Low density lipoprotein receptor-related protein (LRP) expression varies among Hep G2 cell lines

Differences in Genetic Background Contribute to Pseudomonas Exotoxin A-Induced Hepatotoxicity in Rats

Pseudomonas aeruginosa exotoxin A (PEA) causes severe hepatotoxicity in experimental animals and is useful in investigations of immune-mediated liver injury. However, strain differences in the sensitivity to PEA-induced hepatotoxicity in rats remains be elucidated. In this study, we determined the severity of PEA-induced hepatotoxicity in six genetically different rat strains. Male LE (Long Evans), Wistar, F344, WKY, BN/SsN and LEW rats were administered a single intravenous injection of PEA (20 μg/kg). Significantly elevated serum ALT and AST levels, massive necrosis and hemorrhage, and numerous TUNEL-positive hepatocytes were observed in BN/SsN rats. In contrast, low levels of ALT and AST as well as mild changes in liver histopathology were observed in Wistar and F344 rats. Moderate levels of hepatic injuries were observed in LE, WKY, and LEW rats. Pro-inflammatory cytokines including TNF-α, IL-2 and IL-6 serum levels were markedly increased in BN/SsN rats compared to Wistar and F344 rats. However, the hepatic levels of low density lipoprotein receptor-related protein (LRP), which functions as the PEA receptor, were not significantly different in each strain. Taken together, we suggest that BN/SsN is the most sensitive rat strain, whereas Wistar and F344 were the most resistant rat strains to PEA-induced liver damage. The different genetic background of rat strains plays an important role in the susceptibility to PEA-induced epatotoxicity that may depend on immune-regulation but not LRP receptor levels.

Specific deletion of LDL receptor-related protein on macrophages has skewed in vivo effects on cytokine production by invariant natural killer T cells

Expression of molecules involved in lipid homeostasis such as the low density lipoprotein receptor (LDLr) on antigen presenting cells (APCs) has been shown to enhance invariant natural killer T (iNKT) cell function. However, the contribution to iNKT cell activation by other lipoprotein receptors with shared structural and ligand binding properties to the LDLr has not been described. In this study, we investigated whether a structurally related receptor to the LDLr, known as LDL receptor-related protein (LRP), plays a role in iNKT cell activation. We found that, unlike the LDLr which is highly expressed on all immune cells, the LRP was preferentially expressed at high levels on F4/80+ macrophages (MΦ). We also show that CD169+ MΦs, known to present antigen to iNKT cells, exhibited increased expression of LRP compared to CD169- MΦs. To test the contribution of MΦ LRP to iNKT cell activation we used a mouse model of MΦ LRP conditional knockout (LRP-cKO). LRP-cKO MΦs pulsed with glycolipid alpha-galactosylceramide (αGC) elicited normal IL-2 secretion by iNKT hybridoma and in vivo challenge of LRP-cKO mice led to normal IFN-γ, but blunted IL-4 response in both serum and intracellular expression by iNKT cells. Flow cytometric analyses show similar levels of MHC class-I like molecule CD1d on LRP-cKO MΦs and normal glycolipid uptake. Survey of the iNKT cell compartment in LRP-cKO mice revealed intact numbers and percentages and no homeostatic disruption as evidenced by the absence of programmed death-1 and Ly-49 surface receptors. Mixed bone marrow chimeras showed that the inability iNKT cells to make IL-4 is cell extrinsic and can be rescued in the presence of wild type APCs. Collectively, these data demonstrate that, although MΦ LRP may not be necessary for IFN-γ responses, it can contribute to iNKT cell activation by enhancing early IL-4 secretion.

Regulation of LRP-1 expression: make the point

The low-density lipoprotein receptor-related protein-1 (LRP-1) is a membrane receptor displaying both scavenging and signaling functions. The wide variety of extracellular ligands and of cytoplasmic scaffolding and signaling proteins interacting with LRP-1 gives it a major role not only in physiological processes, such as embryogenesis and development, but also in critical pathological situations, including cancer and neurological disorders. In this review, we describe the molecular mechanisms involved at distinct levels in the regulation of LRP-1, from its expression to the proper location and stability at the cell surface.

Soluble low-density lipoprotein receptor-related protein

Soluble forms of receptors can influence the activity of their membrane-bound counterparts by affecting their interactions with ligands. Low density lipoprotein (LDL) receptor-related protein (LRP), a member of the LDL receptor family, binds multiple classes of ligands and has been implicated in a broad range of normal and disease processes involving lipid metabolism, protease clearance, and cell migration. We recently identified a soluble form of LRP (sLRP) in human plasma and showed that it retains LRP-ligand binding ability. These findings open potentially important additional aspects in the biology of this multifunctional receptor. This review summarizes characteristics of soluble LRP and relates these to the membrane-bound form of the receptor.

C766T low-density lipoprotein receptor-related protein 1 (LRP1) gene polymorphism and susceptibility to breast cancer

BACKGROUND

Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional endocytic receptor with an important role in regulating the activity of proteinases in extracellular matrix. Several studies have also described its role in intracellular signaling. Previous studies showed that the expression of LRP1 is related to invasiveness of cancer cells. However, recent data on LRP1 suggest that this receptor can also be involved in tumor establishment and progression.

METHODS

We investigated an association between the C766T polymorphism of the third exon of the LRP1 gene and breast cancer in a sample of women of Caucasian origin. Allele and genotype frequencies of this polymorphism were assessed in 164 women with breast cancer and in 183 age-compatible women without a history of any cancer disease.

RESULTS

An increase in LRP1 T allele frequency in subjects with breast cancer was observed compared with controls (0.21 versus 0.15, P = 0.01963). A significant excess of genotypes with the T allele (homozygotes plus heterozygotes) was also observed (odds ratio 1.743, 95% confidence interval 1.112-2.732).

CONCLUSION

The T allele of the C766T polymorphism in the LRP1 gene is associated with an increased risk of breast cancer development in women of Caucasian origin.

Control of apolipoprotein E secretion in the human hepatoma cell line KYN-2

Even though it is known that apolipoprotein E (apoE) is deeply involved in major age-related disorders such as atherosclerosis or Alzheimer's disease (AD), the control of cell-specific apoE expression is still poorly understood. We compared the apoE secretion as previously described in astrocytic cell17 to hepatic cell apoE secretion. We used the human hepatoma cell line KYN-2 to better delineate the characteristics of apoE secretion and to validate it with respect to the classical human hepatoma cell line HepG2. Interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) significantly inhibited, while IL-2, IL-6 and tumour necrosis factor-alpha (TNF-alpha) were inactive on apoE secretion by KYN-2 as well as HepG2 cells. Cholesterol and 25-OH cholesterol had no effect, while forskolin exerted a significant inhibitory effect, on apoE secretion in KYN-2 cells. Our results suggest that the KYN-2 cell line represents an appropriate cell model, and in any case an alternative model to the HepG2 cell line, to study the control of apoE secretion. The response of KYN-2 cells to both cytokines and cholesterol differs from that found in astrocytoma cells, suggesting that blood variations of apoE concentrations in AD may not reflect the dysregulations taking place in the brain.

Evolutionary conservation of circulating soluble low density lipoprotein receptor-related protein-like ("LRP-like") molecules

Low density lipoprotein receptor family members characteristically bind 39-kDa receptor associated protein (RAP). Soluble forms of these receptors have been described in humans including the 515/85-kDa dimeric receptor, low density lipoprotein receptor-related protein (LRP/alpha2MR), which is involved in multiple processes including lipoprotein and protease metabolism. Here we demonstrate evolutionary conservation in the generation of these soluble RAP-binding proteins of high molecular weight, by identifying their presence in mammalian, avian, and reptilian sera as well as in the circulating haemolymph of a mollusc. Sera extracted on immobilized RAP, produced bands at approximately 500 kDa in radiolabeled ligand blots by using the LRP/alpha2MR-specific ligand, Pseudomonas exotoxin A (PEA). These findings suggest that circulating RAP-binding proteins with high molecular weight in vertebrates share features of LRP/alpha2MR (LRP-like molecules). RAP-binding molecules in the mammalian serum extracts were further characterized as LRP/alpha2MR homologues in Western blots by using antibodies against the 515-kDa alpha-chain of LRP/alpha2MR. Western blots of mammalian serum extracts using two monoclonal antibodies recognizing the 85-kDa transmembrane beta-chain suggested that a portion of the beta-chain's ectodomain remains associated with the alpha-chain, but the beta-chain's intracellular carboxy terminus is absent. These results are consistent with evolutionary conservation in the generation, composition, and ligand-binding ability of soluble LRP-like receptors and suggest that their presence is a necessary aspect of the receptor's function.

Low density lipoprotein receptor related protein gene amplification and 766T polymorphism in astrocytomas

Low density lipoprotein receptor related protein (LRP) is a receptor for protease complexes, and may function in cell growth and repair, and in tumor invasiveness. LRP expression increases in glioblastomas compared to lower grade astrocytomas. Two potential mechanisms for this increased expression were investigated. The LRP C766T polymorphism is protective against Alzheimer's disease, perhaps through alteration of LRP expression. The frequency of the polymorphism was measured in astrocytoma patients and controls, but no significant difference was found. Differential PCR revealed LRP gene amplification in four of 25 high-grade gliomas and 0 of 23 other brain tumors. Co-amplification with epidermal growth factor receptor (EGFR) occurred in all four of the LRP-amplified tumors. Thus, LRP amplification may be partly responsible for increased LRP expression in astrocytomas, and may often occur in conjunction with EGFR amplification.