Hyaluronan binding protein 1 (HABP1)/C1QBP/p32 is an endogenous substrate for MAP kinase and is translocated to the nucleus upon mitogenic stimulation

Biomimetic Hyaluronan Binding Biomaterials to Capture the Complex Regulation of Hyaluronan in Tissue Development and Function

Within native ECM, Hyaluronan (HA) undergoes remarkable structural remodeling through its binding receptors and proteins called hyaladherins. Hyaladherins contain a group of tandem repeat sequences, such as LINK domains, BxB7 homologous sequences, or 20-50 amino acid long short peptide sequences that have high affinity towards side chains of HA. The HA binding sequences are critical players in HA distribution and regulation within tissues and potentially attractive therapeutic targets to regulate HA synthesis and organization. While HA is a versatile and successful biopolymer, most HA-based therapeutics have major differences from a native HA molecule, such as molecular weight discrepancies, crosslinking state, and remodeling with other HA binding proteins. Recent studies showed the promise of HA binding domains being used as therapeutic biomaterials for osteoarthritic, ocular, or cardiovascular therapeutic products. However, we propose that there is a significant potential for HA binding materials to reveal the physiological functions of HA in a more realistic setting. This review is focused on giving a comprehensive overview of the connections between HA's role in the body and the potential of HA binding material applications in therapeutics and regenerative medicine. We begin with an introduction to HA then discuss HA binding molecules and the process of HA binding. Finally, we discuss HA binding materials anf the future prospects of potential HA binding biomaterials systems in the field of biomaterials and tissue engineering.

An approach to p32/gC1qR/HABP1: a multifunctional protein with an essential role in cancer

P32/gC1qR/HABP1 is a doughnut-shaped acidic protein, highly conserved in eukaryote evolution and ubiquitous in the organism. Although its canonical subcellular localization is the mitochondria, p32 can also be found in the cytosol, nucleus, cytoplasmic membrane, and it can be secreted. Therefore, it is considered a multicompartmental protein. P32 can interact with many physiologically divergent ligands in each subcellular location and modulate their functions. The main ligands are C1q, hyaluronic acid, calreticulin, CD44, integrins, PKC, splicing factor ASF/SF2, and several microbial proteins. Among the functions in which p32 participates are mitochondrial metabolism and dynamics, apoptosis, splicing, immune response, inflammation, and modulates several cell signaling pathways. Notably, p32 is overexpressed in a significant number of epithelial tumors, where its expression level negatively correlates with patient survival. Several studies of gain and/or loss of function in cancer cells have demonstrated that p32 is a promoter of malignant hallmarks such as proliferation, cell survival, chemoresistance, angiogenesis, immunoregulation, migration, invasion, and metastasis. All of this strongly suggests that p32 is a potential diagnostic molecule and therapeutic target in cancer. Indeed, preclinical advances have been made in developing therapeutic strategies using p32 as a target. They include tumor homing peptides, monoclonal antibodies, an intracellular inhibitor, a p32 peptide vaccine, and p32 CAR T cells. These advances are promising and will allow soon to include p32 as part of targeted cancer therapies.

Identification of the hyaluronic acid pathway as a therapeutic target for facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is linked to epigenetic derepression of the germline/embryonic transcription factor DUX4 in skeletal muscle. However, the etiology of muscle pathology is not fully understood, as DUX4 misexpression is not tightly correlated with disease severity. Using a DUX4-inducible cell model, we show that multiple DUX4-induced molecular pathologies that have been observed in patient-derived disease models are mediated by the signaling molecule hyaluronic acid (HA), which accumulates following DUX4 induction. These pathologies include formation of RNA granules, FUS aggregation, DNA damage, caspase activation, and cell death. We also observe previously unidentified pathologies including mislocalization of mitochondria and the DUX4- and HA-binding protein C1QBP. These pathologies are prevented by 4-methylumbelliferone, an inhibitor of HA biosynthesis. Critically, 4-methylumbelliferone does not disrupt DUX4-C1QBP binding and has only a limited effect on DUX4 transcriptional activity, establishing that HA signaling has a central function in pathology and is a target for FSHD therapeutics.

Intracrine Endorphinergic Systems in Modulation of Myocardial Differentiation

A wide variety of peptides not only interact with the cell surface, but govern complex signaling from inside the cell. This has been referred to as an "intracrine" action, and the orchestrating molecules as "intracrines". Here, we review the intracrine action of dynorphin B, a bioactive end-product of the prodynorphin gene, on nuclear opioid receptors and nuclear protein kinase C signaling to stimulate the transcription of a gene program of cardiogenesis. The ability of intracrine dynorphin B to prime the transcription of its own coding gene in isolated nuclei is discussed as a feed-forward loop of gene expression amplification and synchronization. We describe the role of hyaluronan mixed esters of butyric and retinoic acids as synthetic intracrines, controlling prodynorphin gene expression, cardiogenesis, and cardiac repair. We also discuss the increase in prodynorphin gene transcription and intracellular dynorphin B afforded by electromagnetic fields in stem cells, as a mechanism of cardiogenic signaling and enhancement in the yield of stem cell-derived cardiomyocytes. We underline the possibility of using the diffusive features of physical energies to modulate intracrinergic systems without the needs of viral vector-mediated gene transfer technologies, and prompt the exploration of this hypothesis in the near future.

Systematic Multiomics Analysis of Alterations in C1QBP mRNA Expression and Relevance for Clinical Outcomes in Cancers

C1QBP (Complement Component 1 Q Subcomponent-Binding Protein), a multicompartmental protein, participates in various cellular processes, including mRNA splicing, ribosome biogenesis, protein synthesis in mitochondria, apoptosis, transcriptional regulation, and infection processes of viruses. The correlation of C1QBP expression with patient survival and molecular function of C1QBP in relation to cancer progression has not been comprehensively studied. Therefore, we sought to systematically investigate the expression of C1QBP to evaluate the change of C1QBP expression and the relationship with patient survival and affected pathways in breast, lung, colon, and bladder cancers as well as lymphoma. Relative expression levels of C1QBP were analyzed using the Oncomine, Gene Expression Across Normal and Tumor Tissue (GENT), and The Cancer Genome Atlas (TCGA) databases. Mutations and copy number alterations in C1QBP were also analyzed using cBioPortal, and subsequently, the relationship between C1QBP expression and survival probability of cancer patients was explored using the PrognoScan database and the R2: Kaplan Meier Scanner. Additionally, the relative expression of C1QBP in other cancers, and correlation of C1QBP expression with patient survival were investigated. Gene ontology and pathway analysis of commonly differentially coexpressed genes with C1QBP in breast, lung, colon, and bladder cancers as well as lymphoma revealed the C1QBP-correlated pathways in these cancers. This data-driven study demonstrates the correlation of C1QBP expression with patient survival and identifies possible C1QBP-involved pathways, which may serve as targets of a novel therapeutic modality for various human cancers.

Complement component 1q subcomponent binding protein in the brain of the rat

Complement component 1q subcomponent binding protein (C1qbp) is a multifunctional protein involved in immune response, energy homeostasis of cells as a plasma membrane receptor, and a nuclear, cytoplasmic or mitochondrial protein. Recent reports suggested its neuronal function, too, possibly in axon maintenance, synaptic function, and neuroplasticity. Therefore, we addressed to identify C1qbp in the rat brain using in situ hybridization histochemistry and immunolabelling at light and electron microscopic level. C1qbp has a topographical distribution in the brain established by the same pattern of C1qbp mRNA-expressing and protein-containing neurons with the highest abundance in the cerebral cortex, anterodorsal thalamic nucleus, hypothalamic paraventricular (PVN) and arcuate nuclei, spinal trigeminal nucleus. Double labelling of C1qbp with the neuronal marker NeuN, with the astrocyte marker S100, and the microglia marker Iba1 demonstrated the presence of C1qbp in neurons but not in glial cells in the normal brain, while C1qbp appeared in microglia following their activation induced by focal ischemic lesion. Only restricted neurons expressed C1qbp, for example, in the PVN, magnocellular neurons selectively contained C1qbp. Further double labelling by using the mitochondria marker Idh3a antibody suggested the mitochondrial localization of C1qbp in the brain, confirmed by correlated light and electron microscopy at 3 different brain regions. Post-embedding immunoelectron microscopy also suggested uneven C1qbp content of mitochondria in different brain areas but also heterogeneity within single neurons. These data suggest a specific function of C1qbp in the brain related to mitochondria, such as the regulation of local energy supply in neuronal cells.

High molecular weight fibroblast growth factor 2 induces apoptosis by interacting with complement component 1 Q subcomponent-binding protein in vitro

Fibroblast growth factor 2 (FGF2) is a multifunctional cell growth factor that regulates cell proliferation, differentiation, adhesion, migration, and apoptosis. FGF2 has multiple isoforms, including an 18-kDa low molecular weight isoform (lo-FGF2) and 22-, 23-, 24-, and 34-kDa high molecular weight isoforms (hi-FGF2). Hi-FGF2 overexpression induces chromatin compaction, which requires the mitochondria and leads to apoptosis. Complement component 1 Q subcomponent-binding protein (C1QBP) plays an important role in mitochondria-dependent apoptosis by regulating the opening of the mitochondrial permeability transition pore. However, the interaction between C1QBP and hi-FGF2 and its role in hi-FGF2-mediated apoptosis remain unclear. Here, we found that hi-FGF2 overexpression induced depolarization of the mitochondrial membrane, cytochrome c release into the cytosol, and a considerable increase in C1QBP messenger RNA and protein expression. Furthermore, coimmunoprecipitation results showed that the mitochondrial protein, C1QBP, interacts with hi-FGF2. C1QBP knockdown using small interfering RNA significantly decreased the localization of hi-FGF2 to the mitochondria and increased the rate of apoptosis. Our results highlight a novel mechanism underlying hi-FGF2-induced, mitochondria-driven cell death involving the direct interaction between hi-FGF2 and C1QBP and the upregulation of C1QBP expression.

Y-box protein-associated acidic protein (YBAP1/C1QBP) affects the localization and cytoplasmic functions of YB-1

The Y-box proteins are multifunctional nucleic acid-binding proteins involved in various aspects of gene regulation. The founding member of the Y-box protein family, YB-1, functions as a transcription factor as well as a principal component of messenger ribonucleoprotein particles (mRNPs) in somatic cells. The nuclear level of YB-1 is well correlated with poor prognosis in many human cancers. Previously, we showed that a Y-box protein–associated acidic protein, YBAP1, which is identical to complement component 1, q subcomponent-binding protein (C1QBP, also called gC1qR, hyaluronan-binding protein 1 [HABP1] or ASF/SF2-associated protein p32), relieves translational repression by YB-1. Here we show that the nuclear localization of YB-1 harboring a point mutation in the cold shock domain was inhibited when co-expressed with YBAP1, whereas cytoplasmic accumulation of the wild-type YB-1 was not affected. We showed that YBAP1 inhibited the interaction between YB-1 and transportin 1. In the cytoplasm, YBAP1 affected the accumulation of YB-1 to processing bodies (P-bodies) and partially abrogated the mRNA stabilization by YB-1. Our results, indicating that YBAP1/C1QBP regulates the nucleo-cytoplasmic distribution of YB-1 and its cytoplasmic functions, are consistent with a model that YBAP1/C1QBP acts as an mRNP remodeling factor.

Multi-functional, multicompartmental hyaluronan-binding protein 1 (HABP1/p32/gC1qR): implication in cancer progression and metastasis

Cancer is a complex, multi-factorial, multi-stage disease and a global threat to human health. Early detection of nature and stage of cancer is highly crucial for disease management. Recent studies have proved beyond any doubt about the involvement of the ubiquitous, myriad ligand binding, multi-functional human protein, hyaluronan-binding protein 1 (HABP1), which is identical to the splicing factor associated protein (p32) and the receptor of the globular head of the complement component (gC1qR) in tumorigenesis and cancer metastasis. Simultaneously three laboratories have discovered and named this protein separately as mentioned. Subsequently, different scientists have worked on the distinct functions in cellular processes ranging from immunological response, splicing mechanism, sperm-oocyte interactions, cell cycle regulation to cancer and have concentrated in their respective area of interest, referring it as either p32 or gC1qR or HABP1. HABP1 overexpression has been reported in almost all the tissue-specific forms of cancer and correlated with stage and poor prognosis in patients. In order to tackle this deadly disease and for therapeutic intervention, it is imperative to focus on all the regulatory aspects of this protein. Hence, this work is an attempt to combine an assortment of information on this protein to have an overview, which suggests its use as a diagnostic marker for cancer. The knowledge might assist in the designing of drugs for therapeutic intervention of HABP1/p32/gC1qR regulated specific ligand mediated pathways in cancer.

C1QBP is upregulated in colon cancer and binds to apolipoprotein A-I

The present study aimed to investigate the expression of complement component 1, q subcomponent-binding protein (C1QBP) in colon cancer cells, and identify proteins that interact with C1QBP. Total proteins were extracted from both the tumor and normal tissues of 22 patients with colon cancer and analyzed using liquid chromatography-mass spectrometry (LC-MS) to identify proteins that were differentially-expressed in tumor tissues. C1QBP overexpression was induced in 293T cells using a pFLAG-CMV2 expression vector. Overexpressed FLAG-tagged C1QBP protein was then immunoprecipitated using anti-FLAG antibodies and C1QBP-interacting proteins were screened using LC-MS analysis of the immunoprecipitates. The C1QBP-interacting proteins were confirmed using reverse-immunoprecipitation and the differential expression of C1QBP in tissues and cell lines was confirmed using western blot analysis. LC-MS analysis revealed that C1QBP exhibited a typical tumor expression pattern. Two immune-reactive signals (33 and 14 kDa) were detected in normal and tumor tissues from 19 patients. Furthermore, 14 kDa C1QBP protein was upregulated in the tumors of 15 patients. In total, 39 proteins were identified as candidate C1QBP-interacting proteins, and an interaction between C1QBP and apolipoprotein A-I was confirmed. The present study indicates that C1QBP is involved in colon cancer carcinogenesis, and that the mechanisms underlying the established anti-tumor properties of apolipoprotein A-I may include interacting with and inhibiting the activity of C1QBP.

Synaptic proteome changes in the hypothalamus of mother rats

To establish synaptic proteome changes associated with motherhood, we isolated synaptosome fractions from the hypothalamus of mother rats and non-maternal control females at the 11th postpartum day. Proteomic analysis by two-dimensional differential gel electrophoresis combined with mass spectrometric protein identification established 26 significant proteins, 7 increasing and 19 decreasing protein levels in the dams. The altered proteins are mainly involved in energy homeostasis, protein folding, and metabolic processes suggesting the involvement of these cellular processes in maternal adaptations. The decrease in a significantly altered protein, complement component 1q subcomponent-binding protein (C1qbp) was validated with Western blotting. Furthermore, immunohistochemistry showed its presence in hypothalamic fibers and terminals in agreement with its presence in synaptosomes. We also found the expression of C1qbp in different hypothalamic nuclei including the preoptic area and the paraventricular hypothalamic nucleus at the protein and at the mRNA level using immunohistochemistry and in situ hybridization histochemistry, respectively. Bioinformatical network analysis revealed that cytokines, growth factors, and protein kinases are common regulators, which indicates a complex regulation of the proteome change in mothers. The results suggest that maternal responsiveness is associated with synaptic proteins level changes in the hypothalamus, and that growth factors and cytokines may govern these alterations.

BIOLOGICAL SIGNIFICANCE

The period of motherhood is accompanied with several behavioral, neuroendocrine, emotional and metabolic adaptations in the brain. Although it is established that various hypothalamic networks participate in the maternal adaptations of the rodent brain, our knowledge on the molecular background of these alterations remains seriously limited. In the present study, we first determined that the functional alterations of the maternal brain can be detected at the level of the synaptic proteome in the hypothalamus. Independent confirmation of synaptic localization, and also the established decrease in the level of C1qbp protein suggest the validity of the data. Common regulators of altered proteins belonging to the growth factor and cytokine family suggest that the synaptic adaptation is governed by these extracellular signals and future studies should focus on their specific roles. Our study was also the first to describe the expression pattern of C1qbp in the hypothalamus, a protein potentially involved in mitochondrial and neuroimmunological regulations of synaptic plasticity. Its presence in the preoptic area responsible for maternal behaviors and also in the paraventricular hypothalamic and arcuate nuclei regulating hormonal levels suggests that the same proteins may be involved in different aspects of maternal adaptations. The conclusions of the present work contribute to establishing the molecular alterations that determine different maternal adaptations in the brain. Since maternal changes are models of neuronal plasticity in all social interactions, the reported results can affect a wide field of molecular and behavioral neuroscience.

Hyaluronic acid binding protein 1 overexpression is an indicator for disease-free survival in cervical cancer

BACKGOUND

Hyaluronic acid binding protein 1 (HABP1) is reported to overexpress in various cancer tissues and may therefore contribute to oncogenesis. However, the status of HABP1 expression in cervical cancer (CC) remains unknown. The aim of this study was to investigate the role of HABP1 and its relationship with clinical characteristics in patients with CC.

METHODS

Immunohistochemistry was used to explore the expression of HABP1 in 30 cervical intra-epithelial neoplasia (CIN) and 118 CC specimens compared to 10 normal cervical specimens.

RESULTS

HABP1 expression was found to be positively higher in CC than in CIN2/3 cases (P = 0.020). Moreover, clinicopathological analysis showed that HABP1 overexpression was associated with advanced FIGO stage (P = 0.001), poor histologic grade (P = 0.013), large tumor size (P = 0.025), LVSI (P = 0.024), deep stromal infiltration (P = 0.001), and lymph node metastasis (P = 0.023). Multivariate analysis suggested that HABP1 overexpression was an independent factor for disease-free survival (DFS) (hazard ratio 3.082; 95% confidence interval 1.372-7.501; P = 0.007).

CONCLUSIONS

The present data provide evidence that HABP1 overexpression predicts CC with high-risk factors and may therefore serve as a new molecular marker for the prediction of DFS in these patients.

Elevated HABP1 protein expression correlates with progression and poor survival in patients with gastric cancer

BACKGROUND

Hyaluronic acid-binding protein 1 (HABP1/gC1qR/p32) has been recently implicated in oncogenesis and cancer progression in various malignancies; however, its clinical role in gastric cancer (GC) is still unclear.

PATIENTS AND METHODS

First, HABP1 expression was determined by Western blot analysis and immunohistochemistry. Then, we evaluated the expression of HABP1 and its clinical significance in tumor tissues from 181 patients with GC.

RESULTS

Expression of HABP1 protein in GC tissues was noticeably higher than that in adjacent nonneoplastic tissues (P=0.018). Increased HABP1 expression was significantly associated with tumor, node, and metastasis (TNM) stage (P=0.006), depth of invasion (P=0.001), lymph node metastasis (P=0.001), liver metastasis (P=0.024), and peritoneum metastasis (P=0.009). Patients with high expression of HABP1 had poor overall survival rate (P<0.001). In addition, histologic grade (P=0.017), TNM stage (P<0.001), Borrmann grouping (P<0.001), depth of invasion (P<0.001), lymph node metastasis (P<0.001), liver metastasis (P=0.010), and tumor size (P<0.001) were independent prognostic factors for overall survival. Multivariate Cox regression analysis revealed that HABP1 (P=0.004), histologic grade (P=0.047), TNM stage (P<0.001), Borrmann grouping (P<0.001), and liver metastasis (P=0.038) were independent factors for overall survival in patients with GC.

CONCLUSION

These findings demonstrated that HABP1 was an indicator for GC progression and poor survival, which highlighted its potential role as a therapeutic target for GCs.

Exposure of cultured fibroblasts to the peptide PR-11 for the identification of induced proteome alterations and discovery of novel potential ligands

The PR-11 peptide corresponds to the N-terminal and active region of the endogenously synthesized PR-39 molecule, of porcine origin. It is known to possess various biological effects including antimicrobial properties, angiogenic and anti-inflammatory activities. Apart from its reported activity as a proteasome inhibitor, a more comprehensive understanding of its function, at the molecular level, is still lacking. In this study, we used a label-free shotgun strategy to evaluate the proteomic alterations caused by exposure of cultured fibroblasts to the peptide PR-11. This approach revealed that more than half of the identified molecules were related to signalling, transcription and translation. Proteins directly associated to regulation of angiogenesis and interaction with the hypoxia-inducible factor 1-α (HIF-1α) were significantly altered. In addition, at least three differentially expressed molecules of the NF-κB pathway were detected, suggesting an anti-inflammatory property of PR-11. At last, we demonstrated novel potential ligands of PR-11, through its immobilization for affinity chromatography. Among the eluted molecules, gC1qR, a known complement receptor, appeared markedly enriched. This provided preliminary evidence of a PR-11 ligand possibly involved in the internalization of this peptide. Altogether, our findings contributed to a better understanding of the cellular pathways affected by PR-39 derived molecules.

REAC technology and hyaluron synthase 2, an interesting network to slow down stem cell senescence

Hyaluronic acid (HA) plays a fundamental role in cell polarity and hydrodynamic processes, affording significant modulation of proliferation, migration, morphogenesis and senescence, with deep implication in the ability of stem cells to execute their differentiating plans. The Radio Electric Asymmetric Conveyer (REAC) technology is aimed to optimize the ions fluxes at the molecular level in order to optimize the molecular mechanisms driving cellular asymmetry and polarization. Here, we show that treatment with 4-methylumbelliferone (4-MU), a potent repressor of type 2 HA synthase and endogenous HA synthesis, dramatically antagonized the ability of REAC to recover the gene and protein expression of Bmi1, Oct4, Sox2, and Nanog in ADhMSCs that had been made senescent by prolonged culture up to the 30^th passage. In senescent ADhMSCs, 4-MU also counteracted the REAC ability to rescue the gene expression of TERT, and the associated resumption of telomerase activity. Hence, the anti-senescence action of REAC is largely dependent upon the availability of endogenous HA synthesis. Endogenous HA and HA-binding proteins with REAC technology create an interesting network that acts on the modulation of cell polarity and intracellular environment. This suggests that REAC technology is effective on an intracellular niche level of stem cell regulation.

Proteomics Analysis Reveals Novel RASSF2 Interaction Partners

RASSF2 is a tumor suppressor that shares homology with other Ras-association domain (RASSF) family members. It is a powerful pro-apoptotic K-Ras effector that is frequently inactivated in many human tumors. The exact mechanism by which RASSF2 functions is not clearly defined, but it likely acts as a scaffolding protein, modulating the activity of other pro-apoptotic effectors, thereby regulating and integrating tumor suppressor pathways. However, only a limited number of RASSF2 interacting partners have been identified to date. We used a proteomics based approach to identify additional RASSF2 interactions, and thereby gain a better insight into the mechanism of action of RASSF2. We identified several proteins, including C1QBP, Vimentin, Protein phosphatase 1G and Ribonuclease inhibitor that function in diverse biological processes, including protein post-translational modifications, epithelial-mesenchymal transition, cell migration and redox homeostasis, which have not previously been reported to interact with RASSF2. We independently validated two of these novel interactions, C1QBP and Vimentin and found that the interaction with C1QBP was enhanced by K-Ras whereas, interestingly, the Vimentin interaction was reduced by K-Ras. Additionally, RASSF2/K-Ras regulated the acetylation of Vimentin. Our data thus reveal novel mechanisms by which RASSF2 may exert its functions, several of which may be Ras-regulated.

Soluble gC1qR in Blood and Body Fluids: Examination in a Pancreatic Cancer Patient Cohort

BACKGROUND

gC1qR is a multifunctional cellular protein that has been linked to inflammation and cancer. gC1qR is highly upregulated in adenocarcinomas as compared to normal tissue counterparts, and soluble gC1qR (sgC1qR) has been detected in vitro in the pericellular milieu of proliferating malignant cells.

AIM

The present study explored the tissue expression of gC1qR in pancreatic cancer by immunohistochemistry, and the presence of sgC1qR in vivo, by examining blood and malignant effusions from patients with metastatic pancreatic adenocarcinoma.

METHODS

Tissue expression of gC1qR by pancreatic adenocarcinoma was visualized by immunohistochemistry. SgC1qR was quantified in serum from healthy volunteers (n=20) and pancreatic cancer patients (n=34), as well as in malignant pleural (n=23) and peritoneal effusions (n=27), using a newly developed, sensitive immunocapture sandwich ELISA.

RESULTS

Overexpression of gC1qR was confirmed in pancreatic adenocarcinoma compared to nonmalignant pancreatic tissue. Moreover, increased serum levels of sgC1qR (0.29 ± 0.22 ng/ml) were noted in patients with metastatic pancreatic cancer compared to healthy controls (0.15 ± 0.10 ng/ml) (mean ± S.D.) (p=0.035). In 11 of 16 patients for whom sequential samples were available, serum sgC1qR levels rose with disease progression, and paralleled changes in tumor biomarkers, CEA and CA19.9. In addition to blood, sgC1qR was detected in malignant pleural (0.55 ± 0.47 ng/ml) and peritoneal effusions (0.57 ± 0.38 ng/ml).

CONCLUSION

This study provides the first evidence for the presence of sgC1qR in vivo. The ability to detect sgC1qR in blood and body fluids will enable further studies to elucidate its pathophysiology in malignancy.

Interactions between RNA-binding proteins and P32 homologues in trypanosomes and human cells

RNA-binding proteins (RBPs) are involved in many aspects of mRNA metabolism such as splicing, nuclear export, translation, silencing, and decay. To cope with these tasks, these proteins use specialized domains such as the RNA recognition motif (RRM), the most abundant and widely spread RNA-binding domain. Although this domain was first described as a dedicated RNA-binding moiety, current evidence indicates these motifs can also engage in direct protein-protein interactions. Here, we discuss recent evidence describing the interaction between the RRM of the trypanosomatid RBP UBP1 and P22, the homolog of the human multifunctional protein P32/C1QBP. Human P32 was also identified while performing a similar interaction screening using both RRMs of TDP-43, an RBP involved in splicing regulation and Amyotrophic Lateral Sclerosis. Furthermore, we show that this interaction is mediated by RRM1. The relevance of this interaction is discussed in the context of recent TDP-43 interactomic approaches that identified P32, and the numerous evidences supporting interactions between P32 and RBPs. Finally, we discuss the vast universe of interactions involving P32, supporting its role as a molecular chaperone regulating the function of its ligands.

Association of UBP1 to ribonucleoprotein complexes is regulated by interaction with the trypanosome ortholog of the human multifunctional P32 protein

Regulation of gene expression in trypanosomatid parasitic protozoa is mainly achieved posttranscriptionally. RNA-binding proteins (RBPs) associate to 3' untranslated regions in mRNAs through dedicated domains such as the RNA recognition motif (RRM). Trypanosoma cruzi UBP1 (TcUBP1) is an RRM-type RBP involved in stabilization/degradation of mRNAs. TcUBP1 uses its RRM to associate with cytoplasmic mRNA and to mRNA granules under starvation stress. Here, we show that under starvation stress, TcUBP1 is tightly associated with condensed cytoplasmic mRNA granules. Conversely, under high nutrient/low density-growing conditions, TcUBP1 ribonucleoprotein (RNP) complexes are lax and permeable to mRNA degradation and disassembly. After dissociating from mRNA, TcUBP1 can be phosphorylated only in unstressed parasites. We have identified TcP22, the ortholog of mammalian P32/C1QBP, as an interactor of TcUBP1 RRM. Overexpression of TcP22 decreased the number of TcUBP1 granules in starved parasites in vivo. Endogenous TcUBP1 RNP complexes could be dissociated in vitro by addition of recombinant TcP22, a condition stimulating TcUBP1 phosphorylation. Biochemical and in silico analysis revealed that TcP22 interacts with the RNA-binding surface of TcUBP1 RRM. We propose a model for the decondensation of TcUBP1 RNP complexes in T. cruzi through direct interaction with TcP22 and phosphorylation.

Overexpression of HABP1 correlated with clinicopathological characteristics and unfavorable prognosis in endometrial cancer

Hyaluronic acid binding protein 1 (HABP1/gC1qR/p32), a ubiquitous multifunctional protein belonging to the hyaladherin family, has been implicated in the tumorigenesis, progression, invasion, and metastasis of several malignant tumors. However, the role of HABP1 in endometrial cancer has not yet been studied. This study aimed to detect the expression of HABP1 in endometrial cancer and explore its role in the clinicopathological features and prognosis of endometrial cancer. We analyzed HABP1 expression by immunohistochemistry in 188 endometrial cancer specimens, 43 benign endometrial lesion specimens, and 41 normal endometrium specimens and assessed using Western blot analysis. Statistical analysis showed that HABP1 was overexpressed in endometrial cancer and benign endometrial lesion compared with normal endometrium (P < 0.001 and P = 0.012, respectively). In addition, HABP1 expression was significantly higher in endometrial cancer than in benign endometrial lesion (P < 0.001). High HABP1 expression was significantly associated with advanced International Federation of Gynecology and Obstetrics stage (P = 0.019), higher histologic grade (P < 0.001), deep myometrial invasion (P = 0.013), lymphovascular space invasion (P = 0.010), lymph node metastasis (P = 0.015), and recurrence (P = 0.009). Patients with high HABP1 expression had a poorer overall survival (OS) and disease-free survival (DFS) than patients with low HABP1 expression (P = 0.015 and P = 0.012, respectively). Multivariate Cox regression analysis showed that the HABP1 expression status was an independent prognostic factor of OS and DFS (P = 0.025 and P = 0.022, respectively) in patients with endometrial cancer. Our results indicated that overexpression of HABP1 may serve as a new biomarker to predict the progression and prognosis of endometrial cancer.

Screening of differentially expressed genes related to bladder cancer and functional analysis with DNA microarray

OBJECTIVE

The purpose of this study was to identify genes related to bladder cancer with samples from normal and disease cases by microarray chip.

METHODS

After downloading the gene expression profile GSE3167 from Gene Expression Omnibus database which includes 50 bladder samples, comprising 9 normal and 41 disease samples, differentially expressed genes were identified with packages in R language. The selected differentially expressed genes were further analyzed using bioinformatics methods. Firstly, molecular functions, biological processes and cell component analysis were researched by software Gestalt. Then, software String was used to search interaction relationships among differentially expressed genes, and hub genes of the network were selected. Finally, by using plugins of software Cytoscape, Mcode and Bingo, module analysis of hub-genes was performed.

RESULTS

A total of 221 genes were identified as differentially expressed by comparing normal and disease bladder samples, and a network as well as the hub gene C1QBP was obtained from the network. The C1QBP module had the closest relationship to production of molecular mediators involved in inflammatory responses.

CONCLUSION

We obtained differentially expressed genes of bladder cancer by microarray, and both PRDX2 and YWHAZ in the module with hub gene C1QBP were most significantly related to production of molecular mediators involved in inflammatory responses. From knowledge of inflammatory responses and cancer, our results showed that, the hub gene and its module could induce inflammation in bladder cancer. These related genes are candidate bio-markers for bladder cancer diagnosis and might be helpful in designing novel therapies.

Interaction network of proteins associated with human cytomegalovirus IE2-p86 protein during infection: a proteomic analysis

Human cytomegalovirus protein IE2-p86 exerts its functions through interaction with other viral and cellular proteins. To further delineate its protein interaction network, we generated a recombinant virus expressing SG-tagged IE2-p86 and used tandem affinity purification coupled with mass spectrometry. A total of 9 viral proteins and 75 cellular proteins were found to associate with IE2-p86 protein during the first 48 hours of infection. The protein profile at 8, 24, and 48 h post infection revealed that UL84 tightly associated with IE2-p86, and more viral and cellular proteins came into association with IE2-p86 with the progression of virus infection. A computational analysis of the protein-protein interaction network indicated that all of the 9 viral proteins and most of the cellular proteins identified in the study are interconnected to varying degrees. Of the cellular proteins that were confirmed to associate with IE2-p86 by immunoprecipitation, C1QBP was further shown to be upregulated by HCMV infection and colocalized with IE2-p86, UL84 and UL44 in the virus replication compartment of the nucleus. The IE2-p86 interactome network demonstrated the temporal development of stable and abundant protein complexes that associate with IE2-p86 and provided a framework to benefit future studies of various protein complexes during HCMV infection.

Autophagic vacuolation induced by excess ROS generation in HABP1/p32/gC1qR overexpressing fibroblasts and its reversal by polymeric hyaluronan

The ubiquitous hyaladherin, hyaluronan-binding protein 1 (HABP1/p32/gC1qR) upon stable overexpression in normal fibroblasts (F-HABP07) has been reported to induce mitochondrial dysfunction, growth retardation and apoptosis after 72 h of growth. HABP1 has been observed to accumulate in the mitochondria resulting in generation of excess Reactive Oxygen Species (ROS), mitochondrial Ca⁺⁺ efflux and drop in mitochondrial membrane potential. In the present study, autophagic vacuolation was detected with monodansylcadaverin (MDC) staining from 36 h to 60 h of culture period along with elevated level of ROS in F-HABP07 cells. Increased expression of autophagic markers like MAP-LC3-II, Beclin 1 and autophagic modulator, DRAM confirmed the occurrence of the phenomenon. Reduced vacuole formation was observed upon treatment with 3-MA, a known PI3 kinase inhibitor, only at 32 h and was ineffective if treated later, as high ROS level was already attained. Treatment of F111 and F-HABP07 cells with bafilomycin A1 further indicated an increase in autophagosome formation along with autophagic degradation in HABP1 overexpressed fibroblasts. Comparison between normal fibroblast (F111) and F-HABP07 cells indicate reduced level of polymeric HA, its depolymerization and perturbed HA-HABP1 interaction in F-HABP07. Interestingly, supplementation of polymeric HA, an endogenous ROS scavenger, in the culture medium prompted reduction in number of vacuoles in F-HABP07 along with drop in ROS level, implying that excess ROS generation triggers initiation of autophagic vacuole formation prior to apoptosis due to overexpression of HABP1. Thus, the phenomenon of autophagy takes place prior to apoptosis induction in the HABP1 overexpressing cell line, F-HABP07.

p32 protein levels are integral to mitochondrial and endoplasmic reticulum morphology, cell metabolism and survival

p32 [also known as HABP1 (hyaluronan-binding protein 1), gC1qR (receptor for globular head domains complement 1q) or C1qbp (complement 1q-binding protein)] has been shown previously to have both mitochondrial and non-mitochondrial localization and functions. In the present study, we show for the first time that endogenous p32 protein is a mitochondrial protein in HeLa cells under control and stress conditions. In defining the impact of altering p32 levels in these cells, we demonstrate that the overexpression of p32 increased mitochondrial fibrils. Conversely, siRNA-mediated p32 knockdown enhanced mitochondrial fragmentation accompanied by a loss of detectable levels of the mitochondrial fusion mediator proteins Mfn (mitofusin) 1 and Mfn2. More detailed ultrastructure analysis by transmission electron microscopy revealed aberrant mitochondrial structures with less and/or fragmented cristae and reduced mitochondrial matrix density as well as more punctate ER (endoplasmic reticulum) with noticeable dissociation of their ribosomes. The analysis of mitochondrial bioenergetics showed significantly reduced capacities in basal respiration and oxidative ATP turnover following p32 depletion. Furthermore, siRNA-mediated p32 knockdown resulted in differential stress-dependent effects on cell death, with enhanced cell death observed in the presence of hyperosmotic stress or cisplatin treatment, but decreased cell death in the presence of arsenite. Taken together, our studies highlight the critical contributions of the p32 protein to the morphology of mitochondria and ER under normal cellular conditions, as well as important roles of the p32 protein in cellular metabolism and various stress responses.

Interactome analysis reveals that C1QBP (complement component 1, q subcomponent binding protein) is associated with cancer cell chemotaxis and metastasis

The complement component 1, q subcomponent binding protein (C1QBP/p32/HABP1) is a ubiquitously expressed and multicompartmental cellular protein involved in various biological processes. In order to further understand its biological functions, we conducted proteomics analysis of its interactome in this study. An improved sample preparation and mass spectrometric identification strategy was developed combining high-speed centrifugation, formaldehyde labeling, and two-dimensional reverse-phase liquid chromatography. Using this approach, we identified 187 interacting proteins and constructed a highly connected interacting network for C1QBP. Moreover, we explored the interaction between C1QBP and protein kinase C ζ, a key regulator of cell polarity and migration. The results indicated that C1QBP regulated the activity of protein kinase C ζ and modulated EGF-induced cancer cell chemotaxis. In addition, C1QBP was required for breast cancer metastasis in a severe combined immunodeficiency mouse model. Furthermore, C1QBP was observed to be overexpressed in breast cancer tissues, and its expression level was closely linked with distant metastasis and TNM stages. In summary, C1QBP was identified as a novel regulator of cancer metastasis that may serve as a therapeutic target for breast cancer treatment.

Bivariate Linkage between Acylation-Stimulating Protein and BMI and High-Density Lipoproteins

OBJECTIVE

Given the importance of visceral adiposity in the metabolic syndrome, whether levels of adipokines have shared genetic effects (pleiotropy) with aspects of the metabolic syndrome should be addressed. Acylation-stimulating protein (ASP), an adipose-derived protein, influences lipid metabolism, obesity, and glucose use. Therefore, our objective was to examine the genetic regulation of ASP and associated pleiotropic effects.

RESEARCH METHODS AND PROCEDURES

We assayed serum ASP levels in 435 Mexican Americans participating in the San Antonio Family Heart Study and performed univariate and bivariate variance components analysis.

RESULTS

Additive genetic heritability of ASP was 26% (p = 0.0004). Bivariate genetic analysis detected significant genetic correlations between ASP and several lipid measures but not between ASP and adiposity or diabetes measures. We detected two potential quantitative trait loci influencing ASP levels. The strongest signal was on chromosome 17 near marker D17S1303 [log of the odds ratio (LOD) = 2.7]. The signal on chromosome 15 reached its peak near marker D15S641 (LOD = 2.1). Both signals localize in regions reported to harbor quantitative trait loci influencing obesity and lipid phenotypes in this population. Bivariate linkage analysis yielded LODs of 4.7 for ASP and BMI on chromosome 17 and 3.2 for ASP and high-density lipoprotein2a on chromosome 15.

DISCUSSION

Given these findings, there seems to be a significant genetic contribution to variation in circulating levels of ASP and an interesting pattern of genetic correlation (i.e., pleiotropy) with other risk factors associated with the metabolic syndrome.

gC1qR expression in normal and pathologic human tissues: differential expression in tissues of epithelial and mesenchymal origin

The gC1qR (i.e., gC1q receptor, gC1q binding protein, p32, p33) is a multifunctional cellular protein that interacts with components of the complement, kinin, and coagulation cascades and select microbial pathogens. Enhanced gC1qR expression has been reported in adenocarcinomas arising in a variety of organs. The present study compared gC1qR expression in normal, inflammatory, dysplastic, and malignant tissue of epithelial and mesenchymal origin. gC1qR expression was visualized in tissue sections by immunohistochemistry using the 60.11 monoclonal antibody (i.e., IgG(1) mouse monoclonal antibody directed against gC1qR) and the UltraVision LP Detection System. Sections were counterstained with hematoxylin and examined by light microscopy. Strongest gC1qR expression was noted in epithelial tumors of breast, prostate, liver, lung, and colon, as well as in squamous and basal cell carcinoma of the skin. However, increased gC1qR staining was appreciated also in inflammatory and proliferative lesions of the same cell types, as well as in normal continuously dividing cells. In contrast, tumors of mesenchymal origin generally stained weakly, with the exception of osteoblasts, which stained in both benign and malignant tissues. The data suggest that increased gC1qR expression may be a marker of benign and pathologic cell proliferation, particularly in cells of epithelial origin, with potential diagnostic and therapeutic applications.

Significance of hyaluronan binding protein (HABP1/P32/gC1qR) expression in advanced serous ovarian cancer patients

BACKGROUND

To evaluate various risk factors related to the overall survival (OS) and progression free survival (PFS) in 131 patients with stage III-IV ovarian serous carcinoma.

METHODS

All patients underwent primary debulking surgery followed by a standard chemotherapeutic treatment regimen. Hyaluronan binding protein (HABP1) expression was evaluated using immunohistochemical-staining and assessed using western-immunoblotting analyses. A log-rank test was used to compare OS and PFS between cisplatin sensitive versus resistant patients. Multivariate analyses were used to identify risk factors associated with OS and PFS.

RESULTS

HABP1 over-expression was correlated to histological-differentiation, residual-tumor-size, serum CA-125 levels and International Federation of Gynecology and Obstetrics (FIGO) stage. Multivariate analyses demonstrated that increased expression of HABP1 was associated with cisplatin resistance. HABP1 low-expression resulted in an increased five-year OS and PFS. Cox proportional hazards test identified that high expression of HABP1 led to increased risk for stage III/IV serous ovarian cancer via poor OS and PFS. This was similar for cisplatin resistant patients. Thus, increased HABP1 immunoreactivity in ovarian cancer may lead to a shortening in disease-free intervals of patients.

CONCLUSION

HAPBP1 over-expression in primary ovarian carcinomas is related to a decrease in OS and PFS and may be utilized as a prognostic marker for stage III/IV patients.

Overexpression of hyaluronan-binding protein 1 (HABP1/p32/gC1qR) in HepG2 cells leads to increased hyaluronan synthesis and cell proliferation by up-regulation of cyclin D1 in AKT-dependent pathway

Overexpression of the mature form of hyaluronan-binding protein 1 (HABP1/gC1qR/p32), a ubiquitous multifunctional protein involved in cellular signaling, in normal murine fibroblast cells leads to enhanced generation of reactive oxygen species (ROS), mitochondrial dysfunction, and ultimately apoptosis with the release of cytochrome c. In the present study, human liver cancer cell line HepG2, having high intracellular antioxidant levels was chosen for stable overexpression of HABP1. The stable transformant of HepG2, overexpressing HABP1 does not lead to ROS generation, cellular stress, and apoptosis, rather it induced enhanced cell growth and proliferation over longer periods. Phenotypic changes in the stable transformant were associated with the increased "HA pool," formation of the "HA cable" structure, up-regulation of HA synthase-2, and CD44, a receptor for HA. Enhanced cell survival was further supported by activation of MAP kinase and AKT-mediated cell survival pathways, which leads to an increase in CYCLIN D1 promoter activity. Compared with its parent counterpart HepG2, the stable transformant showed enhanced tumorigenicity as evident by its sustained growth in low serum conditions, formation of the HA cable structure, increased anchorage-independent growth, and cell-cell adhesion. This study suggests that overexpression of HABP1 in HepG2 cells leads to enhanced cell survival and tumorigenicity by activating HA-mediated cell survival pathways.

Genetic analysis in Drosophila reveals a role for the mitochondrial protein p32 in synaptic transmission

Mitochondria located within neuronal presynaptic terminals have been shown to play important roles in the release of chemical neurotransmitters. In the present study, a genetic screen for synaptic transmission mutants of Drosophila has identified the first mutation in a Drosophila homolog of the mitochondrial protein P32. Although P32 is highly conserved and has been studied extensively, its physiological role in mitochondria remains unknown and it has not previously been implicated in neural function. The Drosophila P32 mutant, referred to as dp32^EC1, exhibited a temperature-sensitive (TS) paralytic behavioral phenotype. Moreover, electrophysiological analysis at adult neuromuscular synapses revealed a TS reduction in the amplitude of excitatory postsynaptic currents (EPSC) and indicated that dP32 functions in neurotransmitter release. These studies are the first to address P32 function in Drosophila and expand our knowledge of mitochondrial proteins contributing to synaptic transmission.

The role of TFAM-associated proteins in mitochondrial RNA metabolism

BACKGROUND

Mammalian mitochondrial DNA (mtDNA) takes on a higher structure called the nucleoid or mitochromosome, which corresponds to that of nuclear DNA. Mitochondrial transcription factor A (TFAM), which was cloned as a transcription factor for mitochondrial DNA, is critical for forming this higher structure and for maintenance of mtDNA.

SCOPE OF REVIEW

To investigate the functional aspects of the nucleoid, we have identified many RNA-binding proteins to be candidate TFAM interactors, including ERAL1 and p32.

MAJOR CONCLUSIONS

In this review, we would like to describe that ERAL1 binds to the mitochondrial rRNA component of the ribosomal small subunit and is an important constituent of this subunit. p32, which is involved in mitochondrial translation, may be a novel marker of clinical progression in prostate cancer. Here we describe these proteins, all of which are involved in translation within the mitochondrial matrix.

GENERAL SIGNIFICANCE

This review highlights the results from the mitochondrial nucleoid research in organic biochemistry. This article is part of a Special Issue entitled Biochemistry of Mitochondria.

Hyaluronan as an immune regulator in human diseases

Accumulation and turnover of extracellular matrix components are the hallmarks of tissue injury. Fragmented hyaluronan stimulates the expression of inflammatory genes by a variety of immune cells at the injury site. Hyaluronan binds to a number of cell surface proteins on various cell types. Hyaluronan fragments signal through both Toll-like receptor (TLR) 4 and TLR2 as well as CD44 to stimulate inflammatory genes in inflammatory cells. Hyaluronan is also present on the cell surface of epithelial cells and provides protection against tissue damage from the environment by interacting with TLR2 and TLR4. Hyaluronan and hyaluronan-binding proteins regulate inflammation, tissue injury, and repair through regulating inflammatory cell recruitment, release of inflammatory cytokines, and cell migration. This review focuses on the role of hyaluronan as an immune regulator in human diseases.

The molecular identity of the mitochondrial Ca2+ sequestration system

There is ample evidence to suggest that a dramatic decrease in mitochondrial Ca(2+) retention may contribute to the cell death associated with stroke, excitotoxicity, ischemia and reperfusion, and neurodegenerative diseases. Mitochondria from all studied tissues can accumulate and store Ca(2+) , but the maximum Ca(2+) storage capacity varies widely and exhibits striking tissue specificity. There is currently no explanation for this fact. Precipitation of Ca(2+) and phosphate in the mitochondrial matrix has been suggested to be the major form of storage of accumulated Ca(2+) in mitochondria. How this precipitate is formed is not known. The molecular identity of almost all proteins involved in Ca(2+) transport, storage and formation of the permeability transition pore is also unknown. This review summarizes studies aimed at identifying these proteins, and describes the properties of a known mitochondrial protein that may be involved in Ca(2+) transport and the structure of the permeability transition pore.

Identification of novel cell migration-promoting genes by a functional genetic screen

Here we describe the identification of novel cell migration-promoting genes based on an unbiased functional genetic screen in cultured cells. After the introduction of the retroviral mouse brain cDNA library into NIH3T3 mouse fibroblast cells, migration-promoted cells were selected by a 3-dimensional migration assay using cell culture inserts. After 5 rounds of enrichment, cDNAs were retrieved from the cells with a selected phenotype. Cell migration-promoting activity was confirmed by independent migration assays for the retrieved cDNAs, among which further investigation was focused on coiled-coil-helix-coiled-coil-helix domain-containing protein 2 (chchd2). Whereas overexpression of chchd2 promoted cell migration, knockdown of endogenous chchd2 expression reduced cell migration. Chchd2-induced cell migration was associated with augmented formation of actin stress fibers and focal adhesion, which was mediated through Akt, RhoA/ROCK, and Jnk pathways. CHCHD2 protein directly interacted with hyaluronic acid-binding protein 1 (HABP1) that possessed migration-suppressing activity. Intracellular localization and further functional studies suggested that CHCHD2 and HABP1 may mutually regulate each other to balance cell migration. Thus, chchd2 is a novel cell migration determinant identified by an in vitro functional genetic selection strategy. The selection method can also be useful for the isolation of genes that give other phenotypes of interest.

How do human cells react to the absence of mitochondrial DNA?

Background

Mitochondrial biogenesis is under the control of two different genetic systems: the nuclear genome (nDNA) and the mitochondrial genome (mtDNA). The mtDNA is a circular genome of 16.6 kb encoding 13 of the approximately 90 subunits that form the respiratory chain, the remaining ones being encoded by the nDNA. Eukaryotic cells are able to monitor and respond to changes in mitochondrial function through alterations in nuclear gene expression, a phenomenon first defined in yeast and known as retrograde regulation. To investigate how the cellular transcriptome is modified in response to the absence of mtDNA, we used Affymetrix HG-U133A GeneChip arrays to study the gene expression profile of two human cell lines, 143BTK⁻ and A549, which had been entirely depleted of mtDNA (ρ° cells), and compared it with that of corresponding undepleted parental cells (ρ⁺ cells).

Results

Our data indicate that absence of mtDNA is associated with: i) a down-regulation of cell cycle control genes and a reduction of cell replication rate, ii) a down-regulation of nuclear-encoded subunits of complex III of the respiratory chain and iii) a down-regulation of a gene described as the human homolog of ELAC2 of E. coli, which encodes a protein that we show to also target to the mitochondrial compartment.

Conclusions

Our results indicate a strong correlation between mitochondrial biogenesis and cell cycle control and suggest that some proteins could have a double role: for instance in controlling both cell cycle progression and mitochondrial functions. In addition, the finding that ELAC2 and maybe other transcripts that are located into mitochondria, are down-regulated in ρ° cells, make them good candidates for human disorders associated with defective replication and expression of mtDNA.

Mitochondrial/cell-surface protein p32/gC1qR as a molecular target in tumor cells and tumor stroma

A tumor homing peptide, LyP-1, selectively binds to tumor-associated lymphatic vessels and tumor cells in certain tumors and exhibits an antitumor effect. Here, we show that the protein known as p32 or gC1q receptor is the receptor for LyP-1. Various human tumor cell lines were positive for p32 expression in culture, and the expression was increased in xenograft tumors grown from the positive cell lines. Fluorescence-activated cell sorting analyses with anti-p32 antibodies showed that p32-positive cell lines expressed p32 at the cell surface. These cells bound and internalized LyP-1 peptide in proportion to the cell-surface expression level, which correlated with malignancy rather than total p32 expression in the cells. Like the LyP-1 peptide, p32 antibodies highlighted hypoxic areas in tumors, where they bound to both tumor cells and cells that expressed macrophage/myeloid cell markers and often seemed to be incorporated into the walls of tumor lymphatics. Significant p32 expression was common in human cancers and the p32 levels were often greatly elevated compared with the corresponding normal tissue. These results establish p32, particularly its cell-surface-expressed form, as a new marker of tumor cells and tumor-associated macrophages/myeloid cells in hypoxic/metabolically deprived areas of tumors. Its unique localization in tumors and its relative tumor specificity may make p32 a useful target in tumor diagnosis and therapy.

Higher expression of hyaluronan binding protein 1 (HABP1/p32/gC1qR/SF2) during follicular development and cumulus oocyte complex maturation in rat

Ovulation is a complex process of releasing a fertilizable oocyte and depends on the proper formation of an extracellular hyaluronan rich matrix by the cumulus oocyte complex (COC). The formation of a HA rich matrix is dependent on the synthesis and organization of HA in the presence of several biomolecules that mediate its crosslinking. To gain an insight into the follicular maturation and COC expansion, we have studied the expression of hyaluronan binding protein 1 (HABP1), which is known to interact specifically with hyaluronan. The level of HABP1 increased markedly during ovulation after gonadotropin stimulation, and the overexpression was seen in mural granulosa cells, expanding cumulus cells and follicular fluid. However, HABP1 could not be detected in the luteal cells of corpus luteum after ovulation. Such increased expression of HABP1 was observed both during in vivo and in vitro conditions of COC expansion. The level of HABP1 transcript was upregulated up to fivefold after COC expansion as compared to compact COC. Immunofluorescence analysis showed HABP1 to be localized in the cytoplasm and extracellular matrix, suggesting its role in ECM organization. The cultured expanded COC treated with hyaluronidase for different time periods showed the gradual dispersion of COC, which coincide with the loss of HABP1 from the matrix suggesting that HABP1 is bound to hyaluronan. These results indicate that HABP1 expressed in rat COCs during maturation may facilitate the formation of the HA matrix in the extracellular space around the oocyte with cumulus expansion during maturation.

The multifunctional protein GC1q-R interacts specifically with the i3 loop arginine cluster of the vasopressin V2 receptor

In this study, we identified the multifunctional protein GC1q-R as a novel vasopressin V(2) receptor (V(2)R) interacting protein. For this purpose, we have developed a proteomic approach combining pull-down assays using a cyclic peptide mimicking the third intracellular loop of V(2)R as a bait and mass spectrometry analyses of proteins isolated from either rat or human kidney tissues or the HEK 293 cell line. Co-immunoprecipitation of GC1q-R with the c-Myc-tagged h-V(2)R expressed in a HEK cell line confirmed the existence of a specific interaction between GC1q-R and the V(2) receptor. Then, construction of a mutant receptor in i3 loop allowed us to identify the i3 loop arginine cluster of the vasopressin V(2) receptor as the interacting determinant for GC1q-R interaction. Using purified receptor as a bait and recombinant (74-282) GC1q-R, we demonstrated a direct and specific interaction between these two proteins via the arginine cluster.

Excessive reactive oxygen species induces apoptosis in fibroblasts: role of mitochondrially accumulated hyaluronic acid binding protein 1 (HABP1/p32/gC1qR)

Constitutively expressed HABP1 in normal murine fibroblast cell line induces growth perturbation, morphological abnormalities along with initiation of apoptosis. Here, we demonstrate that though HABP1 accumulation started in mitochondria from 48 hr of growth, induction of apoptosis with the release of cytochrome c and apoptosome complex formation occurred only after 60 hr. This mitochondrial dysfunction was due to gradual increase in ROS generation in HABP1 overexpressing cells. Along with ROS generation, increased Ca 2+ influx in mitochondria leading to drop in membrane potential was evident. Interestingly, upon expression of HABP1, the respiratory chain complex I was shown to be significantly inhibited. Electronmicrograph confirmed defective mitochondrial ultrastructure. The reduction in oxidant generation and drop in apoptotic cell population accomplished by disruption of HABP1 expression, corroborating the fact that excess ROS generation in HABP1 overexpressing cells leading to apoptosis was due to mitochondrial HABP1 accumulation.

Upregulation of hyaluronan binding protein 1 (HABP1/p32/gC1qR) is associated with Cisplatin induced apoptosis

We have earlier reported that overexpression of HABP1 in fibroblast cells causes perturbed cell growth, extensive vacuolation and restricted entry to the S-phase, finally leading to apoptosis (Biochem Biophys Res Commun 2003; 300: 686-693). In the present study, we investigate the regulation of HABP1 expression in cisplatin induced apoptosis in HeLa cells. Apoptosis induced in HeLa cells at 24 h of cisplatin treatment was confirmed by nuclear fragmentation, increase in subdiploid population and the enhanced activation of ERK and upregulation of p53. In association with apoptosis induction, an upregulation of HABP1 expression was observed in HeLa cells at 18 and 24 h of cisplatin treatment. Quantification of HABP1 expression by flow cytometry confirmed a two-fold increase in total intracellular HABP1 expression at 24 h of cisplatin treatment. Under the same condition the HABP1 transcript level measured by semi quantitative RT PCR showed 2.5-fold increase ascertaining transcriptional regulation of HABP1 during cisplatin induced apoptosis. Further, in normal HeLa cells though a small amount of HABP1 can be detected in nucleus, but with apoptosis induction the protein is mainly concentrating around the nuclear periphery at 18 h of cisplatin treatment and is present both in the nucleus as well as in the cytosol at 24 h of treatment, suggesting its nuclear translocation during apoptosis. To substantiate our findings prior to the cisplatin treatment, the expression of HABP1 was reduced by small interfering RNA mediated knockdown. We observed a reduction in apoptotic cell population in cisplatin treated HeLa cells with disrupted HABP1 conferring resistance to cisplatin induced apoptosis. We report here that HABP1 upregulation in the cell is important for cisplatin induced apoptosis.

The extracellular signal-regulated kinase: multiple substrates regulate diverse cellular functions

The extracellular signal-regulated kinase (ERK) cascade is a central pathway that transmits signals from many extracellular agents to regulate cellular processes such as proliferation, differentiation and cell cycle progression. The signaling via the ERK cascade is mediated by sequential phosphorylation and activation of protein kinases in the different tiers of the cascade. Although the main core phosphorylation chain of the cascade includes Raf kinases, MEK1/2, ERK1/2 (ERKs) and RSKs, other alternatively spliced forms and distinct components exist in the different tiers, and participate in ERK signaling under specific conditions. These components enhance the complexity of the ERK cascade and thereby, enable the wide variety of functions that are regulated by it. Another factor that is important for the dissemination of ERKs' signals is the multiplicity of the cascade's substrates, which include transcription factors, protein kinases and phosphatases, cytoskeletal elements, regulators of apoptosis, and a variety of other signaling-related molecules. About 160 substrates have already been discovered for ERKs, and the list of these substrates, as well as the function and mechanism of activation of representative substrates, are described in the current review. Many of these substrates are localized in the nucleus, and seem to participate in the regulation of transcription upon stimulation. However, other substrates are found in the cytosol as well as in other cellular organelles, and those are responsible for processes such as translation, mitosis and apoptosis. Understanding of these processes may provide a full picture of the distinct, and even opposing cellular processes that are regulated by the ERK cascade.

Cellular p32 recruits cytomegalovirus kinase pUL97 to redistribute the nuclear lamina

Replication of human cytomegalovirus is limited at the level of nucleocytoplasmic transport of viral capsids, a process that requires the disassembly of the nuclear lamina. Deletion of the protein kinase gene UL97 from the viral genome showed that the activity of pUL97 plays an important role for viral capsid egress. Here, we report that p32, a novel cellular interactor of the viral kinase pUL97, promotes the accumulation of pUL97 at the nuclear membrane by recruiting the p32-pUL97 complex to the lamin B receptor. Transfection of active pUL97, but not a catalytically inactive mutant, induced a redistribution of lamina components as demonstrated for recombinant lamin B receptor-green fluorescent protein and endogenous lamins A and C. Consistent with this, p32 itself and lamins were phosphorylated by pUL97. Importantly, overexpression of p32 in human cytomegalovirus-infected cells resulted in increased efficiency of viral replication and release of viral particles. Thus, it is highly suggestive that the cellular protein p32 recruits pUL97 to induce a dissolution of the nuclear lamina thereby facilitating the nuclear export of viral capsids.

Hyaluronan catabolism: a new metabolic pathway

A new pathway of intermediary metabolism is described involving the catabolism of hyaluronan. The cell surface hyaluronan receptor, CD44, two hyaluronidases, Hyal-1 and Hyal-2, and two lysosomal enzymes, beta-glucuronidase and beta-N-acetylglucosaminidase, are involved. This metabolic cascade begins in lipid raft invaginations at the cell membrane surface. Degradation of the high-molecular-weight extracellular hyaluronan occurs in a series of discreet steps generating hyaluronan chains of decreasing sizes. The biological functions of the oligomers at each quantum step differ widely, from the space-filling, hydrating, anti-angiogenic, immunosuppressive 10(4)-kDa extracellular polymer, to 20-kDa intermediate polymers that are highly angiogenic, immuno-stimulatory, and inflammatory. This is followed by degradation to small oligomers that can induce heat shock proteins and that are anti-apoptotic. The single sugar products, glucuronic acid and a glucosamine derivative are released from lysosomes to the cytoplasm, where they become available for other metabolic cycles. There are 15 g of hyaluronan in the 70-kg individual, of which 5 g are cycled daily through this pathway. Some of the steps in this catabolic cascade can be commandeered by cancer cells in the process of growth, invasion, and metastatic spread.