Regulation of no synthesis induced by inflammatory mediators in RAW264.7 cells: collagen prevents inhibition by osteopontin

Uromodulin to Osteopontin Ratio in Deceased Donor Urine Is Associated With Kidney Graft Outcomes

BACKGROUND

Deceased-donor kidneys experience extensive injury, activating adaptive and maladaptive pathways therefore impacting graft function. We evaluated urinary donor uromodulin (UMOD) and osteopontin (OPN) in recipient graft outcomes.

METHODS

Primary outcomes: all-cause graft failure (GF) and death-censored GF (dcGF). Secondary outcomes: delayed graft function (DGF) and 6-month estimated glomerular filtration rate (eGFR). We randomly divided our cohort of deceased donors and recipients into training and test datasets. We internally validated associations between donor urine UMOD and OPN at time of procurement, with our primary outcomes. The direction of association between biomarkers and GF contrasted. Subsequently, we evaluated UMOD:OPN ratio with all outcomes. To understand these mechanisms, we examined the effect of UMOD on expression of major histocompatibility complex II in mouse macrophages.

RESULTS

Doubling of UMOD increased dcGF risk (adjusted hazard ratio [aHR], 1.1; 95% confidence interval [CI], 1.02-1.2), whereas OPN decreased dcGF risk (aHR, 0.94; 95% CI, 0.88-1). UMOD:OPN ratio ≤3 strengthened the association, with reduced dcGF risk (aHR, 0.57; 0.41-0.80) with similar associations for GF, and in the test dataset. A ratio ≤3 was also associated with lower DGF (aOR, 0.73; 95% CI, 0.60-0.89) and higher 6-month eGFR (adjusted β coefficient, 3.19; 95% CI, 1.28-5.11). UMOD increased major histocompatibility complex II expression elucidating a possible mechanism behind UMOD's association with GF.

CONCLUSIONS

UMOD:OPN ratio ≤3 was protective, with lower risk of DGF, higher 6-month eGFR, and improved graft survival. This ratio may supplement existing strategies for evaluating kidney quality and allocation decisions regarding deceased-donor kidney transplantation.

Osteopontin in macrophage function

The secreted phosphorylated protein osteopontin (OPN) is expressed in a variety of tissues and bodily fluids, and is associated with pathologies including tissue injury, infection, autoimmune disease and cancer. Macrophages are ubiquitous, heterogeneous cells that mediate aspects of cell and tissue damage in all these pathologies. Here, the role of OPN in macrophage function is reviewed. OPN is expressed in macrophage cells in multiple pathologies, and the regulation of its expression in these cells has been described in vitro. The protein has been implicated in multiple functions of macrophages, including cytokine expression, expression of inducible nitric oxide synthase, phagocytosis and migration. Indeed, the role of OPN in cells of the macrophage lineage might underlie its physiological role in many pathologies. However, there are numerous instances where the published literature is inconsistent, especially in terms of OPN function in vitro. Although the heterogeneity of OPN and its receptors, or of macrophages themselves, might underlie some of these inconsistencies, it is important to understand the role of OPN in macrophage biology in order to exploit its function therapeutically.

Clinical significance of osteopontin expression in T1 and T2 tongue cancers

BACKGROUND

Osteopontin (OPN) is considered to be a tumor-related protein associated with tumor aggressiveness and metastasis.

METHODS

Immunohistochemistry was used to study the clinical significance of OPN expression in T1 and T2 tongue cancers.

RESULTS

Positive OPN expression significantly correlated with higher tumor classification (T) (p = .004), positive nodal classification (N) (p < .001), greater tumor thickness (p < .001), and presence of tumor necrosis (p = .016), respectively. The unfavorable cumulative 5-year disease-free survival rate significantly correlated with positive OPN expression (p < .001), T2 (p = .024), positive N (p < .001), greater tumor thickness (p = .023), and positive tumor necrosis (p = .003). However, taking CD105 into consideration, only CD105 expression was the independent prognostic factor for survival by Cox's regression analysis.

CONCLUSION

Overexpression of OPN in the tumors implicated a more aggressive tumor behavior and was an important factor for survival. In addition, there might be relationship between OPN and CD105 expressions in angiogenesis.

Genetic networks of cooperative redox regulation of osteopontin

Osteopontin is a primary cytokine and matrix-associated protein involved in medial thickening and neointima formation. Osteopontin binds integrin receptors, activates cell migration and matrix metalloproteinases, and mediates arteriosclerotic lesion formation and vessel calcification. To understand the complex biology of osteopontin, computational methodology was employed to identify sets of genes whose transcriptional states were predictive of osteopontin gene expression based on the transcriptional states of 12,400 genes and ESTs across 235 independent Affymetrix Murine Genome Array MG_U74Av2 hybridizations. Arginase [GenBank: U51805] and Mac-2 antigen [GenBank: X16834] were identified as primary attractors within the gene-gene interaction network of osteopontin. Resolution of molecular interactions among these genes indicated that the majority of predictor genes could be linked through redox regulated transcription by nuclear factor kappa-B and transforming growth factor beta inducible early gene 1 regulatory elements. Subsequent molecular analyses established redox sensitivity of a 200 bp region within the 5' UTR of opn promoter and implicated nuclear factor kappa-B and transforming growth factor beta inducible early gene 1 cis-acting elements in the regulation of osteopontin.

Elevation of plasma osteopontin level in patients with undifferentiated nasopharyngeal carcinoma

AIMS

We evaluated the clinicopathologic relevance of plasma osteopontin (OPN) level in nasopharyngeal carcinoma patients.

METHODS

Seventy-two plasma samples were collected from patients with undifferentiated nasopharyngeal carcinoma (NPC) before radiotherapy. Plasma OPN level was determined by quantitative sandwich enzyme immunoassay. The plasma OPN level was evaluated for its clinicopathologic relevance.

RESULTS

The mean plasma OPN level was significantly higher in NPC patients than in normal controls (184.66 vs 75.89 ng/ml, p<0.001). In addition, high OPN level was found in the patients with advanced cancer and was correlated with neck node metastasis (p<0.05).

CONCLUSIONS

Our findings indicated a potential role of OPN in the pathogenesis and nodal metastasis of undifferentiated NPC.

Transcriptional Regulatory Functions of Heterogeneous Nuclear Ribonucleoprotein-U and -A/B in Endotoxin-Mediated Macrophage Expression of Osteopontin

Osteopontin (OPN) is a highly hydrophilic and negatively charged sialoprotein of approximately 298 amino acids with diverse regulatory functions, including cell adhesion and migration, tumor growth and metastasis, atherosclerosis, aortic valve calcification, and repair of myocardial injury. OPN is unique as an endogenous negative feedback inhibitor of NO expression. However, the specific cis- and trans-regulatory elements that determine the extent of endotoxin (LPS)- and NO-mediated induction of OPN synthesis are unknown. We have previously shown that LPS-induced S-nitrosylation of heterogeneous nuclear ribonucleoprotein (hnRNP)-A/B inhibits its activity as a constitutive trans-repressor of the OPN transcription by significantly decreasing its DNA binding activity. hnRNPs were originally described as chromatin-associated RNA-binding proteins that form complexes with RNA polymerase II transcripts. The hnRNP family is comprised of >20 proteins that contribute to the complex around nascent pre-mRNA and are thus able to modulate RNA processing. In this subsequent study, again using RAW 264.7 murine macrophages and COS-1 cells, we demonstrate that hnRNP-A/B and hnRNP-U proteins serve antagonistic transcriptional regulatory functions for OPN expression in the setting of LPS-stimulated NO synthesis. In the presence of NO, hnRNP-A/B dissociates from its OPN promoter site with subsequent derepression of OPN promoter activity. Subsequently, hnRNP-U binds to the same site to further augment OPN promoter activation. This has not been previously described for the hnRNP proteins. Our results represent a unique transcriptional regulatory mechanism which involves interplay between members of the hnRNP protein family.

Effect of osteopontin alleles on beta-glucan-induced granuloma formation in the mouse liver

The granuloma formation is a host defense response against persistent irritants. Osteopontin is centrally involved in the formation of granulomas. Three osteopontin alleles, designated a, b, and c, have been found in mice. Here we used a murine model of zymosan (beta-glucan)-induced granuloma formation in the liver to determine possible functional differences between the osteopontin alleles in cell-mediated immunity. In contrast to mice with alleles a or c, mice with the allele b was defective in granuloma formation. As detected by mRNA expression, cytokines and chemokines known to be critically involved in granuloma formation were elicited in liver tissue, regardless of the osteopontin allele expressed. Alignment of the deduced amino acid sequences showed that unlike osteopontin c, b differs from a in 11 amino acids. All three osteopontin alleles had normal cell-binding properties. However, only the b allelic form was defective in the induction of cell migration as tested with dendritic cells. In conclusion, generation of a granulomatous response in mice depends critically on the presence of a functional osteopontin allele. Defective granuloma formation in mice with allele b is likely to be because of an impaired chemotactic function of the osteopontin b protein on immunocompetent cells.

Impaired anti-tumor cytotoxicity of macrophages from osteopontin-deficient mice

Osteopontin (OPN) expression in tumors is associated with more aggressive tumor growth; however, several studies have suggested that OPN as a host protein can regulate tumor growth as well. OPN is produced by macrophages and T cells, and reportedly modifies macrophage function. Here, we have investigated the effect of OPN on macrophage function, and its role in host defense against tumor growth. OPN deficient (-/-) and wild-type (WT) peritoneal macrophages were assessed for their ability to mediate cytotoxicity of tumor cells. Thioglycollate-elicited peritoneal exudate cells (PEC) were stimulated in vitro with interferon-gamma and lipopolysaccharide. [(3)H]Thymidine-labeled ras-transformed tumor cells were then added and (3)H release and nitrite accumulation were measured. OPN -/- PEC exhibited as much as a 70% reduction in cytotoxicity as compared to WT PEC. Tumor cell OPN status, on the other hand, had little effect on the extent of cytotoxicity. Production of nitrite by the PEC correlated with their capacity to kill tumor cells. L-929 cells, which are relatively resistant to nitric oxide-induced cytotoxicity and sensitive to that effected by TNF-alpha, were killed equally well by wild-type and OPN-deficient PEC, suggesting that the effect of OPN is not mediated through TNF-alpha. No difference was seen in the cytotoxicity of resident macrophages from mice of different genotypes, indicating that the defect in the OPN-deficient macrophages may result from altered differentiation in vivo. In support of this idea, we show that the expression of the macrophage markers F4/80 in peritoneal cells and of Mac-2 in spleen cells is altered in OPN -/- mice as compared to WT. These data support the hypothesis that host-derived osteopontin may inhibit tumor growth and provide a mechanism for this effect.

Role of osteopontin in murine Lyme arthritis and host defense against Borrelia burgdorferi

Several genetic loci in the mouse have been identified that regulate the severity of Lyme arthritis. The region of chromosome 5 including the osteopontin (OPN) gene (Opn) has been identified in intercross populations of C3H/HeN x C57BL/6 and C3H/HeJ x BALB/cAnN mice. OPN is of particular interest as it is involved in the maintenance and remodeling of tissue during inflammation, it regulates production of interleukin-10 (IL-10) and IL-12 (cytokines implicated in Lyme arthritis), it is necessary for host control of certain bacterial infections, and mice displaying different severities of Lyme arthritis possess different alleles of the OPN gene. Macrophages and splenocytes from OPN-deficient mice on mixed C57BL/6J-129S or inbred 129S backgrounds were stimulated with the Pam(3)Cys modified lipoprotein from Borrelia burgdorferi, OspA. OPN was not required for OspA-induced cytokine production; however, macrophages from 129S-Opn(-/-) mice displayed a reduced level of IL-10 production. OPN was also not required for resistance to severe arthritis, as B. burgdorferi-infected 129S-Opn(-/-) mice developed mild arthritis, as did their wild-type littermates. Arthritis was more severe in OPN-deficient mice on the mixed C57BL/6J-129S backgrounds than in inbred mice of either strain. This increase was most likely due to a gene(s) closely linked to Opn on chromosome 5 in conjunction with other randomly assorting genes. Deficiency in OPN did not influence the numbers of spirochetes in tissues from B. burgdorferi-infected mice, indicating OPN is not part of the host defense to this pathogen. Interestingly, there was no alteration in the B. burgdorferi-specific antibody isotypes in OPN-deficient mice, indicating that its effect on helper T-cell responses is not relevant to the host response to B. burgdorferi.

Role of osteopontin in cellular signaling and toxicant injury

Osteopontin (OPN) is a glycosylated phosphoprotein found in all body fluids and in the proteinaceous matrix of mineralized tissues. It can function both as a cell attachment protein and as a cytokine, delivering signals to cells via a number of receptors including several integrins and CD44. Expression of OPN is enhanced by a variety of toxicants, especially those that activate protein kinase C. In its capacity as a signaling molecule, OPN can modify gene expression and promote the migration of monocytes/macrophages up an OPN gradient. It has both inflammatory and anti-inflammatory actions. Some experiments suggest that it may inhibit apoptosis, possibly contributing to the survival of cells in response to toxicant injury. Elevated OPN expression often correlates with malignancy and has been shown to enhance the tumorigenic and/or metastatic phenotype of the cancer cell. Recent studies have revealed that OPN plays critical roles in bone remodeling and cell-mediated immunity.