced expression of other E2F-regulated genes was also seen with AP-1 blockade and E2F suppression. Thus, the AP-1 factor regulates the expression of cyclin D and E2F (the latter in turn regulates E2F-downstream genes), leading to cell cycle progression and breast cancer cell proliferation.

Mapping a Sex Hormone–Sensitive Gene Determining Female Resistance to Liver Carcinogenesis in a Congenic F344.BN-Hcs4Rat

Hepatocellular carcinoma (HCC) is prevalent in human and rodent males. Hepatocarcinogenesis is controlled by various genes in susceptible F344 and resistant Brown Norway (BN) rats. B alleles at Hcs4 locus, on RNO16, control neoplastic nodule volume. We constructed the F344.BN-Hcs4 recombinant congenic strain (RCS) by introgressing a 4.41-cM portion of Hcs4 from BN strain in an isogenic F344 background. Preneoplastic and neoplastic lesions were induced by the "resistant hepatocyte" protocol. Eight weeks after initiation, lesion volume and positivity for proliferating cell nuclear antigen (PCNA) were much higher in lesions of F344 than BN rats of both sexes. These variables were lower in females than in males. Lesion volume and PCNA values of male RCS were similar to those of F344 rats, but in females corresponded to those of BN females. Carcinomatous nodules and HCC developed at 32 and 60 weeks, respectively, in male F344 and congenics and, rarely, in F344 females. BN and congenic females developed only eosinophilic/clear cells nodules. Gonadectomy of congenic males, followed by beta-estradiol administration, caused a decrease in Ar expression, an increase in Er-alpha expression, and development of preneoplastic lesions comparable to those from BN females. Administration of testosterone to gonadectomized females led to Ar increase and development of preneoplastic lesions as in F344 males. This indicates a role of homozygous B alleles at Hcs4 in the determination of phenotypic patterns of female RCS and presence at Hcs4 locus of a high penetrance gene(s), activated by estrogens and inhibited/unaffected by testosterone, conferring resistance to females in which the B alleles provide higher resistance.

Detection of Autoantibodies to the BTB-kelch Protein KLHL7 in Cancer Sera

The aim of the study was to search for novel targets of autoantibodies in patients with paraneoplastic neurological syndromes (PNS). PNS are mediated by immune reactions against autoantigen(s) shared by the cancer cells and the nervous system. By serological screening of a rat cerebellum cDNA expression library using anti-Hu-positive sera from three patients with paraneoplastic encephalomyelitis (PEM), we identified an open reading frame encoding an isoform of the BTB-kelch protein KLHL7. Immunohistochemical studies demonstrated that the KLHL7 protein is expressed in the nuclei of neurones, but not in other tissues including various cancers. However, the KLHL7 protein was detected in the nuclei of cancer cell lines. Antibodies to KLHL7 were detected by an immunoprecipitation assay in sera from 12 of 254 (4.7%) patients with various cancers and 2 of 170 blood donors (1.2%). None of 50 sera from patients with multiple sclerosis were positive for KLHL7 antibodies. Sixteen patients with classical PNS and anti-Hu or anti-Yo antibodies were also negative for KLHL7 antibodies. Seven cancer patients with KLHL7 antibodies had various signs of neurological disease that could be related to cancer, whereas the remaining five seropositive cancer patients had no clinical signs of possible PNS. The present results indicate that KLHL7 antibodies are associated with various cancers, and in some patients also with neurological disease. Whether KLHL7 antibodies can be used as paraneoplastic markers for PNS remains to be determined.