Multifunctional activities of human fibroblast 34-kDa hyaluronic acid-binding protein

Clinically Relevant Biology of Hyaluronic Acid in the Desmoplastic Stroma of Pancreatic Ductal Adenocarcinoma

ABSTRACT

Pancreatic ductal adenocarcinoma (PDAC) is notorious for its poor outcome. The presence of a dense desmoplastic stroma is a hallmark of this malignancy, and abundant hyaluronic acid (HA) within this stroma is a common feature of PDAC. At the end of 2019, an HA-targeting drug, after initial promise, failed phase 3 clinical trials in PDAC. This failure in the face of such strong evidence for biological importance forces us to turn back to the research and seek a better understanding of HA biology in PDAC. Therefore, in this review, we reexamine what is known about HA biology, the methods used to detect and quantify HA, and the ability of the biological models in which HA has been investigated to recapitulate an HA-rich desmoplastic tumor stroma. The role of HA in PDAC relies on its complex interplay with a range of HA-associated molecules, which have not been as extensively investigated as HA itself. Therefore, using large genomic data sets, we cataloged the abundance and activity in PDAC of molecules that modulate HA synthesis, degradation, protein interactions, and receptor binding. Based on their association with clinical characteristics and individual patient outcomes, we suggest a small number of HA-associated molecules that warrant further investigation as biomarkers and drug targets.

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.

The role of CD44 in cancer chemoresistance: A concise review

CD44 is a cell surface adhesion molecule, which is overexpressed on cancer stem cells. The interaction of CD44 with hyaluronan is responsible for tumor development, metastasis, and expression of the chemoresistant phenotype. The overexpression of CD44 impedes the cytotoxic effect of chemotherapy medications in various cancers. Therefore, the high expression of CD44 is associated with a poor prognosis in affected patients. This high expression of CD44 in various cancers has provided an ample opportunity for the treatment of patients with chemoresistant malignancy. This review aims to demonstrate the various cross-talk between CD44 and intracellular and extracellular factors and highlight its role in developing chemoresistant tumors in some troublesome cancers.

High cytoplasm HABP1 expression as a predictor of poor survival and late tumor stage in pancreatic ductal adenocarcinoma patients

BACKGROUND

Hyaluronan-binding protein 1 (HABP1) overexpression has been confirmed in different malignancies and found to be strongly associated with tumor development and progression. The aim of the present study was to explore the impact of HABP1 in pancreatic ductal adenocarcinoma (PDAC) patients.

METHOD

HABP1 expression was evaluated in 89 PDAC specimens.

RESULTS

The expression of HABP1 was significantly higher in tumor tissues than that in adjacent normal tissues. High nucleus HABP1 expression and high cytoplasm HABP1 expression were both detected in PDAC tissues. Overall survival analysis by optical density showed that the mean survival was similar between patients with low and high optical density values of HABP1 expression (P = 0.312). The similar result was also found between patients with low-moderate or high nucleus HABP1 expression (P = 0.275). However, the mean survival was significantly poorer in patients with cytoplasm HABP1 overexpression (P < 0.001). High cytoplasm HABP1 expression was strongly correlated with late tumor stages, arterial involvement, lymph node metastasis and carbohydrate antigen 19-9 levels.

CONCLUSION

High cytoplasm HABP1 expression may prove to be a predictor of poor survival and late tumor stage in PDAC patients. HABP1 could serve as a promising biomarker to identify subsets of PDAC patients with high malignant clinical behavior.

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.

Elevated expression of hyaluronic acid binding protein 1 (HABP1)/P32/C1QBP is a novel indicator for lymph node and peritoneal metastasis of epithelial ovarian cancer patients

The present study aims to clarify whether hyaluronan binding protein 1 (HABP1/p32/C1QBP) is an indicator of peritoneal and lymph node metastasis in epithelial ovarian cancer (EOC), which to the authors' knowledge is not previously reported by others. Western blot analysis demonstrated that HABP1 was highly overexpressed in most metastatic lesions. Of 89 patients whose primary tumors showed high HABP1 expression on immunohistochemical staining, 85 (95.5%) presented peritoneal metastases and 43 (48.3%) had lymph node metastases. Univariate and multivariate logistic regression analyses revealed that HABP1 overexpression correlated with peritoneal dissemination and lymph node metastasis in EOC. The specificity and positive predictive value of HABP1 staining were shown to be better for peritoneal metastasis, while the negative and sensitivity predictive value of HABP1 staining were better for lymph node metastasis. The odds ratio of high versus low staining for peritoneal spread was 9.236 (95% confidence interval (CI), 2.705, 19.316), and that for lymph node metastasis was 8.614 (95% CI, 2.507, 21.039). Furthermore, HABP1 protein may potentially be used alone or in combination with other markers as a predictive marker of EOC patients with lymph node metastasis and/or peritoneal dissemination.

Mining the extracellular matrix for tissue engineering applications

Tissue engineering is a rapidly evolving interdisciplinary field that aims to regenerate new tissue to replace damaged tissues or organs. The extracellular matrix (ECM) of animal tissues is a complex mixture of macromolecules that play an essential instructional role in the development of tissues and organs. Therefore, tissue engineering approaches rely on the need to present the correct cues to cells, to guide them to maintain tissue-specific functions. Recent research efforts have allowed us to mine various sequences and motifs, which play key roles in these guidance functions, from the ECM. Small conserved peptide sequences mined from ECM molecules can mimic some of the biological functions of their large parent molecules. In addition, these peptide sequences can be linked to various biomaterial scaffolds that can provide the cells with mechanical support to ensure appropriate cell growth and aid the formation of the correct tissue structure. The tissue engineering field will continue to benefit from the advent of these mined ECM sequences which have two major advantages over recombinant ECM molecules: material consistency and scalability.

Increased expression of hyaluronic acid binding protein 1 is correlated with poor prognosis in patients with breast cancer

BACKGROUND AND OBJECTIVES

Hyaluronic acid binding protein 1 (HABP1), a family of proteins interacting with hyaluronan (HA), had been associated with cell adhesion and tumor invasion. The aim of this study was to investigate the correlation between clinicopathologic factors and patient survival time with the expression of HABP1 in breast cancer patients.

METHODS

Expression of HABP1 mRNA and protein were detected with real-time quantitative PCR and immunohistochemical staining in 63 breast cancer and non-cancerous matched tissues.

RESULTS

The mRNA expression level of HABP1 was unrelated to the patient's age, tumor size, histological grade, TNM stage. However, it proved to be positively related to axillary nodes metastasis (P = 0.008). Furthermore, it was shown that the survival rate of patients with low HABP1 expression was significantly higher than that of patients with high HABP1 expression (P = 0.025). Multivariate analysis revealed that HABP1 mRNA expression level was a significant factor for predicting prognosis (P = 0.022). The immunohistochemistry results showed that the expression level of HABP1 in breast cancer cells was higher than that in normal breast cells.

CONCLUSION

HABP1 might be an independent predictive factor for breast cancer prognosis and up-regulation of HABP1 might play an important role in the metastasis of breast cancer.

Protumorigenic role of HAPLN1 and its IgV domain in malignant pleural mesothelioma

PURPOSE

Tumor extracellular matrix (ECM) plays a crucial role in cancer progression mediating and transforming host-tumor interactions. Targeting the ECM is becoming an increasingly promising therapeutic approach in cancer treatment. We find that one of the ECM proteins, HAPLN1, is overexpressed in the majority of mesotheliomas. This study was designed to characterize the protumorigenic role of HAPLN1 in mesothelioma.

EXPERIMENTAL DESIGN

Overexpression of HAPLN1 was assessed and validated on a large set of normal/mesothelioma specimens on the RNA and protein levels. We also analyzed DNA copy number alterations in the HAPLN1 genomic locus using the array-based comparative genomic hybridization representational oligonucleotide microarray analysis tool. Tumorigenic activities of the HAPLN1 domains were evaluated in vitro on mesothelioma cells transfected with HAPLN1-expressing constructs.

RESULTS

We found that HAPLN1 is 23-fold overexpressed in stage I mesothelioma and confirmed it for 76% samples (n = 53) on RNA and 97% (n = 40) on protein levels. The majority of lung cancers showed no differential expression of HAPLN1. Analysis of DNA copy number alterations identified recurrent gain in the 5q14.3 HAPLN1 locus in approximately 27% of tumors. Noteworthy, high expression of HAPLN1 negatively correlated with time to progression (P = 0.05, log-rank test) and overall survival (P = 0.006). Proliferation, motility, invasion, and soft-agar colony formation assays on mesothelioma cells overexpressing full-length HAPLN1 or its functional domains strongly supported the protumorigenic role of HAPLN1 and its SP-IgV domain.

CONCLUSION

Overexpression of HAPLN1 and its SP-IgV domain increases tumorigenic properties of mesothelioma. Thus, targeting the SP-IgV domain may be one of the therapeutic approaches in cancer treatment.

The endothelial glycocalyx: composition, functions, and visualization

This review aims at presenting state-of-the-art knowledge on the composition and functions of the endothelial glycocalyx. The endothelial glycocalyx is a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Both endothelium- and plasma-derived soluble molecules integrate into this mesh. Over the past decade, insight has been gained into the role of the glycocalyx in vascular physiology and pathology, including mechanotransduction, hemostasis, signaling, and blood cell–vessel wall interactions. The contribution of the glycocalyx to diabetes, ischemia/reperfusion, and atherosclerosis is also reviewed. Experimental data from the micro- and macrocirculation alludes at a vasculoprotective role for the glycocalyx. Assessing this possible role of the endothelial glycocalyx requires reliable visualization of this delicate layer, which is a great challenge. An overview is given of the various ways in which the endothelial glycocalyx has been visualized up to now, including first data from two-photon microscopic imaging.

Hyaluronan-binding motif identified by panning a random peptide display library

The glycosaminoglycan hyaluronan (HA) is involved in a variety of functions such as cell migration, adhesion, activation of intracellular signaling, metastasis, inflammation and wound repair. These functions of HA are mediated via HA-binding proteins (HABPs). To derive details of the HA-binding site in HABPs, here, we panned a random peptide display library expressed on the E. coli flagellin protein using HA-coated plates. Using this random peptide display library, 40 positive clones were obtained and the nucleotide sequences were determined. As a result, an Arg-Arg sequence, in addition to the known B-X7-B motif, was found to bind to HA. A binding experiment using the IAsys resonant mirror biosensor verified that a peptide containing an Arg-Arg sequence binds to HA.

Receptor for the globular heads of C1q (gC1q-R, p33, hyaluronan-binding protein) is preferentially expressed by adenocarcinoma cells

Combinatorial Ig libraries with phage display allow in vitro generation of human Ig fragments without the need to maintain hybridomas in ongoing cell culture or to select circulating Ig from human serum. Identifying tumor-associated antigens on the surface of intact tumor cells, as opposed to purified proteins, presents a challenge due to the difficulty of preserving complex 3-D epitopic sites on the cell surface, the variable expression of antigens on different malignant cell types and the stereotactic interference of closely associated proteins on the intact membrane surface limiting accessibility to antigenic sites. A combinatorial Ig library of 10(10) clones was generated from the cDNA of PBMCs derived from patients with breast adenocarcinoma. Following subtractive panning, the library was enriched for Ig (Fab fragment) binding to intact adenocarcinoma cells and the resultant Fabs were screened against a cDNA expression library, itself generated from breast cancer cells. Using this approach, we isolated clones from the cDNA library expressing gC1q-R, a glycoprotein comprising the major structure of C1, the first component of the complement system. gC1q-R is a 33 kDa glycoprotein expressed not only on the cell surface but also intracellularly, with motifs that target it to mitochondria and complete homology with HABP and human HeLa cell protein p32, which is copurified with pre-mRNA SF2. Sequencing of the gene encoding tumor-associated gC1q-R did not reveal any consistent tumor-specific mutations. However, histochemical staining with anti-gC1q-R MAb demonstrated marked differential expression of gC1q-R in thyroid, colon, pancreatic, gastric, esophageal and lung adenocarcinomas compared to their nonmalignant histologic counterparts. In contrast, differential expression was not seen in endometrial, renal and prostate carcinomas. Despite high expression in breast carcinoma, gC1q-R was also expressed in nonmalignant breast tissue. Although the precise relation of gC1q-R to carcinogenesis remains unclear, our finding of tumor overexpression and the known multivalent binding of gC1q-R to not only C1q itself but also a variety of circulating plasma proteins as well as its involvement in cell-to-cell interactions suggest that gC1q-R may have a role in tumor metastases and potentially serve in molecule-specific targeting of malignant cells.

Sperm surface hyaluronan binding protein (HABP1) interacts with zona pellucida of water buffalo (Bubalus bubalis) through its clustered mannose residues

Sperm-oocyte interaction during fertilization is multiphasic, with multicomponent events, taking place between zona pellucida (ZP) glycoproteins and sperm surface receptor. d-mannosylated glycoproteins, the major constituents of ZP are considered to serve as ligands for sperm binding. The presence of hyaluronan binding protein 1 (HABP1) on sperm surface of different mammals including cattle and its possible involvement in sperm function is already reported. Recently, we have demonstrated the specificity of clustered mannose as another ligand for HABP1 (Kumar et al., 2001: J Biosci 26:325-332). Here, we report that only N-linked mannosylated zona-glycoproteins bind to sperm surface HABP1. Labeled HABP1 interacts with ZP of intact oocyte of Bubalus bubalis, which can be competed with unlabeled HABP1 or excess d-mannosylated albumin (DMA). This data suggests the specific interaction of HABP1 with ZP, through clustered mannose residues. In order to examine the physiological significance of such an interaction, the capacity of sperm binding to oocytes under in vitro fertilization plates was examined either in presence of DMA alone or in combination with HABP1. The number of sperms, bound to oocytes was observed to reduce significantly in presence of DMA, which could be reversed by the addition of purified recombinant HABP1 (rHABP1) in the same plate. This suggests that sperm surface HABP1 may act as mannose binding sites for zona recognition.

Constitutive expression of hyaluronan binding protein 1 (HABP1/p32/gC1qR) in normal fibroblast cells perturbs its growth characteristics and induces apoptosis

Hyaluronan binding protein 1 (HABP1) is a ubiquitously expressed multifunctional phospho-protein that interacts with a wide range of ligands and is implicated in cell signalling. Recently, we have reported that HABP1 is an endogenous substrate for MAP kinase and upon mitogenic stimulation it is translocated to the nucleus in a MAP kinase-dependent manner (Biochem. Biophys. Res. Commun. 291(4) (2002) 829-837). This prompted us to investigate the role of HABP1 in cell growth or otherwise in low MAP kinase background. We demonstrate that HABP1, when overexpressed in normal rat skin fibroblasts, remained in the cytosol, primarily concentrated around the nuclear periphery. However, HABP1 overexpressing cells showed extensive vacuolation and reduced growth rate, which was corrected by frequent medium replenishment. Further investigation revealed that HABP1 overexpressing cells undergo apoptosis, as detected by TUNEL assay, induction of Bax expression, and FACS analysis, and they failed to enter into the S-phase. Periodic medium supplementation prevented these cells from undergoing apoptotic death. We also demonstrate that upon induction of apoptosis in HeLa cells by cisplatin, HABP1 level is upregulated, indicating a correlation between HABP1 and cell death in a normal cellular environment.

Evidence for the presence of HABP1 pseudogene in multiple locations of mammalian genome

The gene encoding hyaluronan-binding protein 1 (HABP1) is expressed ubiquitously in different rat tissues, and is present in eukaryotic species from yeast to humans. Fluorescence in situ hybridization indicates that this is localized in human chromosome 17p13.3. Here, we report the presence of homologous sequences of HABP1 cDNA, termed processed HABP1 pseudogene in humans. This is concluded from an additional PCR product of ~0.5 kb, along with the expected band at approximately 5 kb as observed by PCR amplification of human genomic DNA with HABP1-specific primers. Partial sequencing of the 5-kb PCR product and comparison of the HABP1 cDNA with the sequence obtained from Genbank accession number AC004148 indicated that the HABP1 gene is comprised of six exons and five introns. The 0.5-kb additional PCR product was confirmed to be homologous to HABP1 cDNA by southern hybridization, sequencing, and by a sequence homology search. Search analysis with HABP1 cDNA sequence further revealed the presence of similar sequence in chromosomes 21 and 11, which could generate ~0.5 kb with the primers used. In this report, we describe the presence of several copies of the pseudogene of HABP1 spread over different chromosomes that vary in length and similarity to the HABP1 cDNA sequence. These are 1013 bp in chromosome 21 with 85.4% similarity, 1071 bp in chromosome 11 with 87.2% similarity, 818 bp in chromosome 15 with 82.3% similarity, and 323 bp in chromosome 4 with 84% similarity to HABP1 cDNA. We have also identified similar HABP1 pseudogenes in the rat and mouse genome. The human pseudogene sequence of HABP1 possesses a 10 base pair direct repeat of "AGAAAAATAA" in chromosome 21, a 12-bp direct repeat of "AG/CAAATTA/CAA/TTA" in chromosome 4, a 8-bp direct repeat of "ACAAAG/TCT" in chromosome 15. In the case of chromosome 11, there is an inverted repeat of "AGCCTGGGCGACAGAGCGAGA" ~50 bp upstream of the HABP1 pseudogene sequence. All of the HABP1 pseudogene sequences lack 5' promoter sequence and possess multiple mutations leading to the insertion of premature stop codons in all three reading frames. Rat and mouse homologs of the HABP1 pseudogene also contain multiple mutations, leading to the insertion of premature stop codons confirming the identity of a processed pseudogene.

Stage-specific expression of proprotein form of hyaluronan binding protein 1 (HABP1) during spermatogenesis in rat

The presence of the 34-kDa hyaluronan binding protein 1 (HABP1) on sperm surface and its role in fertilization is already established (Ranganathan et al., 1994: Mol Reprod Dev 38:69-76). In the present communication, we examined the expression of HABP1 in adult rat testis during spermatogenesis. Interestingly, using anti-rHABP1 antibody, we detected a protein of 55 kDa which was present only in testis, but not in other somatic tissues like spleen and liver. However, even in testis, only one transcript of HABP1 mRNA of 1.63 kb was observed. In addition, we confirm that this testis-specific 55 kDa protein was immunologically identical with proprotein form of HABP1 using antibody raised against a decapeptide present in the proprotein region of HABP1. Comparative immunohistochemistry of testis, spleen, and liver tissues using both the antibodies supported the observation that the proprotein form of HABP1 is present only in testis. Higher mRNA expression of HABP1 in testis as compared to that of liver and spleen could be speculated from the RT-PCR product. Finally, detailed study of the immunohistochemical staining of the seminiferous tubules revealed the expression of the HABP1 proprotein in specific stages of germ cells, like pachytene spermatocytes and round spermatids, but not in elongated ones, suggesting a possible role of HABP1 proprotein in spermatogenic differentiation.

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

The role of hyaluronan binding protein 1 (HABP1) in cell signaling was investigated and in vitro kinase assay demonstrated that it is a substrate for MAP kinase. Phosphorylation of endogenous HABP1 was also observed following treatment of J774 cells with PMA. HABP1 was coimmunoprecipitated with activated ERK, confirming their physical interaction in the cellular context. Upon PMA stimulation of normal rat fibroblast (F111) and transformed (HeLa) cells, the HABP1 level in the cytoplasm gradually decreased with a parallel increase in the nucleus. In HeLa cells, within 6 h of PMA treatment, HABP1 was completely translocated to the nucleus, which was prevented by PD98059, a selective inhibitor of ERK. We also observed that the nuclear translocation of HABP1 is concurrent with that of ERK, suggesting that ERK activation is a requirement for the translocation of HABP1. It is thus established for the first time that HABP1 is a substrate for ERK and an integral part of the MAP kinase cascade.

Disulfide bond formation through Cys186 facilitates functionally relevant dimerization of trimeric hyaluronan-binding protein 1 (HABP1)/p32/gC1qR

Hyaluronan-binding protein 1 (HABP1), a ubiquitous multifunctional protein, interacts with hyaluronan, globular head of complement component 1q (gC1q), and clustered mannose and has been shown to be involved in cell signalling. In vitro, this recombinant protein isolated from human fibroblast exists in different oligomeric forms, as is evident from the results of various independent techniques in near-physiological conditions. As shown by size-exclusion chromatography under various conditions and glutaraldehyde cross-linking, HABP1 exists as a noncovalently associated trimer in equilibrium with a small fraction of a covalently linked dimer of trimers, i.e. a hexamer. The formation of a covalently-linked hexamer of HABP1 through Cys186 as a dimer of trimers is achieved by thiol group oxidation, which can be blocked by modification of Cys186. The gradual structural transition caused by cysteine-mediated disulfide linkage is evident as the fluorescence intensity increases with increasing Hg(2+) concentration until all the HABP1 trimer is converted into hexamer. In order to understand the functional implication of these transitions, we examined the affinity of the hexamer for different ligands. The hexamer shows enhanced affinity for hyaluronan, gC1q, and mannosylated BSA compared with the trimeric form. Our data, analyzed with reference to the HABP1/p32 crystal structure, suggest that the oligomerization state and the compactness of its structure are factors that regulate its function.

Reduction in the level of hyaluronan binding protein 1 (HABP1) is associated with loss of sperm motility

Hyaluronan binding protein 1 (HABP1) was reported to be present on human sperm surface and its involvement in fertilization has already been elucidated (Mol. Repro. Dev. 38 (1994) 69). In the present communication, we report a significant reduction in the level of this protein in sperms from asthenozoospermic and oligozoospermic patients as compared to normozoospermic one. Further evidence of the absence of HABP1 in sperms, having motility <20% is documented, which again is a determining factor for fertilization. HABP1 was quantitatively determined using anti-HABP1 antibody from sperm extracts isolated from semen samples of both the fertile and infertile groups demonstrating low sperm motility. Sperm samples with low motility revealed a significant reduction in the level of HABP1 in immunoblot detection as well as immunolocalization experiment. It suggests that decreased HABP1 level may be associated with low motility of sperms, which in turn might cause infertility in the patient. Thus, the sperm surface HABP1 level can be correlated with the degree of sperm motility, an important criteria for fertilization.

Evidence for clustered mannose as a new ligand for hyaluronan- binding protein (HABP1) from human fibroblasts

We have earlier reported that overexpression of the gene encoding human hyaluronan-binding protein (HABP1) is functionally active, as it binds specifically with hyaluronan (HA). In this communication, we confirm the collapse of the filamentous and branched structure of HA by interaction with increasing concentrations of recombinant-HABP1 (rHABP1). HA is the reported ligand of rHABP1. Here, we show the affinity of rHABP1 towards D-mannosylated albumin (DMA) by overlay assay and purification using a DMA affinity column. Our data suggests that DMA is another ligand for HABP1. Furthermore, we have observed that DMA inhibits the binding of HA in a concentration-dependent manner, suggesting its multiligand affinity amongst carbohydrates. rHABP1 shows differential affinity towards HA and DMA which depends on pH and ionic strength. These data suggest that affinity of rHABP1 towards different ligands is regulated by the microenvironment.

Hyaluronan: a multifunctional, megaDalton, stealth molecule

Hyaluronan has been implicated in biological processes such as cell adhesion, migration and proliferation. Traditionally, it was thought to be associated with the extracellular matrix, but, hyaluronan may also have unimagined roles inside the cell. Investigation of hyaluronan synthesis and degradation, the identification of new receptors and binding proteins, and the elucidation of hyaluronan-dependent signaling pathways are providing novel insights into the true biological functions of this fascinating molecule.

Staphylococcus aureus protein A recognizes platelet gC1qR/p33: a novel mechanism for staphylococcal interactions with platelets

The adhesion of Staphylococcus aureus to platelets is a major determinant of virulence in the pathogenesis of endocarditis. Molecular mechanisms mediating S. aureus interactions with platelets, however, are incompletely understood. The present study describes the interaction between S. aureus protein A and gC1qR/p33, a multifunctional, ubiquitously distributed cellular protein, initially described as a binding site for the globular heads of C1q. Suspensions of fixed S. aureus or purified protein A, chemically cross-linked to agarose support beads, were found to capture native gC1qR from whole platelets. Moreover, biotinylated protein A bound specifically to fixed, adherent, human platelets. This interaction was inhibited by unlabeled protein A, soluble recombinant gC1qR (rgC1qR), or anti-gC1qR antibody F(ab')(2) fragments. The interaction between protein A and platelet gC1qR was underscored by studies illustrating preferential recognition of the protein A-bearing S. aureus Cowan I strain by gC1qR compared to recognition of the protein A-deficient Wood 46 strain, as well as inhibition of S. aureus Cowan I strain adhesion to immobilized platelets by soluble protein A. Further characterization of the protein A-gC1qR interaction by solid-phase enzyme-linked immunosorbent assay techniques measuring biotinylated gC1qR binding to immobilized protein A revealed specific binding that was inhibited by soluble protein A with a 50% inhibitory concentration of (3.3 +/- 0.7) x 10(-7) M (mean +/- standard deviation; n = 3). Rabbit immunoglobulin G (IgG) also prevented gC1qR-protein A interactions, and inactivation of protein A tyrosil residues by hyperiodination, previously reported to prevent the binding of IgG Fc, but not Fab, domains to protein A, abrogated gC1qR binding. These results suggest similar protein A structural requirements for gC1qR and IgG Fc binding. Further studies of structure and function using a truncated gC1qR mutant lacking amino acids 74 to 95 demonstrated that the protein A binding domain lies outside of the gC1qR amino-terminal alpha helix, which contains binding sites for the globular heads of C1q. In conclusion, the data implicate the platelet gC1qR as a novel cellular binding site for staphylococcal protein A and suggest an additional mechanism for bacterial cell adhesion to sites of vascular injury and thrombosis.

Cytokeratin 1 and gC1qR mediate high molecular weight kininogen binding to endothelial cells

High molecular weight kininogen (HK) attaches to endothelial cells by separate sites on the heavy and light chains and requires 15-50 microM zinc. Previously identified binding proteins include gC1qR, cytokeratin 1, and the urokinase plasminogen activator receptor; however, their relative contributions to binding are not yet clarified. We have prepared affinity columns to which were coupled either cleaved HK or peptide LDCNAEVYVVPWEKKIYPTVNCQPLGM derived from heavy-chain domain 3. Endothelial cell membranes were solubilized and chromatographed in the presence or absence of zinc ion, the bound proteins were eluted, and active fractions were identified by dot blot using biotinylated HK, SDS/PAGE, and Western blot analysis. The peptide containing column eluate revealed but one band at 68 kDa if zinc ion was present which was identified as cytokeratin 1 by amino acid sequencing of an internal peptide. The HK affinity column revealed bands at 68 kDa (cytokeratin 1), 33 kDa (gC1qR), and 66 kDa (unidentified). HK or domain 3-derived peptide bound to the 68 kDa band; prekallikrein and Factor XII did not. HK or Factor XII bound to the 33-kDa band if zinc was present while no binding to the 66 kDa band was observed. Antibody to cytokeratin 1 inhibited HK binding to endothelial cells by 30%, antibody to gC1qR inhibited HK binding to endothelial cells by 72%, and a mixture of both inhibited binding by 86%. Our data suggest HK binding by interaction of the heavy-chain domain 3 with cytokeratin 1 and the light chain with gC1qR.

Rapid hyaluronan uptake is associated with enhanced motility: implications for an intracellular mode of action

Texas red-labeled hyaluronan (TR-HA) is rapidly taken up in a CD44 independent manner into ras-transformed 10T1/2 fibroblasts, where it accumulates in both cell ruffles/lamellae, the perinuclear area, and the nucleus. HA does not accumulate in the cell ruffles/lamellae of parental 10T1/2 cells. Addition of HA to ras-transformed cells promotes their random motility but has no effect on 10T1/2 cell motility. 10T1/2 cells can be modified to take up HA into cell ruffles by exposure to phorbol ester or direct microinjection of HA into cells. Both treatments significantly stimulate 10T1/2 cell motility.

Regulation of cellular phosphorylation of hyaluronan binding protein and its role in the formation of second messenger

The presence of the 34-kDa hyaluronan binding protein, a new member of the 'hyaladherins' family, was demonstrated in a wide variety of cell lines by immunoblot analysis. This protein was observed to be highly phosphorylated in transformed fibroblasts compared to normal fibroblasts. Phosphorylation was enhanced in the presence of its ligand i.e., hyaluronan, but not in the presence of other glycosaminoglycans. The phosphorylated form of this hyaluronan binding protein was shown to be present on the cell surface and could be detected in serum-free medium. The regulation of the cellular and cell surface phosphorylation of HA-binding protein by HA, PMA and calyculin-A was demonstrated in different cell lines. Hyaluronan enhanced the phosphorylation of PLC-gamma in association with increased formation of inositol 1,4,5-triphosphate, both of which were specifically blocked by pretreatment of the cells with purified anti-hyaluronan binding protein antibodies. The data presented here indicate a role for the 34-kDa hyaluronan binding protein in cellular signal transduction.