Experimental and clinical evidence suggests that tumor-associated macrophages (TAMs) play important roles in cancer progression. Here, we have characterized the ontogeny and function of TAM subsets ...in a mouse model of metastatic ovarian cancer that is representative for visceral peritoneal metastasis. We show that the omentum is a critical premetastatic niche for development of invasive disease in this model and define a unique subset of CD163+ Tim4+ resident omental macrophages responsible for metastatic spread of ovarian cancer cells. Transcriptomic analysis showed that resident CD163+ Tim4+ omental macrophages were phenotypically distinct and maintained their resident identity during tumor growth. Selective depletion of CD163+ Tim4+ macrophages in omentum using genetic and pharmacological tools prevented tumor progression and metastatic spread of disease. These studies describe a specific role for tissue-resident macrophages in the invasive progression of metastatic ovarian cancer. The molecular pathways of cross-talk between tissue-resident macrophages and disseminated cancer cells may represent new targets to prevent metastasis and disease recurrence.
Haptoglobin, the haptoglobin-hemoglobin receptor CD163, and the heme oxygenase-1 are proteins with a well-established function in the clearance and metabolism of “free” hemoglobin released during ...intravascular hemolysis. This scavenging system counteracts the potentially harmful oxidative and NO-scavenging effects associated with “free” hemoglobin, and, furthermore, elicits an anti-inflammatory response. In the late primate evolution, haptoglobin variants with distinct functions have arisen, including haptoglobin polymers and the haptoglobin-related protein. The latter associates with a subspecies of high-density lipoprotein (HDL) particles playing a crucial role in the innate immunity against certain trypanosome parasites. Recent studies have elucidated this fairly sophisticated immune defense mechanism that takes advantage of a trypanosomal haptoglobin-hemoglobin receptor evolved to supply the parasite with heme. Because of the high resemblance between haptoglobin and haptoglobin-related protein, the receptor also takes up the complex of hemoglobin and the HDL-bound haptoglobin-related protein. This tricks the parasite into internalizing another HDL-associated protein and toxin, apolipoprotein L-I, that kills the parasite. In conclusion, variant human homologous hemoglobin-binding proteins that collectively may be designated the haptoglobins have diverted from the haptoglobin gene. On hemoglobin and receptor interaction, these haptoglobins contribute to different biologic events that go beyond simple removal from plasma of the toxic hemoglobin.
Structure of the haptoglobin―haemoglobin complex FOISTED ANDERSEN, Christian Brix; TORVUND-JENSEN, Morten; PINTO JENSBY NIELSEN, Marianne ...
Nature (London),
09/2012, Letnik:
489, Številka:
7416
Journal Article
Recenzirano
Red cell haemoglobin is the fundamental oxygen-transporting molecule in blood, but also a potentially tissue-damaging compound owing to its highly reactive haem groups. During intravascular ...haemolysis, such as in malaria and haemoglobinopathies, haemoglobin is released into the plasma, where it is captured by the protective acute-phase protein haptoglobin. This leads to formation of the haptoglobin-haemoglobin complex, which represents a virtually irreversible non-covalent protein-protein interaction. Here we present the crystal structure of the dimeric porcine haptoglobin-haemoglobin complex determined at 2.9 Å resolution. This structure reveals that haptoglobin molecules dimerize through an unexpected β-strand swap between two complement control protein (CCP) domains, defining a new fusion CCP domain structure. The haptoglobin serine protease domain forms extensive interactions with both the α- and β-subunits of haemoglobin, explaining the tight binding between haptoglobin and haemoglobin. The haemoglobin-interacting region in the αβ dimer is highly overlapping with the interface between the two αβ dimers that constitute the native haemoglobin tetramer. Several haemoglobin residues prone to oxidative modification after exposure to haem-induced reactive oxygen species are buried in the haptoglobin-haemoglobin interface, thus showing a direct protective role of haptoglobin. The haptoglobin loop previously shown to be essential for binding of haptoglobin-haemoglobin to the macrophage scavenger receptor CD163 (ref. 3) protrudes from the surface of the distal end of the complex, adjacent to the associated haemoglobin α-subunit. Small-angle X-ray scattering measurements of human haptoglobin-haemoglobin bound to the ligand-binding fragment of CD163 confirm receptor binding in this area, and show that the rigid dimeric complex can bind two receptors. Such receptor cross-linkage may facilitate scavenging and explain the increased functional affinity of multimeric haptoglobin-haemoglobin for CD163 (ref. 4).
The hemoglobin scavenger receptor CD163 is exclusively expressed in the monocytic lineage and preferentially in tissue resident macrophages of the M2 phenotype and in macrophages in sites of ...inflammation and tumor growth. In the present study we have designed liposomes specifically targeting CD163 by hydrophobic linkage of CD163-binding monoclonal antibodies to polyethylene glycol-coated liposomes (‘stealth liposomes’). Targeting to the endocytic CD163 protein greatly increased the uptake of liposomes in CD163 transfected cells and macrophages as visualized by confocal microscopy and flow cytometry of cells exposed to CD163 targeting liposomes loaded with calcein. Strong cytotoxic effects were seen in CD163-expressing human monocytes by using the chemotherapeutic agent doxorubicin as cargo of the liposomes.
In conclusion, the use of stealth liposomes modified to recognize CD163 is a potential way to target drugs to macrophages that support inflammatory and malignant processes.
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CD163 is expressed specifically in the monocyte/macrophage lineage, where it mediates uptake of haptoglobin-hemoglobin complexes, leading to metabolism of the oxidative heme molecule. Shedding of the ...CD163 ectodomain from the cell surface produces a sCD163 plasma protein, and a positive correlation is seen between the sCD163 plasma level and the severity of various infectious and inflammatory diseases. In the present analysis of the phorbol ester-induced shedding of sCD163 in CD163 cDNA-transfected HEK293 cells, we used metalloproteinase inhibitors and siRNA-mediated inhibition of metalloproteinases to identify TACE/ADAM17 as an enzyme responsible for PMA-induced cleavage of the membrane-proximal region of CD163. As TACE/ADAM17-mediated shedding of TNF-α is up-regulated in macrophages subjected to inflammatory stimuli, the present results now provide a likely explanation for the strong empirical relationship between the sCD163 plasma level and infectious/inflammatory diseases relating to macrophage activity.
The hemoglobin receptor CD163 and the mannose receptor CD206 are both expressed on the surface of human macrophages. Upon inflammatory activation, the receptors are shed from the macrophage surface ...generating soluble products. The plasma concentration of both soluble CD163 (sCD163) and soluble CD206 (sCD206) are increased in several diseases, including inflammatory conditions and cancer. Here, we show that in contrast to CD163, LPS-mediated shedding of CD206 in humans is slow and a result of indirect signaling. Although both sCD163 and sCD206 were increased in response to LPS stimulation in vivo, only CD163 was shed from LPS-stimulated macrophages in vitro. Although both sCD163 and sCD206 were released from cultured macrophages stimulated with zymosan and PMA, shedding of CD206 was generally slower and less efficient and not reduced by inhibitors against the major protease classes. These data indicate that CD163 and CD206 are shed from the macrophages by very different mechanisms potentially involving distinctive inflammatory processes.
The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved ...protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.
The endocytic receptor cubam formed by the 460-kDa protein cubilin and the 45-kDa transmembrane protein amnionless (AMN), is essential for intestinal vitamin B
(B
) uptake and for protein (e.g. ...albumin) reabsorption from the kidney filtrate. Loss of function of any of the two components ultimately leads to serious B
deficiency and urinary protein loss in humans (Imerslund-Gräsbeck's syndrome, IGS). Here, we present the crystal structure of AMN in complex with the amino-terminal region of cubilin, revealing a sophisticated assembly of three cubilin subunits combining into a single intertwined β-helix domain that docks to a corresponding three-faced β-helix domain in AMN. This β-helix-β-helix association thereby anchors three ligand-binding cubilin subunits to the transmembrane AMN. Electron microscopy of full-length cubam reveals a 700-800 Å long tree-like structure with the potential of dimerization into an even larger complex. Furthermore, effects of known human mutations causing IGS are explained by the structural information.
Heme, the functional group of hemoglobin, myoglobin, and other hemoproteins, is a highly toxic substance when it appears in the extracellular milieu. To circumvent potential harmful effects of heme ...from hemoproteins released during physiological or pathological cell damage (such as hemolysis and rhabdomyolysis), specific high capacity scavenging systems have evolved in the mammalian organism. Two major systems, which essentially function in a similar way by means of a circulating latent plasma carrier protein that upon ligand binding is recognized by a receptor, are represented by a) the hemoglobin-binding haptoglobin and the receptor CD163, and b) the heme-binding hemopexin and the receptor low density lipoprotein receptor-related protein/CD91. Apart from the disclosure of the molecular basis for these important heme scavenging systems by identifying the functional link between the carrier proteins and the respective receptors, research over the last decade has shown how these systems, and the metabolic pathways they represent, closely relate to inflammation and other biological events.
Tumor‐associated macrophages (TAMs) represent a distinct malignancy‐promoting phenotype suggested to play a key role in tumor formation and metastasis. We aimed to investigate the expression of the ...monocyte/macrophage‐restricted receptor CD163 in bladder tumor biopsies and assess the potential mechanism inducing the CD163 expression in tumor cells. A high CD163 mRNA expression (n = 87) was significantly associated with a poor 13‐year overall survival (log‐rank test, χ2 = 8.931; p = 0.0028). Moreover, CD163 mRNA expression was significantly increased in muscle invasive (T2–T4), p = 0.017, and aggressive (grade III/IV) cancers (p = 0.015). The expression strongly correlated with local expression of IL‐6 (r = 0.72; p <0.0001) and IL‐10 (r = 0.75; p <0.0001), mediators known to induce CD163 expression in vitro. CD163 immunostaining (n = 46) confirmed the association between dense TAM infiltration and histologically advanced disease. In 39% of the biopsies, CD163 immunoreactivity was also observed in tumor cells, and CD163‐expressing metastatic cells were identified in lymph node biopsies (n = 8). Bladder cancer cell lines did not express CD163; however, when cocultured with macrophages the bladder cancer cell expression of CD163 was significantly induced in an IL‐6/IL‐10 independent manner. In conclusion, we show a strong association between CD163 mRNA expression in bladder cancer biopsies and poor patient outcome. CD163 expression was not confined to the infiltrating TAMs, but was also expressed by a significant portion of the malignant cells in both tumors and lymph nodes. CD163 expressing tumor cells may constitute a subpopulation of tumor cells with a phenotypic shift associated with epithelial‐to‐mesenchymal transition (EMT) and increased metastatic activity induced by TAMs.
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