Rabring7 degrades c-Myc through complex formation with MM-1

E3 ubiquitin ligase BCA2 promotes breast cancer stemness by up-regulation of SOX9 by LPS

Triple-negative breast cancer (TNBC) is the most malignant subtype of breast cancer. Breast cancer stem cells (BCSCs) are believed to play a crucial role in the carcinogenesis, therapy resistance, and metastasis of TNBC. It is well known that inflammation promotes stemness. Several studies have identified breast cancer-associated gene 2 (BCA2) as a potential risk factor for breast cancer incidence and prognosis. However, whether and how BCA2 promotes BCSCs has not been elucidated. Here, we demonstrated that BCA2 specifically promotes lipopolysaccharide (LPS)-induced BCSCs through LPS induced SOX9 expression. BCA2 enhances the interaction between myeloid differentiation primary response protein 88 (MyD88) and Toll-like receptor 4 (TLR4) and inhibits the interaction of MyD88 with deubiquitinase OTUD4 in the LPS-mediated NF-κB signaling pathway. And SOX9, an NF-κB target gene, mediates BCA2's pro-stemness function in TNBC. Our findings provide new insights into the molecular mechanisms by which BCA2 promotes breast cancer and potential therapeutic targets for the treatment of breast cancer.

PFDN4 as a Prognostic Marker Was Associated with Chemotherapy Resistance through CREBP1/AURKA Pathway in Triple-Negative Breast Cancer

Breast cancer is the most common malignancy and its incidence is increasing. It is currently mainly treated by clinical chemotherapy, but chemoresistance remains poorly understood. Prefolded proteins 4 (PFDN4) are molecular chaperone complexes that bind to newly synthesized polypeptides and allow them to fold correctly to stabilize protein formation. This study aimed to investigate the role of PFDN4 in chemotherapy resistance in breast cancer. Our study found that PFDN4 was highly expressed in breast cancer compared to normal tissues and was statistically significantly associated with stage, nodal status, subclasses (luminal, HER2 positive and triple negative), triple-negative subtype and disease-specific survival by TCGA database analysis. CRISPR knockout of PFDN4 inhibited the growth of 89% of breast cancer cell lines, and the triple-negative cell line exhibited a stronger inhibitory effect than the non-triple-negative cell line. High PFDN4 expression was associated with poor overall survival in chemotherapy and resistance to doxorubicin and paclitaxel through the CREBP1/AURKA pathway in the triple-negative MDAMB231 cell line. This study provides insightful evidence for the value of PFDN4 in poor prognosis and chemotherapy resistance in breast cancer patients.

Cancer-Associated Dysregulation of Sumo Regulators: Proteases and Ligases

SUMOylation is a post-translational modification that has emerged in recent decades as a mechanism involved in controlling diverse physiological processes and that is essential in vertebrates. The SUMO pathway is regulated by several enzymes, proteases and ligases being the main actors involved in the control of sumoylation of specific targets. Dysregulation of the expression, localization and function of these enzymes produces physiological changes that can lead to the appearance of different types of cancer, depending on the enzymes and target proteins involved. Among the most studied proteases and ligases, those of the SENP and PIAS families stand out, respectively. While the proteases involved in this pathway have specific SUMO activity, the ligases may have additional functions unrelated to sumoylation, which makes it more difficult to study their SUMO-associated role in cancer process. In this review we update the knowledge and advances in relation to the impact of dysregulation of SUMO proteases and ligases in cancer initiation and progression.

Multifaceted Roles of the E3 Ubiquitin Ligase RING Finger Protein 115 in Immunity and Diseases

Ubiquitination is a post-translational modification that plays essential roles in various physiological and pathological processes. Protein ubiquitination depends on E3 ubiquitin ligases that catalyze the conjugation of ubiquitin molecules on lysine residues of targeted substrates. RING finger protein 115 (RNF115), also known as breast cancer associated gene 2 (BCA2) and Rab7-interacting RING finger protein (Rabring7), has been identified as a highly expressed protein in breast cancer cells and tissues. Later, it has been demonstrated that RNF115 catalyzes ubiquitination of a series of proteins to modulate a number of signaling pathways, and thereby regulates viral infections, autoimmunity, cell proliferation and death and tumorigenesis. In this review, we introduce the identification, expression and activity regulation of RNF115, summarize the substrates and functions of RNF115 in different pathways, and discuss the roles of RNF115 as a biomarker or therapeutic target in diseases.

Prefoldin Function in Cellular Protein Homeostasis and Human Diseases

Cellular functions are largely performed by proteins. Defects in the production, folding, or removal of proteins from the cell lead to perturbations in cellular functions that can result in pathological conditions for the organism. In cells, molecular chaperones are part of a network of surveillance mechanisms that maintains a functional proteome. Chaperones are involved in the folding of newly synthesized polypeptides and assist in refolding misfolded proteins and guiding proteins for degradation. The present review focuses on the molecular co-chaperone prefoldin. Its canonical function in eukaryotes involves the transfer of newly synthesized polypeptides of cytoskeletal proteins to the tailless complex polypeptide 1 ring complex (TRiC/CCT) chaperonin which assists folding of the polypeptide chain in an energy-dependent manner. The canonical function of prefoldin is well established, but recent research suggests its broader function in the maintenance of protein homeostasis under physiological and pathological conditions. Interestingly, non-canonical functions were identified for the prefoldin complex and also for its individual subunits. We discuss the latest findings on the prefoldin complex and its subunits in the regulation of transcription and proteasome-dependent protein degradation and its role in neurological diseases, cancer, viral infections and rare anomalies.

Influence of prefoldin subunit 4 on the tolerance of Kluyveromyces marxianus to lignocellulosic biomass-derived inhibitors

BACKGROUND

Kluyveromyces marxianus is a potentially excellent host for microbial cell factories using lignocellulosic biomass, due to its thermotolerance, high growth rate, and wide substrate spectrum. However, its tolerance to inhibitors derived from lignocellulosic biomass pretreatment needs to be improved. The prefoldin complex assists the folding of cytoskeleton which relates to the stress tolerance, moreover, several subunits of prefoldin have been verified to be involved in gene expression regulation. With the presence of inhibitors, the expression of a gene coding the subunit 4 of prefoldin (KmPFD4), a possible transcription factor, was significantly changed. Therefore, KmPFD4 was selected to evaluate its functions in inhibitors tolerance.

RESULTS

In this study, the disruption of the prefoldin subunit 4 gene (KmPFD4) led to increased concentration of intracellular reactive oxygen species (ROS) and disturbed the assembly of actin and tubulin in the presence of inhibitors, resulting in reduced inhibitor tolerance. Nuclear localization of KmPFD4 indicated that it could regulate gene expression. Transcriptomic analysis showed that upregulated gene expression related to ROS elimination, ATP production, and NAD+ synthesis, which is a response to the presence of inhibitors, disappeared in KmPFD4-disrupted cells. Thus, KmPFD4 impacts inhibitor tolerance by maintaining integration of the cytoskeleton and directly or indirectly affecting the expression of genes in response to inhibitors. Finally, overexpression of KmPFD4 enhanced ethanol fermentation with a 46.27% improvement in productivity in presence of the inhibitors.

CONCLUSION

This study demonstrated that KmPFD4 plays a positive role in the inhibitor tolerance and can be applied for the development of inhibitor-tolerant platform strains.

Effects of the SUMO Ligase BCA2 on Metabolic Activity, Cell Proliferation, Cell Migration, Cell Cycle, and the Regulation of NF-κB and IRF1 in Different Breast Epithelial Cellular Contexts

Breast cancer-associated gene 2 (BCA2) is an E3 ubiquitin and SUMO ligase with antiviral properties against HIV. Specifically, BCA2 (i) enhances the restriction imposed by BST2/Tetherin, impeding viral release; (ii) promotes the ubiquitination and degradation of the HIV protein Gag, limiting virion production; (iii) down-regulates NF-κB, which is necessary for HIV RNA synthesis; and (iv) activates the innate transcription factor IRF1. Due to its antiviral properties, ectopic expression of BCA2 in infected cells represents a promising therapeutic approach against HIV infection. However, BCA2 up-regulation is often observed in breast tumors. To date, the studies about BCA2 and cancer development are controversial, stating both pro- and anti-oncogenic roles. Here, we investigated the impact of BCA2 on cellular metabolic activity, cell proliferation, cell migration, and cell cycle progression. In addition, we also examined the ability of BCA2 to regulate NF-κB and IRF1 in transformed and non-tumor breast epithelial environments. Despite the fact that BCA2 promotes the transition from G1 to S phase of the cell cycle, it did not increase cell proliferation, migration nor metabolic activity. As expected, BCA2 maintains its enzymatic function at inhibiting NF-κB in different breast cancer cell lines. However, the effect of BCA2 on IRF1 differs depending on the cellular context. Specifically, BCA2 activates IRF1 in ER⁺ breast cell lines while it inhibits this transcription factor in ER^– breast cancer cells. We hypothesize that the distinct actions of BCA2 over IRF1 may explain, at least in part, the different proposed roles for BCA2 in these cancers.

Ultraviolet B irradiation up-regulates MM1 and induces photoageing of the epidermis

BACKGROUND

ΔNp63α and c-Myc are key transcription factors controlling proliferation and senescence in epithelial cells. We previously reported that the c-Myc modulator MM1 and its E3 ligase, HERC3, together with the transcription factor ΔNp63α, compose a feedback loop, which regulates proliferative senescence in MCF-10A mammary epithelial cells. However, it is unknown whether this loop is involved in skin ageing. On the other hand, ultraviolet B (UVB) rays are assumed to be the main culprits for photoageing of the epidermis, but the underlying mechanisms are obscure.

AIMS

To investigate whether MM1/ΔNp63α axis is involved in UVB-induced photoageing of the epidermis.

MATERIALS AND METHODS

HaCaT human immortalized keratinocytes overexpressed with MM1, knocked down with c-Myc or irradiated with UVB, were subjected to MTT assays to measure cell proliferation, as well as RT-qPCR or immunoblot to detect the members of MM1/ΔNp63α loop and the cellular senescence markers. Meanwhile, primary normal human keratinocytes (NHKs) or mice were irradiated with UVB, followed by immunoblot analysis, SA-β-gal, haematoxylin-eosin or immunohistochemistry staining.

RESULTS

Overexpression of MM1 down-regulated ΔNp63α and induced proliferative senescence in the HaCaT cells. In the HaCaT cells, NHKs and the mouse epidermis, UVB irradiation increased MM1 mRNA level and led to a down-regulation of ΔNp63α, HERC3 and c-Myc, concomitant with cellular senescence or photoageing. Additionally, knock-down of c-Myc induced proliferative senescence in the HaCaT cells and abrogated UVB-induced cellular senescence.

CONCLUSIONS

UVB up-regulates MM1 and consequently modulates ΔNp63α and c-Myc, which may account for the proliferative senescence of keratinocytes and photoageing of the epidermis.

Prefoldin subunit MM1 promotes cell migration via facilitating filopodia formation

c-Myc modulator 1 (MM1), also known as PFDN5, is the fifth subunit of prefoldin. It was previously reported that MM1-based prefoldin promotes folding of actin during assembly of cytoskeleton, which plays key roles in cell migration. However, no evidence supports that MM1 affects cell migration. In the present study, we found that MM1 promotes cell migration in multiple cell lines. Further study revealed that MM1 promotes polymerization of β-actin into filamentous form and increases both density and length of filopodia. Effects of MM1 on filopodia formation and cell migration depend on its prefoldin activity. Though c-Myc is repressed by MM1, simultaneous knock-down of c-Myc fails to rescue migration inhibition induced by MM1 ablation. Taken together, we here, for the first time, report that prefoldin subunit MM1 is involved in cell migration; this involvement of MM1 in cell migration is due to its prefoldin activity to boost polymerization of β-actin during filopodia formation. Our findings may be helpful to elucidate the mechanism of cell migration and cancer metastasis.

Perturbation-based gene regulatory network inference to unravel oncogenic mechanisms

The gene regulatory network (GRN) of human cells encodes mechanisms to ensure proper functioning. However, if this GRN is dysregulated, the cell may enter into a disease state such as cancer. Understanding the GRN as a system can therefore help identify novel mechanisms underlying disease, which can lead to new therapies. To deduce regulatory interactions relevant to cancer, we applied a recent computational inference framework to data from perturbation experiments in squamous carcinoma cell line A431. GRNs were inferred using several methods, and the false discovery rate was controlled by the NestBoot framework. We developed a novel approach to assess the predictiveness of inferred GRNs against validation data, despite the lack of a gold standard. The best GRN was significantly more predictive than the null model, both in cross-validated benchmarks and for an independent dataset of the same genes under a different perturbation design. The inferred GRN captures many known regulatory interactions central to cancer-relevant processes in addition to predicting many novel interactions, some of which were experimentally validated, thus providing mechanistic insights that are useful for future cancer research.

The functions and mechanisms of prefoldin complex and prefoldin-subunits

The correct folding is a key process for a protein to acquire its functional structure and conformation. Prefoldin is a well-known chaperone protein that regulates the correct folding of proteins. Prefoldin plays a crucial role in the pathogenesis of common neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, and Huntington's disease). The important role of prefoldin in emerging fields (such as nanoparticles, biomaterials) and tumors has attracted widespread attention. Also, each of the prefoldin subunits has different and independent functions from the prefoldin complex. It has abnormal expression in different tumors and plays an important role in tumorigenesis and development, especially c-Myc binding protein MM-1. MM-1 can inhibit the activity of c-Myc through various mechanisms to regulate tumor growth. Therefore, an in-depth analysis of the complex functions of prefoldin and their subunits is helpful to understand the mechanisms of protein misfolding and the pathogenesis of diseases caused by misfolded aggregation.

Deubiquitinase ubiquitin-specific protease 9X regulates the stability and function of E3 ubiquitin ligase ring finger protein 115 in breast cancer cells

The E3 ubiquitin ligase ring finger protein 115 (RNF115) is overexpressed in more than half of human breast tumors and is implicated in the pathogenesis and progression of breast cancer. However, the mechanism behind RNF115 overexpression in breast tumors remains largely unknown. Here we report that ubiquitin‐specific protease 9X (USP9X), a substrate‐specific deubiquitinating enzyme, stabilizes RNF115 and thereby regulates its biological functions in breast cancer cells. Immunoprecipitation and GST pull‐down assays showed that USP9X interacted with RNF115. Depletion of RNF115 by siRNAs or overexpression of RNF115 did not significantly affect USP9X expression. In contrast, knockdown of USP9X in breast cancer cells by siRNAs reduced RNF115 protein abundance, which was partially restored following treatment with proteasome inhibitor MG‐132. Moreover, depletion of USP9X reduced the half‐life of RNF115 and increased its ubiquitination. Conversely, overexpression of USP9X resulted in an accumulation of RNF115 protein, accompanied by a decrease in its ubiquitination. RNF115 mRNA levels were unaffected by overexpression or knockdown of USP9X. Furthermore, USP9X protein expression levels correlated positively with RNF115 in breast cancer cell lines and breast tumor samples. Importantly, reintroduction of RNF115 in USP9X‐depleted cells partially rescued the reduced proliferation, migration, and invasion of breast cancer cells by USP9X knockdown. Collectively, these findings indicate that USP9X is a stabilizer of RNF115 protein and that the USP9X‐RNF115 signaling axis is implicated in the breast cancer malignant phenotype.

ΔNp63α down-regulates c-Myc modulator MM1 via E3 ligase HERC3 in the regulation of cell senescence

p63 and c-Myc are key transcription factors controlling genes involved in the cell cycle and cellular senescence. We previously reported that p63α can destabilize MM1 protein to derepress c-Myc, resulting in cell cycle progress and tumorigenesis. However, how the proteasomal degradation of MM1 is facilitated remains unclear. In the present study, we identified a novel E3 ligase, HERC3, which can mediate ubiquitination of MM1 and promote its proteasome-dependent degradation. We found that ΔNp63α transcriptionally up-regulates HERC3 and knockdown of HERC3 abrogates ΔNp63α-induced down-regulation of MM1. Either overexpression of MM1 or ablation of HERC3 induces cell senescence, while knockdown of MM1 rescues cell senescence induced by deficiency of either ΔNp63α or HERC3, implicating the involvement of the ΔNp63α/HERC3/MM1/c-Myc axis in the modulation of cell senescence. Additionally, our Oncomine analysis indicates activation of the ΔNp63α/HERC3/MM1/c-Myc axis in invasive breast carcinoma. Together, our data illuminate a novel axis regulating cell senescence: ΔNp63α stimulates transcription of E3 ligase HERC3, which mediates ubiquitination of c-Myc modulator MM1 and targets it to proteasomal degradation; subsequently, c-Myc is derepressed by ΔNp63α, thereby cell senescence is modulated by this axis. Our work provides a new interpretation of crosstalk between p63 and c-Myc, and also sheds new light on ΔNp63α-controlled cell senescence and tumorigenesis.

Functional Contributions of Prefoldin to Gene Expression

Prefoldin is a co-chaperone that evolutionarily originates in archaea, is universally present in all eukaryotes and acts as a co-chaperone by facilitating the supply of unfolded or partially folded substrates to class II chaperonins. Eukaryotic prefoldin is known mainly for its functional relevance in the cytoplasmic folding of actin and tubulin monomers during cytoskeleton assembly. However, the role of prefoldin in chaperonin-mediated folding is not restricted to cytoskeleton components, but extends to both the assembly of other cytoplasmic complexes and the maintenance of functional proteins by avoiding protein aggregation and facilitating proteolytic degradation. Evolution has favoured the diversification of prefoldin subunits, and has allowed the so-called prefoldin-like complex, with specialised functions, to appear. Subunits of both canonical and prefoldin-like complexes have also been found in the nucleus of yeast and metazoan cells, where they have been functionally connected with different gene expression steps. Plant prefoldin has also been detected in the nucleus and is physically associated with a gene regulator. Here we summarise information available on the functional involvement of prefoldin in gene expression, and discuss the implications of these results for the relationship between prefoldin structure and function.

Prefoldins Negatively Regulate Cold Acclimation in Arabidopsis thaliana by Promoting Nuclear Proteasome-Mediated HY5 Degradation

The process of cold acclimation is an important adaptive response whereby many plants from temperate regions increase their freezing tolerance after being exposed to low non-freezing temperatures. The correct development of this response relies on proper accumulation of a number of transcription factors that regulate expression patterns of cold-responsive genes. Multiple studies have revealed a variety of molecular mechanisms involved in promoting the accumulation of these transcription factors. Interestingly, however, the mechanisms implicated in controlling such accumulation to ensure their adequate levels remain largely unknown. In this work, we demonstrate that prefoldins (PFDs) control the levels of HY5, an Arabidopsis transcription factor with a key role in cold acclimation by activating anthocyanin biosynthesis, in response to low temperature. Our results show that, under cold conditions, PFDs accumulate into the nucleus through a DELLA-dependent mechanism, where they interact with HY5, triggering its ubiquitination and subsequent degradation. The degradation of HY5 would result, in turn, in anthocyanin biosynthesis attenuation, ensuring the accurate development of cold acclimation. These findings uncover an unanticipated nuclear function for PFDs in plant responses to abiotic stresses.

Prefoldin 1 promotes EMT and lung cancer progression by suppressing cyclin A expression

Prefoldin (PFDN) is a co-chaperone protein that is primarily known for its classic cytoplasmic functions in the folding of actin and tubulin monomers during cytoskeletal assembly. Here, we report a marked increase in prefoldin subunit 1 (PFDN1) levels during the transforming growth factor (TGF)-β1-mediated epithelial-mesenchymal transition (EMT) and in human lung tumor tissues. Interestingly, the nuclear localization of PFDN1 was also detected. These observations suggest that PFDN1 may be essential for important novel functions. Overexpression of PFDN1 induced EMT and cell invasion. In sharp contrast, knockdown of PFDN1 generated the opposite effects. Overexpression of PFDN1 was also found to induce lung tumor growth and metastasis. Further experiments showed that PFDN1 overexpression inhibits the expression of cyclin A. PFDN1 suppressed cyclin A expression by directly interacting with the cyclin A promoter at the transcriptional start site. Strikingly, cyclin A overexpression abolished the above PFDN1-mediated effects on the behavior of lung cancer cells, whereas cyclin A knockdown alone induced EMT and increased cell migration and invasion ability. This study reveals that the TGF-β1/PFDN1/cyclin A axis is essential for EMT induction and metastasis of lung cancer cells.

Common mechanisms of onset of cancer and neurodegenerative diseases

Onset of cancer and neurodegenerative disease occurs by abnormal cell growth and neuronal cell death, respectively, and the number of patients with both diseases has been increasing in parallel with an increase in mean lifetime, especially in developed countries. Although both diseases are sporadic, about 10% of the diseases are genetically inherited, and analyses of such familial forms of gene products have contributed to an understanding of the molecular mechanisms underlying the onset and pathogenesis of these diseases. I have been working on c-myc, a protooncogene, for a long time and identified various c-Myc-binding proteins that play roles in c-Myc-derived tumorigenesis. Among these proteins, some proteins have been found to be also responsible for the onset of neurodegenerative diseases, including Parkinson's disease, retinitis pigmentosa and cerebellar atrophy. In this review, I summarize our findings indicating the common mechanisms of onset between cancer and neurodegenerative diseases, with a focus on genes such as DJ-1 and Myc-Modulator 1 (MM-1) and signaling pathways that contribute to the onset and pathogenesis of cancer and neurodegenerative diseases.

Deficiency of spermatogenesis and reduced expression of spermatogenesis-related genes in prefoldin 5-mutant mice

MM-1α is a c-Myc-binding protein and acts as a transcriptional co-repressor in the nucleus. MM-1α is also PDF5, a subunit of prefoldin that is chaperon comprised of six subunits and prevents misfolding of newly synthesized nascent polypeptides. Prefoldin also plays a role in quality control against protein aggregation. It has been reported that mice harboring the missense mutation L110R of MM-1α/PFD5 exhibit neurodegeneration in the cerebellum and also male infertility, but the phenotype of infertility has not been fully characterized. In this study, we first analyzed morphology of the testis and epididymis of L110R of MM-1α mice. During differentiation of spermatogenesis, spermatogonia, spermatocytes and round spermatids were formed, but formation of elongated spermatids was compromised in L110R MM-1α mice. Furthermore, reduced number/concentration of sperm in the epididymis was observed. MM-1α was strongly expressed in the round spermatids and sperms with round spermatids, suggesting that MM-1α affects the differentiation and maturation of germ cells. Changes in expression levels of spermatogenesis-related genes in mice testes were then examined. The fatty-acid-binding protein (fabp4) gene was up-regulated and three genes, including sperm-associated glutamate (E)-rich protein 4d (speer-4d), phospholipase A2-Group 3 (pla2g3) and phospholipase A2-Group 10 (pla2g10), were down-regulated in L110R MM-1α mice. L110R MM-1α and wild-type MM-1α bound to regions of up-regulated and down-regulated genes, respectively. Since these gene products are known to play a role in maturation and motility of sperm, a defect of at least MM-1α transcriptional activity is thought to induce expressional changes of these genes, resulting in male infertility.

Nuclear functions of prefoldin

Prefoldin is a cochaperone, present in all eukaryotes, that cooperates with the chaperonin CCT. It is known mainly for its functional relevance in the cytoplasmic folding of actin and tubulin monomers during cytoskeleton assembly. However, both canonical and prefoldin-like subunits of this heterohexameric complex have also been found in the nucleus, and are functionally connected with nuclear processes in yeast and metazoa. Plant prefoldin has also been detected in the nucleus and physically associated with a gene regulator. In this review, we summarize the information available on the involvement of prefoldin in nuclear phenomena, place special emphasis on gene transcription, and discuss the possibility of a global coordination between gene regulation and cytoplasmic dynamics mediated by prefoldin.

Expansion and diversification of BTL ring-H2 ubiquitin ligases in angiosperms: putative Rabring7/BCA2 orthologs

RING finger E3 ligases are components of the ubiquitin proteasome system (UPS) that mediate the transfer of ubiquitin to substrates. Single-subunit RING finger E3s binds the E2 ubiquitin-conjugating enzyme and contains recognition sequences for the substrate within the same polypeptide. Here we describe the characterization of a class of RING finger E3 ligases that is conserved among eukaryotes. This class encodes a RING-H2 domain related in sequence to the ATL RING-H2 domain, another class of E3 ligases, and a C2/C2 zing finger at the amino-terminus, formerly described as BZF. In viridiplantae (green algae and land plants), we designed this family as BTL for BZF ATLs. BTLs are putative orthologs of the mammalian Rabring7/BCA2 RING-H2 E3s that have expanded in angiosperms. They are found in numbers ranging from three to thirty-one, which is in contrast to the one to three members normally found in animals, fungi, and protists. Furthermore, the number of sequence LOGOs generated in angiosperms is four times greater than that in other eukaryotes. In contrast to ATLs, which show expansion by tandem duplication, tandemly duplicated BTLs are scarce. The mode of action of Rabring7/BCA2 and BTLs may be similar since both the Rabring7/BCA2 BZF and the ath|BTL4 BZF are likely to mediate the binding of ubiquitin. This study introduces valuable information on the evolution and domain structure of the Rabring7/BCA2/BTL class of E3 ligases which may be important for core eukaryotic genes.

DJ-1 cooperates with PYCR1 in cell protection against oxidative stress

DJ-1, a product of the DJ-1/PARK7 gene, has been suggested to play various functions involved in transcriptional regulation, protease activity, anti-oxidative stress activity, and regulation of mitochondrial complex I. Such a variety of functions of DJ-1 are supposed to be realized through interactions with different partner proteins. Among the candidates for DJ-1-partner proteins detected in TOF-MAS analyses of the cellular proteins co-immunoprecipitated with DJ-1, we focused here pyrroline-5-carboxylate reductase 1, PYCR1, a final key enzyme for proline biosynthesis. DJ-1 directly bound to PYCR1 in vivo and in vitro. DJ-1 and PYCR1 colocalized in mitochondria, and both were suggested to be involved in regulation of mitochondrial membrane potential, but differently. DJ-1 enhanced the enzymatic activity of PYCR1 in vitro. The cells knocked down for DJ-1 and PYCR1 showed lower viability under oxidative stress conditions. No additive nor synergistic results were obtained for the cells that had been knocked down for both DJ-1 and PYCR1, suggesting that DJ-1 and PYCR1 are on the same pathway of anti-oxidative stress protection of the cells.