Formation of the 67-kDa laminin receptor by acylation of the precursor

Vitamin E functions by association with a novel binding site on the 67 kDa laminin receptor activating diacylglycerol kinase

It is generally recognized that the main function of α-tocopherol (αToc), which is the most active form of vitamin E, is its antioxidant effect, while non-antioxidant effects have also been reported. We previously found that αToc ameliorates diabetic nephropathy via diacylglycerol kinase alpha (DGKα) activation in vivo, and the activation was not related to the antioxidant effect. However, the underlying mechanism of how αToc activates DGKα have been enigmatic. We report that the membrane-bound 67 kDa laminin receptor (67LR), which has previously been shown to serve as a receptor for epigallocatechin gallate (EGCG), also contains a novel binding site for vitamin E, and its association with Vitamin E mediates DGKα activation by αToc. We employed hydrogen-deuterium exchange mass spectrometry (HDX/MS) and molecular dynamics (MD) simulations to identify the specific binding site of αToc on the 67LR and discovered the conformation of the specific hydrophobic pocket that accommodates αToc. Also, HDX/MS and MD simulations demonstrated the detailed binding of EGCG to a water-exposed hydrophilic site on 67LR, while in contrast αToc binds to a distinct hydrophobic site. We demonstrated that 67LR triggers an important signaling pathway mediating non-antioxidant effects of αToc, such as DGKα activation. This is the first evidence demonstrating a membrane receptor for αToc and one of the underlying mechanisms of a non-antioxidant function for αToc.

Laminin Receptor-Mediated Nanoparticle Uptake by Tumor Cells: Interplay of Epigallocatechin Gallate and Magnetic Force at Nano–Bio Interface

Epigallocatechin gallate (EGCG), a major tea catechin, enhances cellular uptake of magnetic nanoparticles (MNPs), but the mechanism remains unclear. Since EGCG may interact with the 67-kDa laminin receptor (67LR) and epidermal growth factor receptor (EGFR), we investigate whether a receptor and its downstream signaling may mediate EGCG’s enhancement effects on nanoparticle uptake. As measured using a colorimetric iron assay, EGCG induced a concentration-dependent enhancement effect of MNP internalization by LN-229 glioma cells, which was synergistically enhanced by the application of a magnetic field. Transmission electron microscopy demonstrated that EGCG increased the number, but not the size, of internalized vesicles, whereas EGCG and the magnet synergistically increased the size of vesicles. EGCG appears to enhance particle–particle interaction and thus aggregation following a 5-min magnet application. An antibody against 67LR, knockdown of 67LR, and a 67LR peptide (amino acid 161–170 of 67LR) attenuated EGCG-induced MNP uptake by 35%, 100%, and 45%, respectively, suggesting a crucial role of 67LR in the effects of EGCG. Heparin, the 67LR-binding glycosaminoglycan, attenuated EGCG-induced MNP uptake in the absence, but not presence, of the magnet. Such enhancement effects of EGCG were attenuated by LY294002 (a phosphoinositide 3-kinase inhibitor) and Akt inhibitor, but not by agents affecting cGMP levels, suggesting potential involvement of signaling downstream of 67LR. In contrast, the antibody against EGFR exerted no effect on EGCG-enhanced internalization. These results suggest that 67LR may be potentially amenable to tumor-targeted therapeutics.

Changes in subcellular localization of Lysyl-tRNA synthetase and the 67-kDa laminin receptor in epithelial ovarian cancer metastases

BACKGROUND: Although lysyl-tRNA synthetase (KARS1) is predominantly located in the cytosol, it is also present in the plasma membrane where it stabilizes the 67-kDa laminin receptor (67LR). This physical interaction is strongly increased under metastatic conditions. However, the dynamic interaction of these two proteins and the turnover of KARS1 in the plasma membrane has not previously been investigated. OBJECTIVE: Our objective in this study was to identify the membranous location of KARS1 and 67LR and investigate if this changes with the developmental stage of epithelial ovarian cancer (EOC) and treatment with the inhibitor BC-K01. In addition, we evaluated the therapeutic efficacy of BC-K01 in combination with paclitaxel, as the latter is frequently used to treat patients with EOC. METHODS: Overall survival and prognostic significance were determined in EOC patients according to KARS1 and 67LR expression levels as determined by immunohistochemistry. Changes in the location and expression of KARS1 and 67LR were investigated in vitro after BC-K01 treatment. The effects of this compound on tumor growth and apoptosis were evaluated both in vitro and in vivo. RESULTS: EOC patients with high KARS1 and high 67LR expression had lower progression-free survival rates than those with low expression levels of these two markers. BC-K01 reduced cell viability and increased apoptosis in combination with paclitaxel in EOC cell xenograft mouse models. BC-K01 decreased membranous KARS1 expression, causing a reduction in 67LR membrane expression in EOC cell lines. BC-K01 significantly decreased in vivo tumor weight and number of nodules, especially when used in combination with paclitaxel. CONCLUSIONS: Co-localization of KARS1 and 67LR in the plasma membrane contributes to EOC progression. Inhibition of the KARS1-67LR interaction by BC-K01 suppresses metastasis in EOC.

Epigallocatechine-3-gallate Inhibits the Adipogenesis of Human Mesenchymal Stem Cells via the Regulation of Protein Phosphatase-2A and Myosin Phosphatase

Epigallocatechin-3-gallate (EGCG) has widespread effects on adipocyte development. However, the molecular mechanisms of EGCG are not fully understood. We investigate the adipogenic differentiation of human-derived mesenchymal stem cells, including lipid deposition and changes in the expression and phosphorylation of key transcription factors, myosin, protein phosphatase-2A (PP2A), and myosin phosphatase (MP). On day 6 of adipogenic differentiation, EGCG (1–20 µM) suppressed lipid droplet formation, which was counteracted by an EGCG-binding peptide for the 67 kDa laminin receptor (67LR), suggesting that EGCG acts via 67LR. EGCG decreased the phosphorylation of CCAAT-enhancer-binding protein beta via the activation of PP2A in a protein kinase A (PKA)-dependent manner, leading to the partial suppression of peroxisome proliferator-activated receptor gamma (PPARγ) and adiponectin expression. Differentiated cells exhibited a rounded shape, cortical actin filaments, and lipid accumulation. The EGCG treatment induced cell elongation, stress fiber formation, and less lipid accumulation. These effects were accompanied by the degradation of the MP target subunit-1 and increased the phosphorylation of the 20 kDa myosin light chain. Our results suggest that EGCG acts as an agonist of 67LR to inhibit adipogenesis via the activation of PP2A and suppression of MP. These events are coupled with the decreased phosphorylation and expression levels of adipogenic transcription factors and changes in cell shape, culminating in curtailed adipogenesis.

Rpsa Signaling Regulates Cortical Neuronal Morphogenesis via Its Ligand, PEDF, and Plasma Membrane Interaction Partner, Itga6

Neuromorphological defects underlie neurodevelopmental disorders and functional defects. We identified a function for Rpsa in regulating neuromorphogenesis using in utero electroporation to knockdown Rpsa, resulting in apical dendrite misorientation, fewer/shorter extensions, and decreased spine density with altered spine morphology in upper neuronal layers and decreased arborization in upper/lower cortical layers. Rpsa knockdown disrupts multiple aspects of cortical development, including radial glial cell fiber morphology and neuronal layering. We investigated Rpsa's ligand, PEDF, and interacting partner on the plasma membrane, Itga6. Rpsa, PEDF, and Itga6 knockdown cause similar phenotypes, with Rpsa and Itga6 overexpression rescuing morphological defects in PEDF-deficient neurons in vivo. Additionally, Itga6 overexpression increases and stabilizes Rpsa expression on the plasma membrane. GCaMP6s was used to functionally analyze Rpsa knockdown via ex vivo calcium imaging. Rpsa-deficient neurons showed less fluctuation in fluorescence intensity, suggesting defective subthreshold calcium signaling. The Serpinf1 gene coding for PEDF is localized at chromosome 17p13.3, which is deleted in patients with the neurodevelopmental disorder Miller-Dieker syndrome. Our study identifies a role for Rpsa in early cortical development and for PEDF-Rpsa-Itga6 signaling in neuromorphogenesis, thus implicating these molecules in the etiology of neurodevelopmental disorders like Miller-Dieker syndrome and identifying them as potential therapeutics.

The mechanisms of ameliorating effect of a green tea polyphenol on diabetic nephropathy based on diacylglycerol kinase α

Significant efforts have been made to ameliorate diabetic nephropathy (DN) by inhibiting protein kinase C. However, these efforts have not been successful in human trials, suggesting that novel therapeutic strategies are required. Thus far, it has been reported that green tea polyphenol epigallocatechin gallate (EGCg) improved albuminuria in DN in a human trial. Our previous study revealed that activation of diacylglycerol kinase α (DGKα) plays a crucial role in the amelioration of DN and that EGCg activates DGKα. Here, we investigated whether and how DGKα contributes to the amelioration of DN upon stimulation by EGCg by using streptozotocin-induced type 1 diabetic model mice. Our results revealed that EGCg ameliorated albuminuria in DN through DGKα in vivo, and methylated EGCg, which has higher absorption in the plasma improved albuminuria in DN effectively. Additionally, we showed that c-Src mediated EGCg-induced DGKα translocation and colocalized with the 67 kDa laminin receptor, which is an EGCg receptor. Furthermore, EGCg attenuated the loss of podocytes in DN by preventing a decrease in focal adhesion under high glucose conditions. Our results indicate that the DGKα pathway is an attractive therapeutic target and that activating this pathway is a novel strategy for treating DN.

37/67-laminin receptor facilitates neural crest cell migration during enteric nervous system development

Enteric nervous system (ENS) development is governed by interactions between neural crest cells (NCC) and the extracellular matrix (ECM). Hirschsprung disease (HSCR) results from incomplete NCC migration and failure to form an appropriate ENS. Prior studies implicate abnormal ECM in NCC migration failure. We performed a comparative microarray of the embryonic distal hindgut of wild-type and EdnrB^NCC-/- mice that model HSCR and identified laminin-β1 as upregulated in EdnrB^NCC-/- colon. We identified decreased expression of 37/67 kDa laminin receptor (LAMR), which binds laminin-β1, in human HSCR myenteric plexus and EdnrB^NCC-/- NCC. Using a combination of in vitro gut slice cultures and ex vivo organ cultures, we determined the mechanistic role of LAMR in NCC migration. We found that enteric NCC express LAMR, which is downregulated in human and murine HSCR. Binding of LAMR by the laminin-β1 analog YIGSR promotes NCC migration. Silencing of LAMR abrogated these effects. Finally, applying YIGSR to E13.5 EdnrB^NCC-/- colon explants resulted in 80%-100% colonization of the hindgut. This study adds LAMR to the large list of receptors through which NCC interact with their environment during ENS development. These results should be used to inform ongoing integrative, regenerative medicine approaches to HSCR.

siRNA - Mediated LRP/LR knock-down reduces cellular viability of malignant melanoma cells through the activation of apoptotic caspases

The 37 kDa/67 kDa laminin receptor (LRP/LR) is over-expressed in tumor cells and has been implicated in several tumourigenic processes such as metastasis and telomerase activation, however, more importantly the focus of the present study is on the maintenance of cellular viability and the evasion of apoptosis. The aim of the study was to investigate the role of LRP/LR on the cellular viability of early (A375) and late stage (A375SM) malignant melanoma cells. Flow cytometry and western blot analysis revealed that A375SM cells contain more cell-surface and total LRP/LR levels in comparison to the A375 cells, respectively. In order to determine the effect of LRP/LR on cell viability and apoptosis, LRP was down-regulated via siRNA technology. MTT assays revealed that LRP knock-down led to significant reductions in the viability of A375 and A375SM cells. Confocal microscopy indicated nuclear morphological changes suggestive of apoptotic induction in both cell lines and Annexin-V FITC/PI assays confirmed this observation. Additionally, caspase-3 activity assays revealed that apoptosis was induced in both cell lines after siRNA-mediated down-regulation of LRP. Caspase-8 and -9 activity assays suggested that post LRP knock-down; A375 cells undergo apoptosis solely via the extrinsic pathway, while A375SM cells undergo apoptosis via the intrinsic pathway.

IMPLICATIONS

siRNAs mediated LRP knock-down might represent a powerful alternative therapeutic strategy for the treatment of malignant melanoma through the induction of apoptosis.

A dock derived compound against laminin receptor (37 LR) exhibits anti-cancer properties in a prostate cancer cell line model

Laminin receptor (67 LR) is a 67 kDa protein derived from a 37 kDa precursor (37 LR). 37/67 LR is a strong clinical correlate for progression, aggression, and chemotherapeutic relapse of several cancers including breast, prostate, and colon. The ability of 37/67 LR to promote cancer cell aggressiveness is further increased by its ability to transduce physiochemical and mechanosensing signals in endothelial cells and modulate angiogenesis. Recently, it was demonstrated that 37/67 LR modulates the anti-angiogenic potential of the secreted glycoprotein pigment epithelium-derived factor (PEDF). Restoration of PEDF balance is a desirable therapeutic outcome, and we sought to identify a small molecule that could recapitulate known signaling properties of PEDF but without the additional complications of peptide formulation or gene delivery safety validation. We used an in silico drug discovery approach to target the interaction interface between PEDF and 37 LR. Following cell based counter screening and binding validation, we characterized a hit compound's anti-viability, activation of PEDF signaling-related genes, anti-wound healing, and anti-cancer signaling properties. This hit compound has potential for future development as a lead compound for treating tumor growth and inhibiting angiogenesis.

Anti-LRP/LR-specific antibody IgG1-iS18 impedes adhesion and invasion of pancreatic cancer and neuroblastoma cells

BACKGROUND

Cancer has become a global burden due to its high incidence and mortality rates, with an estimated 14.1 million cancer cases reported worldwide in 2012 particularly as a result of metastasis. Metastasis involves two crucial steps: adhesion and invasion, and the non-integrin receptor; the 37-kDa/67-kDa laminin receptor precursor/ high affinity laminin receptor (LRP/LR) has been shown to be overexpressed on the surface of tumorigenic cells, thus being implicated in the enhancement of these two crucial steps. The current study investigated the role of LRP/LR on the aggressiveness of pancreatic cancer (AsPC-1) and neuroblastoma (IMR-32) cells with respect to their adhesive and invasive potential.

METHODS

AsPC-1 and IMR-32 cells were utilized as the experimental cell lines for the study. Cell surface LRP/LR levels were visualised and quantified on the experimental and control (MCF-7) cell lines via confocal microscopy and flow cytometry, respectively. Total LRP/LR levels in the cell lines were assessed by Western blotting and the adhesive and invasive potential of the above-mentioned cell lines was determined before and after supplementation with the anti-LRP/LR specific antibody IgG1-iS18. Statistical significance of the data was confirmed via the use of the two-tailed student's t-test and Pearson's correlation coefficient.

RESULTS

Flow cytometry revealed that AsPC-1 and IMR-32 cells displayed significantly higher cell surface LRP/LR levels in comparison to the MCF-7 control cell line. However, Western blotting and subsequent densitometric analysis revealed that all three tumorigenic cell lines displayed no significant difference in total LRP/LR levels. The treatment of AsPC-1 and IMR-32 cells with IgG1-iS18 caused a significant reduction in the adhesive and invasive potential of the cells to laminin-1 and through the ECM-like Matrigel™, respectively. Pearson's correlation coefficients indicated a high correlation, thus suggesting a directly proportional relationship between cell surface LRP/LR levels and the adhesive and invasive potential of AsPC-1 and IMR-32 cells.

CONCLUSION

These findings suggest that through the interference of the LRP/LR-laminin-1 interaction, the anti-LRP/LR specific antibody IgG1-iS18 may act as an alternative therapeutic tool for the treatment of metastatic pancreatic cancer and neuroblastoma.

Function of membranous lysyl-tRNA synthetase and its implication for tumorigenesis

Aminoacyl-tRNA synthetases (ARSs) are essential enzymes that conjugate specific amino acids to their cognate tRNAs for protein synthesis. Besides their catalytic activity, recent studies have uncovered many additional functions of these enzymes through their interactions with diverse cellular factors. Among human ARSs, cytosolic lysyl-tRNA synthetase (KRS) is often highly expressed in cancer cells and tissues, and facilitates cancer cell migration and invasion through the interaction with the 67kDa laminin receptor on the plasma membrane. Specific modulation of this interaction by small molecule inhibitors has revealed a new way to control metastasis. Here, we summarize the pro-metastatic functions of KRS and their patho-physiological implications.

The Transition of the 37-Kda Laminin Receptor (Rpsa) to Higher Molecular Weight Species: Sumoylation or Artifact?

The 37-kDa laminin receptor (37LRP or RPSA) is a remarkable, multifaceted protein that functions in processes ranging from matrix adhesion to ribosome biogenesis. Its ability to engage extracellular laminin is further thought to contribute to cellular migration and invasion. Most commonly associated with metastatic cancer, RPSA is also increasingly found to be important in other pathologies, including microbial infection, neurodegenerative disease and developmental malformations. Importantly, it is thought to have higher molecular weight forms, including a 67-kDa species (67LR), the expression of which is linked to strong laminin binding and metastatic behavior. The composition of these larger forms has remained elusive and controversial. Homo- and heterodimerization have been proposed as events capable of building the larger species from the monomeric 37-kDa precursor, but solid evidence is lacking. Here, we present data suggesting that higher molecular weight species require SUMOylation to form. We also comment on the difficulty of isolating larger RPSA species for unambiguous identification and demonstrate that cell lines stably expressing tagged RPSA for long periods of time fail to produce tagged higher molecular weight RPSA. It is possible that higher molecular weight species like 67LR are not derived from RPSA.

The 37/67 kDa laminin receptor (LR) inhibitor, NSC47924, affects 37/67 kDa LR cell surface localization and interaction with the cellular prion protein

The 37/67 kDa laminin receptor (LR) is a non-integrin protein, which binds both laminin-1 of the extracellular matrix and prion proteins, that hold a central role in prion diseases. The 37/67 kDa LR has been identified as interactor for the prion protein (PrP(C)) and to be required for pathological PrP (PrP(Sc)) propagation in scrapie-infected neuronal cells, leading to the possibility that 37/67 kDa LR-PrP(C) interaction is related to the pathogenesis of prion diseases. A relationship between 37/67 kDa LR and PrP(C) in the presence of specific LR inhibitor compounds has not been investigated yet. We have characterized the trafficking of 37/67 kDa LR in both neuronal and non-neuronal cells, finding the receptor on the cell surface and nuclei, and identified the 67 kDa LR as the almost exclusive isoform interacting with PrP(C). Here, we show that the treatment with the 37/67 kDa LR inhibitor, NSC47924, affects both the direct 37/67 kDa LR-PrP(C) interaction in vitro and the formation of the immunocomplex in live cells, inducing a progressive internalization of 37/67 kDa LR and stabilization of PrP(C) on the cell surface. These data reveal NSC47924 as a useful tool to regulate PrP(C) and 37/67 kDa LR trafficking and degradation, representing a novel small molecule to be tested against prion diseases.

Monoclonal antibodies specific for oncofetal antigen--immature laminin receptor protein: Effects on tumor growth and spread in two murine models

The oncofetal antigen - immature laminin receptor protein (OFA/iLRP) has been linked to metastatic tumor spread for several years. The present study, in which 2 highly-specific, high-affinity OFA/iLRP-reactive mouse monoclonal antibodies were examined for ability to suppress tumor cell growth and metastatic spread in the A20 B-cell leukemia model and the B16 melanoma model, provides the first direct evidence that targeting OFA/iLRP with exogenous antibodies can have therapeutic benefit. While the antibodies were modestly effective at preventing tumor growth at the primary injection site, both antibodies strongly suppressed end-organ tumor formation following intravenous tumor cell injection. Capacity of anti-OFA/iLRP antibodies to suppress tumor spread through the blood in the leukemia model suggests their use as a therapy for individuals with leukemic disease (either for patients in remission or even as part of an induction therapy). The results also suggest use against metastatic spread with solid tumors.

Deciphering the complex three-way interaction between the non-integrin laminin receptor, galectin-3 and Neisseria meningitidis

The non-integrin laminin receptor (LAMR1/RPSA) and galectin-3 (Gal-3) are multi-functional host molecules with roles in diverse pathological processes, particularly of infectious or oncogenic origins. Using bimolecular fluorescence complementation and confocal imaging, we demonstrate that the two proteins homo- and heterodimerize, and that each isotype forms a distinct cell surface population. We present evidence that the 37 kDa form of LAMR1 (37LRP) is the precursor of the previously described 67 kDa laminin receptor (67LR), whereas the heterodimer represents an entity that is distinct from this molecule. Site-directed mutagenesis confirmed that the single cysteine (C(173)) of Gal-3 or lysine (K(166)) of LAMR1 are critical for heterodimerization. Recombinant Gal-3, expressed in normally Gal-3-deficient N2a cells, dimerized with endogenous LAMR1 and led to a significantly increased number of internalized bacteria (Neisseria meningitidis), confirming the role of Gal-3 in bacterial invasion. Contact-dependent cross-linking determined that, in common with LAMR1, Gal-3 binds the meningococcal secretin PilQ, in addition to the major pilin PilE. This study adds significant new mechanistic insights into the bacterial-host cell interaction by clarifying the nature, role and bacterial ligands of LAMR1 and Gal-3 isotypes during colonization.

Looking into laminin receptor: critical discussion regarding the non-integrin 37/67-kDa laminin receptor/RPSA protein

The 37/67-kDa laminin receptor (LAMR/RPSA) was originally identified as a 67-kDa binding protein for laminin, an extracellular matrix glycoprotein that provides cellular adhesion to the basement membrane. LAMR has evolutionary origins, however, as a 37-kDa RPS2 family ribosomal component. Expressed in all domains of life, RPS2 proteins have been shown to have remarkably diverse physiological roles that vary across species. Contributing to laminin binding, ribosome biogenesis, cytoskeletal organization, and nuclear functions, this protein governs critical cellular processes including growth, survival, migration, protein synthesis, development, and differentiation. Unsurprisingly given its purview, LAMR has been associated with metastatic cancer, neurodegenerative disease and developmental abnormalities. Functioning in a receptor capacity, this protein also confers susceptibility to bacterial and viral infection. LAMR is clearly a molecule of consequence in human disease, directly mediating pathological events that make it a prime target for therapeutic interventions. Despite decades of research, there are still a large number of open questions regarding the cellular biology of LAMR, the nature of its ability to bind laminin, the function of its intrinsically disordered C-terminal region and its conversion from 37 to 67 kDa. This review attempts to convey an in-depth description of the complexity surrounding this multifaceted protein across functional, structural and pathological aspects.

Oncofetal antigen/immature laminin receptor protein in pregnancy and cancer

The 37-kDa immature laminin receptor protein (iLRP) is a speciesconserved, universal immunogenic protein that is expressed in all thus-far examined embryonic and early fetal cells of inbred and outbred rodents. It has also been identified in human concepti. It is altered through normal maturation processes to become a non-immunogenic 67-kDa dimeric mature laminin receptor protein (mLRP) in mid-to late gestation in the mammalian fetus. This antigen ceases to be expressed as an active autoimmunogen in the full-term fetus and in the normal differentiating tissues and organs of the neonate or adult organism, apparently due to dimerization, but it is re-expressed as an immunogenic monomer in tumor cells. In this review, we highlight the known mechanisms of immune responses with particular emphasis on the possible role of the 37-kDa oncofetal antigen/immature laminin receptor (OFA/iLRP) in both pregnancy and cancer.

Anti-LRP/LR specific antibody IgG1-iS18 impedes adhesion and invasion of liver cancer cells

Two key events, namely adhesion and invasion, are pivotal to the occurrence of metastasis. Importantly, the 37 kDa/67 kDa laminin receptor (LRP/LR) has been implicated in enhancing these two events thus facilitating cancer progression. In the current study, the role of LRP/LR in the adhesion and invasion of liver cancer (HUH-7) and leukaemia (K562) cells was investigated. Flow cytometry revealed that the HUH-7 cells displayed significantly higher cell surface LRP/LR levels compared to the poorly-invasive breast cancer (MCF-7) control cells, whilst the K562 cells displayed significantly lower cell surface LRP/LR levels in comparison to the MCF-7 control cells. However, Western blotting and densitometric analysis revealed that all three tumorigenic cell lines did not differ significantly with regards to total LRP/LR levels. Furthermore, treatment of liver cancer cells with anti-LRP/LR specific antibody IgG1-iS18 (0.2 mg/ml) significantly reduced the adhesive potential of cells to laminin-1 and the invasive potential of cells through the ECM-like Matrigel, whilst leukaemia cells showed no significant differences in both instances. Additionally, Pearson's correlation coefficients suggested direct proportionality between cell surface LRP/LR levels and the adhesive and invasive potential of liver cancer and leukaemia cells. These findings suggest the potential use of anti-LRP/LR specific antibody IgG1-iS18 as an alternative therapeutic tool for metastatic liver cancer through impediment of the LRP/LR- laminin-1 interaction.

The protein expression profile in hepatopancreas of scallop Chlamys farreri under heat stress and Vibrio anguillarum challenge

Heat stress and pathogen infection have been considered as the main causes for mass mortality of cultured scallops during summer. In the present study, the expression profiles of proteins in the hepatopancreas of scallop Chlamys farreri were examined to reveal the possible mechanisms of physiological responses of scallop beneath heat stress and bacterial infection. An earlier occurred and higher mortality was observed in the scallops from combination treated group (28 °C and an injection of Vibrio anguillarum) in comparison to those in heat stress (28 °C) and bacteria challenge (V. anguillarum injection only) group, as well as control (PBS) and blank (untreated) group. The proteins in the hepatopancreas from scallops post 6 h of treatment were analyzed by using 2-D PAGE and ImageMaster 2D Platinum. There were total 1003 spots detected in control group, 1193 spots in heat stress group, 1263 spots in bacteria challenge group, and 1241 spots in the combination group. Fifteen protein spots expressed differentially between the combination treatment group and the bacteria challenge group were successfully identified by mass spectrometry and they were mainly classified as binding and catalytic proteins, such as endoglucanase, methylmalonate-semialdehyde dehydrogenase, xylose isomerase, tryptophanyl-tRNA synthetase, 40s ribosomal protein SA, glutathione S-transferase 4, and Mitochondrial transcription factor A, etc. These results indicated that the mortality of scallops suffered from the combination treatment was probably attributed to the impaired modulation of digestion and metabolism and ruined protein synthesis caused by heat stress together with bacteria infection. These data also provided valuable insights into the possible mechanisms of summer mortality occurrence of scallop at protein level.

Laminin receptor 37/67LR regulates adhesion and proliferation of normal human intestinal epithelial cells

Interactions between the cell basal membrane domain and the basement membrane are involved in several cell functions including proliferation, migration and differentiation. Intestinal epithelial cells can interact with laminin, a major intestinal basement membrane glycoprotein, via several cell-surface laminin-binding proteins including integrin and non-integrin receptors. The 37/67kDa laminin receptor (37/67LR) is one of these but its role in normal epithelial cells is still unknown. The aim of this study was to characterise the expression pattern and determine the main function of 37/67LR in the normal human small intestinal epithelium. Immunolocalization studies revealed that 37/67LR was predominantly present in the undifferentiated/proliferative region of the human intestinal crypt in both the immature and adult intestine. Using a human intestinal epithelial crypt (HIEC) cell line as experimental model, we determined that 37/67LR was expressed in proliferative cells in both the cytoplasmic and membrane compartments. Small-interfering RNA-mediated reduction of 37/67LR expression led to HIEC cell-cycle reduction and loss of the ability to adhere to laminin-related peptides under conditions not altering ribosomal function. Taken together, these findings indicate that 37/67LR regulates proliferation and adhesion in normal intestinal epithelial cells independently of its known association with ribosomal function.

Laminin receptor 1: a novel protein interacting with human circadian clock protein, hPer1

The circadian clock is the central timing system that controls numerous physiologic processes. The current model of these oscillators is based on autoregulatory transcription and translation feedback loops of these circadian genes in which Period1 (Per1) gene occupies a central position. The laminin receptor 1 (Lamr1) and its precursor are expressed in most tissues and play important roles in several physiologic and pathologic processes, including cell differentiation, growth, migration and cancer invasion. The present study showed that Lamr1 was a novel protein that interacted with human circadian clock protein hPer1 by the yeast two-hybrid system and co-immunoprecipitation, which was expressed in many tissues and did not display circadian rhythm. The expression of hPer1 was knocked down to 84.9% by the hPer1 RNA interfering test, but the expression levels of Lamr1 was not depressed by the hPer1 RNA interfering test. The results suggest that Lamr1 is a novel protein that interacts with human circadian clock protein hPer1 and Lamr1 is not a direct efferent element of circadian clock.

Downregulation of the non-integrin laminin receptor reduces cellular viability by inducing apoptosis in lung and cervical cancer cells

The non-integrin laminin receptor, here designated the 37-kDa/67-kDa laminin receptor (LRP/LR), is involved in many physiologically relevant processes, as well as numerous pathological conditions. The overexpression of LRP/LR on various cancerous cell lines plays critical roles in tumour metastasis and angiogenesis. This study investigated whether LRP/LR is implicated in the maintenance of cellular viability in lung and cervical cancer cell lines. Here we show a significant reduction in cellular viability in the aforementioned cell lines as a result of the siRNA-mediated downregulation of LRP. This reduction in cellular viability is due to increased apoptotic processes, reflected by the loss of nuclear integrity and the significant increase in the activity of caspase-3. These results indicate that LRP/LR is involved in the maintenance of cellular viability in tumorigenic lung and cervix uteri cells through the blockage of apoptosis. Knockdown of LRP/LR by siRNA might represent an alternative therapeutic strategy for the treatment of lung and cervical cancer.

The folded and disordered domains of human ribosomal protein SA have both idiosyncratic and shared functions as membrane receptors

The human RPSA [ribosomal protein SA; also known as LamR1(laminin receptor 1)] belongs to the ribosome but is also a membrane receptor for laminin, growth factors, prion, pathogens and the anticarcinogen EGCG (epigallocatechin-gallate). It contributes to the crossing of the blood–brain barrier by neurotropic viruses and bacteria, and is a biomarker of metastasis. RPSA includes an N-terminal domain, which is folded and homologous to the prokaryotic RPS2, and a C-terminal extension, which is intrinsically disordered and conserved in vertebrates. We used recombinant derivatives of RPSA and its N- and C-domains to quantify its interactions with ligands by in-vitro immunochemical and spectrofluorimetric methods. Both N- and C-domains bound laminin with K_D (dissociation constants) of 300 nM. Heparin bound only to the N-domain and competed for binding to laminin with the negatively charged C-domain, which therefore mimicked heparin. EGCG bound only to the N-domain with a K_D of 100 nM. Domain 3 of the envelope protein from yellow fever virus and serotypes-1 and -2 of dengue virus bound preferentially to the C-domain whereas that from West Nile virus bound only to the N-domain. Our quantitative in-vitro approach should help clarify the mechanisms of action of RPSA, and ultimately fight against cancer and infectious agents.

The potential roles of a laminin receptor in adhesion and apoptosis of cells of the marine bivalve Meretrix meretrix

Background

The laminin receptors (LRs) play important roles in cell adhesion to the extracellular matrix, certain cell-cell adhesions, and the activation of many intracellular signaling pathways. Studies of LRs have primarily focused on mammals, while few studies of LRs in marine invertebrates have been reported. The functions of LRs in marine bivalve species are still unclear.

Methodology/Principal Findings

In this study, we cloned and sequenced an LR gene, MmeLR, from the clam Meretrix meretrix. The MmeLR mRNA and protein detected by realtime PCR and western blots were primarily distributed in muscle tissues. Far-western analysis showed a specific interaction between recombinant MmeLR and the LR ligand laminin. The results of the binding assay suggested a role of LR in cell adhesion and apoptosis in cultured primary cells of mantle tissues from M. meretrix. The Bcl-2 mRNA expression level in primary cells cultured in matrigel (mainly laminin) coated plates was significantly higher than in cells cultured in non-coated plates at 48 h of culture, while the p53 mRNA expression pattern was inversely related to that of bcl-2, suggesting that MmeLR is involved in p53-dependent apoptosis, and the binding between MmeLR and laminin inhibits apoptosis during primary cell culture.

Conclusions

Our results suggest that MmeLR may be involved in cell adhesion and apoptosis. This study may increase the understanding of the role of laminin receptor in cell adhesion and apoptosis and help to improve the culture of primary cells of marine invertebrates.

Comprehensive proteomic analysis of nonintegrin laminin receptor interacting proteins

Human nonintegrin laminin receptor is a multifunctional protein acting as an integral component of the ribosome and a cell surface receptor for laminin-1. The laminin receptor is overexpressed in several human cancers and is also the cell surface receptor for several viruses and pathogenic prion proteins, making it a pathologically significant protein. This study focused on the proteomic characterization of laminin receptor interacting proteins from Mus musculus. The use of affinity chromatography with immobilized recombinant laminin receptor coupled with mass spectrometry analysis identified 45 proteins with high confidence. Following validation through coimmunoprecipitation, the proteins were classified based on predicted function into ribosomal, RNA processing, signal transduction/metabolism, protein processing, cytoskeleton/cell anchorage, DNA/chromatin, and unknown functions. A significant portion of the identified proteins is related to functions or localizations previously described for laminin receptor. This work represents a comprehensive proteomic approach to studying laminin receptor and provides an essential stepping stone to a better mechanistic understanding of this protein's diverse functions.

Mapping the laminin receptor binding domains of Neisseria meningitidis PorA and Haemophilus influenzae OmpP2

Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae are major bacterial agents of meningitis. They each bind the 37/67-kDa laminin receptor (LamR) via the surface protein adhesins: meningococcal PilQ and PorA, H. influenzae OmpP2 and pneumococcal CbpA. We have previously reported that a surface-exposed loop of the R2 domain of CbpA mediates LamR-binding. Here we have identified the LamR-binding regions of PorA and OmpP2. Using truncated recombinant proteins we show that binding is dependent on amino acids 171-240 and 91-99 of PorA and OmpP2, respectively, which are predicted to localize to the fourth and second surface-exposed loops, respectively, of these proteins. Synthetic peptides corresponding to the loops bound LamR and could block LamR-binding to bacterial ligands in a dose dependant manner. Meningococci expressing PorA lacking the apex of loop 4 and H. influenzae expressing OmpP2 lacking the apex of loop 2 showed significantly reduced LamR binding. Since both loops are hyper-variable, our data may suggest a molecular basis for the range of LamR-binding capabilities previously reported among different meningococcal and H. influenzae strains.

Inhibition of metastasis by HEXIM1 through effects on cell invasion and angiogenesis

We report on the role of hexamethylene-bis-acetamide-inducible protein 1 (HEXIM1) as an inhibitor of metastasis. HEXIM1 expression is decreased in human metastatic breast cancers when compared with matched primary breast tumors. Similarly we observed decreased expression of HEXIM1 in lung metastasis when compared with primary mammary tumors in a mouse model of metastatic breast cancer, the polyoma middle T antigen (PyMT) transgenic mouse. Re-expression of HEXIM1 (through transgene expression or localized delivery of a small molecule inducer of HEXIM1 expression, hexamethylene-bis-acetamide) in PyMT mice resulted in inhibition of metastasis to the lung. Our present studies indicate that HEXIM1 downregulation of HIF(-)1α protein allows not only for inhibition of vascular endothelial growth factor-regulated angiogenesis, but also for inhibition of compensatory pro-angiogenic pathways and recruitment of bone marrow-derived cells (BMDCs). Another novel finding is that HEXIM1 inhibits cell migration and invasion that can be partly attributed to decreased membrane localization of the 67 kDa laminin receptor, 67LR, and inhibition of the functional interaction of 67LR with laminin. Thus, HEXIM1 re-expression in breast cancer has therapeutic advantages by simultaneously targeting more than one pathway involved in angiogenesis and metastasis. Our results also support the potential for HEXIM1 to indirectly act on multiple cell types to suppress metastatic cancer.

Green tea polyphenol EGCG sensing motif on the 67-kDa laminin receptor

Background

We previously identified the 67-kDa laminin receptor (67LR) as the cell-surface receptor conferring the major green tea polyphenol (–)-epigallocatechin-3-O-gallate (EGCG) responsiveness to cancer cells. However, the underlying mechanism for interaction between EGCG and 67LR remains unclear. In this study, we investigated the possible role of EGCG-67LR interaction responsible for its bioactivities.

Methodology/Principal Findings

We synthesized various peptides deduced from the extracellular domain corresponding to the 102-295 region of human 67LR encoding a 295-amino acid. The neutralizing activity of these peptides toward EGCG cell-surface binding and inhibition of cancer cell growth were assayed. Both activities were inhibited by a peptide containing the 10-amino acid residues, IPCNNKGAHS, corresponding to residues 161-170. Furthermore, mass spectrometric analysis revealed the formation of a EGCG-LR161-170 peptide complex. A study of the amino acid deletion/replacement of the peptide LR161-170 indicated that the 10-amino acid length and two basic amino acids, K¹⁶⁶ and H¹⁶⁹, have a critical role in neutralizing EGCG’s activities. Moreover, neutralizing activity against the anti-proliferation action of EGCG was observed in a recombinant protein of the extracellular domain of 67LR, and this effect was abrogated by a deletion of residues 161-170. These findings support that the 10 amino-acid sequence, IPCNNKGAHS, might be the functional domain responsible for the anti-cancer activity of EGCG.

Conclusions/Significance

Overall, our results highlight the nature of the EGCG-67LR interaction and provide novel structural insights into the understanding of 67LR-mediated functions of EGCG, and could aid in the development of potential anti-cancer compounds for chemopreventive or therapeutic uses that can mimic EGCG-67LR interactions.

Extraribosomal functions associated with the C terminus of the 37/67 kDa laminin receptor are required for maintaining cell viability

The 37/67 kDa laminin receptor (LAMR) is a multifunctional protein, acting as an extracellular receptor, localizing to the nucleus, and playing roles in rRNA processing and ribosome assembly. LAMR is important for cell viability; however, it is unclear which of its functions are essential. We developed a silent mutant LAMR construct, resistant to siRNA, to rescue the phenotypic effects of knocking down endogenous LAMR, which include inhibition of protein synthesis, cell cycle arrest, and apoptosis. In addition, we generated a C-terminal-truncated silent mutant LAMR construct structurally homologous to the Archaeoglobus fulgidus S2 ribosomal protein and missing the C-terminal 75 residues of LAMR, which displays more sequence divergence. We found that HT1080 cells stably expressing either silent mutant LAMR construct still undergo arrest in the G₁ phase of the cell cycle when treated with siRNA. However, the expression of full-length silent mutant LAMR rescues cell viability, whereas the expression of the C-terminal-truncated LAMR does not. Interestingly, we also found that both silent mutant constructs restore protein translation and localize to the nucleus. Our findings indicate that the ability of LAMR to regulate viability is associated with its C-terminal 75 residues. Furthermore, this function is distinct from its role in cell proliferation, independent of its ribosomal functions, and may be regulated by a nonnuclear localization.

Interactions between laminin receptor and the cytoskeleton during translation and cell motility

Human laminin receptor acts as both a component of the 40S ribosomal subunit to mediate cellular translation and as a cell surface receptor that interacts with components of the extracellular matrix. Due to its role as the cell surface receptor for several viruses and its overexpression in several types of cancer, laminin receptor is a pathologically significant protein. Previous studies have determined that ribosomes are associated with components of the cytoskeleton, however the specific ribosomal component(s) responsible has not been determined. Our studies show that laminin receptor binds directly to tubulin. Through the use of siRNA and cytoskeletal inhibitors we demonstrate that laminin receptor acts as a tethering protein, holding the ribosome to tubulin, which is integral to cellular translation. Our studies also show that laminin receptor is capable of binding directly to actin. Through the use of siRNA and cytoskeletal inhibitors we have shown that this laminin receptor-actin interaction is critical for cell migration. These data indicate that interactions between laminin receptor and the cytoskeleton are vital in mediating two processes that are intimately linked to cancer, cellular translation and migration.

Green tea polyphenol sensing

Green tea polyphenols have emerged over the past two decades as an important dietary factor for health promotion. There is considerable evidence that tea polyphenols, in particular (-)-epigallocatechin-3-gallate (EGCG) inhibit carcinogenesis. However, the mechanisms for the cancer-preventive activity of EGCG are not completely characterized and many features remain to be elucidated. Recently we have identified a cell-surface EGCG receptor and the relating molecules that confer EGCG responsiveness to many cancer cells at physiological concentrations. Here, we review some of the reported mechanisms for the cancer chemopreventive action of EGCG and provide an overview of several molecules that sense and manage the physiological functions of EGCG.

Structure-guided identification of a laminin binding site on the laminin receptor precursor

The 37/ 67-kDa human laminin receptor (LamR) is a cell surface receptor for laminin, prion protein, and a variety of viruses. Because of its wide range of ligands, LamR plays a role in numerous pathologies. LamR overexpression correlates with a highly invasive cell phenotype and increased metastatic ability, mediated by interactions between LamR and laminin. In addition, the specific targeting of LamR with small interfering RNAs, blocking antibodies, and Sindbis viral vectors confers anti-tumor effects. We adopted a structure-based approach to map a laminin binding site on human LamR by comparing the sequences and crystal structures of LamR and Archaeoglobus fulgidus S2p, a non-laminin-binding ortholog. Here, we identify a laminin binding site on LamR, comprising residues Phe32, Glu35, and Arg155, which are conserved among mammalian species. Mutation of these residues results in a significant loss of laminin binding. Further, recombinant wild-type LamR is able to act as a soluble decoy to inhibit cellular migration towards laminin. Mutation of this laminin binding site results in loss of migration inhibition, which demonstrates the physiological role of Phe32, Glu35, and Arg155 for laminin binding activity. Mapping of the LamR binding site should contribute to the development of therapeutics that inhibit LamR interactions with laminin and may aid in the prevention of tumor growth and metastasis.

The adaptor protein LAD/TSAd mediates laminin-dependent T cell migration via association with the 67 kDa laminin binding protein

The adaptor protein, LAD/TSAd, plays essential roles in T cell activation. To further understand the functions of this protein, we performed yeast two-hybrid screening using TSAd as bait and identified 67 kDa laminin binding protein (LBP) as the interacting partner. Subsequently, TSAd-LBP interaction was confirmed in D1.1 T cell line. Upon costimulation by T cell receptor (TCR) plus laminin crosslinking or TCR plus integrin alpha6 crosslinking, LBP was coimmunoprecipitated with TSAd. Moreover, TCR plus laminin costimulation-dependent T cell migration was enhanced in D1.1 T cells overexpressing TSAd but was disrupted in D1.1 cells overexpressing dominant negative form of TSAd or TSAd shRNA. These data show that, upon TCR plus integrin costimulation, TSAd associates with LBP and mediates T lymphocyte migration.

O-GlcNAc cycling enzymes associate with the translational machinery and modify core ribosomal proteins

At least 20 core ribosome proteins are modified by O-GlcNAc. O-GlcNAcase is localized to the nucleolus and O-GlcNAc transferase is excluded from the nucleolus. Both enzymes associate with active polysomes. Overexpression of OGT disrupts ribosomal subunit homeostasis. Data suggest that O-GlcNAc regulates translation and ribosome biogenesis.

Protein synthesis is globally regulated through posttranslational modifications of initiation and elongation factors. Recent high-throughput studies have identified translation factors and ribosomal proteins (RPs) as substrates for the O-GlcNAc modification. Here we determine the extent and abundance of O-GlcNAcylated proteins in translational preparations. O-GlcNAc is present on many proteins that form active polysomes. We identify twenty O-GlcNAcylated core RPs, of which eight are newly reported. We map sites of O-GlcNAc modification on four RPs (L6, L29, L32, and L36). RPS6, a component of the mammalian target of rapamycin (mTOR) signaling pathway, follows different dynamics of O-GlcNAcylation than nutrient-induced phosphorylation. We also show that both O-GlcNAc cycling enzymes OGT and OGAse strongly associate with cytosolic ribosomes. Immunofluorescence experiments demonstrate that OGAse is present uniformly throughout the nucleus, whereas OGT is excluded from the nucleolus. Moreover, nucleolar stress only alters OGAse nuclear staining, but not OGT staining. Lastly, adenovirus-mediated overexpression of OGT, but not of OGAse or GFP control, causes an accumulation of 60S subunits and 80S monosomes. Our results not only establish that O-GlcNAcylation extensively modifies RPs, but also suggest that O-GlcNAc play important roles in regulating translation and ribosome biogenesis.

Tissue-dependent induction of apoptosis by matrix metalloproteinase stromelysin-3 during amphibian metamorphosis

Matrix metalloproteinases (MMPs) are a superfamily of Zn(2+)-dependent proteases that are capable of cleaving the proteinaceous component of the extracellular matrix (ECM). The ECM is a critical medium for cell-cell interactions and can also directly signal cells through cell surface ECM receptors, such as integrins. In addition, many growth factors and signaling molecules are stored in the ECM. Thus, ECM remodeling and/or degradation by MMPs are expected to affect cell fate and behavior during many developmental and pathological processes. Numerous studies have shown that the expression of MMP mRNAs and proteins associates tightly with diverse developmental and pathological processes, such as tumor metastasis and mammary gland involution. In vivo evidence to support the roles of MMPs in these processes has been much harder to get. Here, we will review some of our studies on MMP11, or stromelysin-3, during the thyroid hormone-dependent amphibian metamorphosis, a process that resembles the so-called postembryonic development in mammals (from a few months before to several months after birth in humans when organ growth and maturation take place). Our investigations demonstrate that stromelysin-3 controls apoptosis in different tissues via at least two distinct mechanisms.

Expression of Galectin-3 in renal neoplasms: a diagnostic, possible prognostic marker

CONTEXT

Galectin-3, a member of the lectin family, was shown to be expressed in normal distal tubular cells and in renal cell carcinomas (RCC). However, its diagnostic and prognostic significance in RCC is as yet undefined.

OBJECTIVES

To describe the expression of Galectin-3 among different histologic subtypes of renal neoplasms and to determine their diagnostic and prognostic significances.

DESIGN

The expression of Galectin-3 was evaluated in 217 renal neoplasms by tissue microarray and immunohistochemistry with semiquantitative analysis.

RESULTS

Strong expression of Galectin-3 was observed in 92 of 217 of renal neoplasms (42.4%). Although 22 of 23 oncocytomas (95.7%) and 19 of 21 chromophobe RCCs (90.5%) express Galectin-3, only 4 of 32 papillary RCCs (12.5%) and 47 of 137 clear cell RCCs (34.3%) express Galectin-3, suggesting that it may be used as a potential diagnostic marker. Galectin-3 expression was seen in 55% of high-grade (Fuhrman nuclear grades 3 and 4) versus 21% low-grade (grades 1 and 2) clear cell RCCs (P < .001).

CONCLUSIONS

This study confirms that Galactin-3 is strongly overexpressed in renal cell neoplasms of distal tubular differentiation, that is, oncocytoma and chromophobe RCCs, suggesting it might be used as a possible differential diagnostic tool for renal cell neoplasm with oncocytic or granular cells. Furthermore, we observed a strong association of overexpression of Galectin-3 and high nuclear grade in clear cell RCC. These results also suggest a possible pivotal role for Galectin-3 in the differentiation and prognosis of clear cell RCC.

Upregulation in rat spinal cord microglia of the nonintegrin laminin receptor 37 kDa-LRP following activation by a traumatic lesion or peripheral injury

The molecular mechanisms triggering microglial activation after injury to the central nervous system, involving cell-extracellular matrix interactions and cytokine signaling, are not yet fully understood. Here, we report that resident microglia in spinal cord express low levels of the non-integrin laminin receptor precursor (LRP), also found on certain neurons and glial cells in the peripheral nervous system. 37LRP/p40 and its 67-kDa isoform laminin receptor (LR) were the first high-affinity laminin binding proteins identified. While the role of laminin receptor was later attributed to integrins, LRP/LR gained new interest as receptors for prions, and their interaction with laminin seems important for migration of metastatic cancer cells. Using immunohistochemistry and Western blotting, we demonstrate that traumatic spinal cord injury leads to a strong and rapid increase in LRP levels in relation to activated microglia/macrophages. Associated with laminin re-expression in the lesion epicenter, LRP-positive microglia/macrophages exhibit a rounded, ameboid-like shape characteristic of phagocytic cells, whereas in more distant loci they reveal a hypertrophied cell body and short ramifications. The same morphological difference is observed in vitro for purified microglia cultured with or without laminin. Strong, transient upregulation of LRP by activated spinal cord microglia is also induced by transection of the sciatic nerve that affects the spinal cord circuitry without blood-brain barrier dysruption. LRP expression is maximal by 1 week post-lesion, before becoming restricted to dorsal and ventral horns, sites of major structural reorganization. Our findings strongly suggest the involvement of LRP in lesion-induced activation and migration of microglia.

Interactions of the 67 kDa laminin receptor and its precursor with laminin

The 67LR (67 kDa laminin receptor) enables cells to interact with components of the extracellular matrix. The molecule is derived from the 37LRP (37 kDa laminin receptor precursor); however, the precise molecular mechanism of this conversion is unknown. Recombinant 37LRP, expressed in and purified from Escherichia coli, bound to human laminin in a SPR (surface plasmon resonance) experiment. 67LR isolated from human breast-cancer-derived cells in culture was also shown to bind to laminin by SPR. However, the kinetics of association are qualitatively different. 37LRP, but not 67LR, binds to heparan sulfate. The binding of 37LRP to heparan sulfate did not affect the interaction of 37LRP with laminin. In contrast, heparan sulfate reduces the extent of binding of laminin to 67LR. Taken together, these results show that 37LRP has some of the biological activities of 67LR, even prior to the conversion event. However, the conversion affects the sites of interaction with both laminin and heparan sulfate.

Multiple functions of the 37/67-kd laminin receptor make it a suitable target for novel cancer gene therapy

The 37/67-kd laminin receptor, LAMR, is a multifunctional protein that associates with the 40S ribosomal subunit and also localizes to the cell membrane to interact with the extracellular matrix. LAMR is overexpressed in many types of cancer, playing important roles in tumor-cell migration and invasion. Here, we show that LAMR is also vital for tumor-cell proliferation, survival, and protein translation. Small-interfering RNA (siRNA)-mediated reduction in expression of LAMR leads to G1 phase cell-cycle arrest in vitro by altering cyclins A2/B1, cyclin-dependent kinases (CDKs) 1/2, Survivin, and p21 expression levels. In vivo, reduction in LAMR expression results in inhibition of HT1080 cells to develop tumors. We also found that LAMR's ribosomal functions are critical for translation as reduction in LAMR expression leads to a dramatic decrease in newly synthesized proteins. Further, cells with lower expression of LAMR have fewer 40S subunits and 80S monosomes, causing an increase in free 60S ribosomal subunits. These results indicate that LAMR is able to regulate tumor development in many ways; further enhancing its potential as a target for gene therapy. To test this, we developed a novel Sindbis/Lenti pseudotype vector carrying short-hairpin RNA (shRNA) designed against lamr. This pseudotype vector effectively reduces LAMR expression and specifically targets tumors in vivo. Treatment of tumor-bearing severe combine immunodeficient (SCID) mice with this pseudotype vector significantly inhibits tumor growth. Thus, we show that LAMR can be used as a target in novel therapy for tumor reduction and elimination.

Mutational analysis of the cleavage of the cancer-associated laminin receptor by stromelysin-3 reveals the contribution of flanking sequences to site recognition and cleavage efficiency

The matrix metalloproteinase stromelysin-3 (ST3) has long been implicated to play an important role in cell fate determination during normal and pathological processes. Using the thyroid hormone-dependent Xenopus laevis metamorphosis as a model, we have previously shown that ST3 is required for apoptosis during intestinal remodeling and that laminin receptor (LR) is an in vivo substrate of ST3 during this process. ST3 cleaves LR at two distinct sites that are conserved in mammalian LR. Human ST3 and LR are both associated with tumor development and cancer progression and human LR can also be cleaved by ST3, implicating a role of LR cleavage by ST3 in human cancers. Here, we carried out a series of mutational analyses on the two cleavage sites in LR. Our findings revealed that in addition to primary sequence at the cleavage site (positions P3-P3', with the cleavage occurring between P1-P1'), flanking sequences/conformation also influenced the cleavage of LR by ST3. Furthermore, alanine substitution studies led to a surprising finding that surrounding sequence and/or conformation dictated the site of cleavage in LR by ST3. These results thus have important implications in our understanding of substrate recognition and cleavage by ST3 and argue for the importance of studying ST3 cleavage in the context of full-length substrates. Furthermore, the LR cleavage mutants generated here will also be valuable tools for future studies on the role of LR cleavage by ST3 in vertebrate development and cancer progression.

Production, safety and antitumor efficacy of recombinant Oncofetal Antigen/immature laminin receptor protein

We describe here for the first time an efficient high yield production method for clinical grade recombinant human Oncofetal Antigen/immature laminin receptor protein (OFA/iLRP). We also demonstrate significant antitumor activity for this protein when administered in liposomal delivery form in a murine model of syngeneic fibrosarcoma. OFA/iLRP is a therapeutically very promising universal tumor antigen that is expressed in all mammalian solid tumors tested so far. We have cloned the human OFA/iLRP cDNA in a bacterial expression plasmid which incorporates a 6x HIS-tag. Large scale cultures of the plasmid transformed Escherichia coli were performed and the crude HIS-tagged OFA/iLRP was isolated as inclusion bodies and solubilized in guanidine chloride. The protein was then purified by successive passage through three column chromatography steps of immobilized metal affinity, anion exchange, and gel filtration. The resulting protein was 94% pure and practically devoid of endotoxin and host cell protein. The purified OFA/iLRP was tested in mice for safety and efficacy in tumor rejection with satisfactory results. This protein will be used for loading onto autologous dendritic cells in an FDA approved phase I/II human cancer vaccine trial in OFA/iLRP-positive breast cancer patients.

Laminin receptor involvement in the anti-angiogenic activity of pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is a multifunctional protein with neurotrophic, anti-oxidative, and anti-inflammatory properties. It is also one of the most potent endogenous inhibitors of angiogenesis, playing an important role in restricting tumor growth, invasion, and metastasis. Studies show that PEDF binds to cell surface proteins, but little is known about how it exerts its effects. Recently, research identified phospholipase A(2)/nutrin/patatin-like phospholipase domain-containing 2 as one PEDF receptor. To identify other receptors, we performed yeast two-hybrid screening using PEDF as bait and discovered that the non-integrin 37/67-kDa laminin receptor (LR) is another PEDF receptor. Co-immunoprecipitation, His tag pulldown, and surface plasmon resonance assays confirmed the interaction between PEDF and LR. Using the yeast two-hybrid method, we further restricted the LR-interacting domain on PEDF to a 34-amino acid (aa) peptide (aa 44-77) and the PEDF-interacting domain on LR to a 91-aa fragment (aa 120-210). A 25-mer peptide named P46 (aa 46-70), derived from 34-mer, interacts with LR in surface plasmon resonance assays and binds to endothelial cell (EC) membranes. This peptide induces EC apoptosis and inhibits EC migration, tube-like network formation in vitro, and retinal angiogenesis ex vivo, like PEDF. Our results suggest that LR is a real PEDF receptor that mediates PEDF angiogenesis inhibition.