Role of C5b-9 complement complex and response gene to complement-32 (RGC-32) in cancer

Is the Complement System Dysregulated in Preeclampsia Comorbid with HIV Infection?

South Africa is the epicentre of the global HIV pandemic, with 13.9% of its population infected. Preeclampsia (PE), a hypertensive disorder of pregnancy, is often comorbid with HIV infection, leading to multi-organ dysfunction and convulsions. The exact pathophysiology of preeclampsia is triggered by an altered maternal immune response or defective development of maternal tolerance to the semi-allogenic foetus via the complement system. The complement system plays a vital role in the innate immune system, generating inflammation, mediating the clearance of microbes and injured tissue materials, and a mediator of adaptive immunity. Moreover, the complement system has a dual effect, of protecting the host against HIV infection and enhancing HIV infectivity. An upregulation of regulatory proteins has been implicated as an adaptive phenomenon in response to elevated complement-mediated cell lysis in HIV infection, further aggravated by preeclamptic complement activation. In light of the high prevalence of HIV infection and preeclampsia in South Africa, this review discusses the association of complement proteins and their role in the synergy of HIV infection and preeclampsia in South Africa. It aims to identify women at elevated risk, leading to early diagnosis and better management with targeted drug therapy, thereby improving the understanding of immunological dysregulation.

C5b-9 promotes ferritinophagy leading to ferroptosis in renal tubular epithelial cells of trichloroethylene-sensitized mice

Trichloroethylene (TCE) is a common environmental contaminant that can cause a severe allergic reaction called TCE hypersensitivity syndrome, which often implicates the patient's kidneys. Our previous study revealed that C5b-9-induced tubular ferroptosis is involved in TCE-caused kidney damage. However, the study did not explain how tubule-specific C5b-9 causes free iron overload, a key event in ferroptosis. Here, we aimed to explore the role of NCOA4-mediated ferritinophagy in C5b-9-induced iron overload and ferroptosis in TCE-sensitized mice. Our results showed that TCE sensitization does not affect iron import or export, but does affect iron storage, causing ferritin degradation and free iron overload. In addition, mitochondrial ROS was upregulated, and these changes were blocked by C5b-9 inhibition. Interestingly, TCE-induced ferritin degradation and ferroptosis were significantly antagonized by the application of the mitochondrial ROS inhibitor, Mito-TEMPO. Moreover, all of these modes of action were further verified in C5b-9-attack signalling HK-2 cells. Further investigation demonstrated that C5b-9-upregulated mitochondrial ROS induced a marked increase in nuclear receptor coactivator 4 (NCOA4), a master regulator of ferritinophagy. In addition, the application of NCOA4 small interfering RNA not only significantly reversed ferritinophagy caused by C5b-9 but also reduced C5b-9-induced ferroptosis in HK-2 cells. Taken together, these results suggest that tubule-specific C5b-9 deposition activates NCOA4 through the upregulation of mitochondrial ROS, causing ferritin degradation and elevated free iron, which ultimately leads to tubular epithelial cell ferroptosis and kidney injury in TCE-sensitized mice.

The role of Map1b in regulating osteoblast polarity, proliferation, differentiation and migration

Osteoblast polarity, proliferation, differentiation, and migration are essential for maintaining normal bone structure and function. While the microtubule-associated protein Map1b has been extensively studied in nerve cells, its role in bone cells is less known. We investigated the functional significance of Map1b in mouse bone marrow stromal cells (ST2) and elucidated its relationship and influence on cytoskeletal polarity and Golgi organization. Our results suggest that Map1b, as a microtubule regulatory protein, can also regulate the expression of cyclin PCNA, p-H3(S10) and migration-related protein integrin β1, thereby affecting the proliferation and migration of osteoblasts. The downstream target gene Rgc32 was screened by RNA sequencing. Furthermore, Map1b, as a downstream mediator, regulates the Wnt5a signaling pathway. This study expands our understanding of the involvement of Map1b in bone biology and highlights its crucial role in governing osteoblast polarity, proliferation, and migration, thereby providing a basis for developing novel therapeutic strategies targeting Map1b in orthopedic medicine and promoting precision treatment modalities. Further investigations on the precise mechanisms underlying Map1b's influence on bone cell function and disease progression are needed.

The Role of the Complement in Clear Cell Renal Carcinoma (ccRCC)-What Future Prospects Are There for Its Use in Clinical Practice?

In recent years, the first-line available therapeutic options for metastatic renal cell carcinoma (mRCC) have radically changed with the introduction into clinical practice of new immune checkpoint inhibitor (ICI)-based combinations. Many efforts are focusing on identifying novel prognostic and predictive markers in this setting. The complement system (CS) plays a central role in promoting the growth and progression of mRCC. In particular, mRCC has been defined as an "aggressive complement tumor", which encompasses a group of malignancies with poor prognosie and highly expressed complement components. Several preclinical and retrospective studies have demonstrated the negative prognostic role of the complement in mRCC; however, there is little evidence on its possible role as a predictor of the response to ICIs. The purpose of this review is to explore more deeply the physio-pathological role of the complement in the development of RCC and its possible future use in clinical practice as a prognostic and predictive factor.

RGCC-mediated PLK1 activity drives breast cancer lung metastasis by phosphorylating AMPKα2 to activate oxidative phosphorylation and fatty acid oxidation

BACKGROUND

More than 90% of the mortality of triple-negative breast cancer (TNBC) patients is attributed to cancer metastasis with organotropism. The lung is a frequent site of TNBC metastasis. However, the precise molecular mechanism for lung-specific metastasis of TNBC is not well understood.

METHODS

RNA sequencing was performed to identify patterns of gene expression associated with lung metastatic behavior using 4T1-LM3, MBA-MB-231-LM3, and their parental cells (4T1-P, MBA-MB-231-P). Expressions of RGCC, called regulator of cell cycle or response gene to complement 32 protein, were detected in TNBC cells and tissues by qRT-PCR, western blotting, and immunohistochemistry. Kinase activity assay was performed to evaluate PLK1 kinase activity. The amount of phosphorylated AMP-activated protein kinase α2 (AMPKα2) was detected by immunoblotting. RGCC-mediated metabolism was determined by UHPLC system. Oxidative phosphorylation was evaluated by JC-1 staining and oxygen consumption rate (OCR) assay. Fatty acid oxidation assay was conducted to measure the status of RGCC-mediated fatty acid oxidation. NADPH and ROS levels were detected by well-established assays. The chemical sensitivity of cells was evaluated by CCK8 assay.

RESULTS

RGCC is aberrantly upregulated in pulmonary metastatic cells. High level of RGCC is significantly related with lung metastasis in comparison with other organ metastases. RGCC can effectively promote kinase activity of PLK1, and the activated PLK1 phosphorylates AMPKα2 to facilitate TNBC lung metastasis. Mechanistically, the RGCC/PLK1/AMPKα2 signal axis increases oxidative phosphorylation of mitochondria to generate more energy, and promotes fatty acid oxidation to produce abundant NADPH. These metabolic changes contribute to sustaining redox homeostasis and preventing excessive accumulation of potentially detrimental ROS in metastatic tumor cells, thereby supporting TNBC cell survival and colonization during metastases. Importantly, targeting RGCC in combination with paclitaxel/carboplatin effectively suppresses pulmonary TNBC lung metastasis in a mouse model.

CONCLUSIONS

RGCC overexpression is significantly associated with lung-specific metastasis of TNBC. RGCC activates AMPKα2 and downstream signaling through RGCC-driven PLK1 activity to facilitate TNBC lung metastasis. The study provides implications for RGCC-driven OXPHOS and fatty acid oxidation as important therapeutic targets for TNBC treatment.

Molecular Genetic Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is among the leading causes of irreversible blindness worldwide. In addition to environmental risk factors, such as tobacco use and diet, genetic background has long been established as a major risk factor for the development of AMD. However, our ability to predict disease risk and personalize treatment remains limited by our nascent understanding of the molecular mechanisms underlying AMD pathogenesis. Research into the molecular genetics of AMD over the past two decades has uncovered 52 independent gene variants and 34 independent loci that are implicated in the development of AMD, accounting for over half of the genetic risk. This research has helped delineate at least five major pathways that may be disrupted in the pathogenesis of AMD: the complement system, extracellular matrix remodeling, lipid metabolism, angiogenesis, and oxidative stress response. This review surveys our current understanding of each of these disease mechanisms, in turn, along with their associated pathogenic gene variants. Continued research into the molecular genetics of AMD holds great promise for the development of precision-targeted, personalized therapies that bring us closer to a cure for this debilitating disease.

Targeting the tissue-complosome for curbing inflammatory disease

Hyperactivated local tissue is a cardinal feature of immune-mediated inflammatory diseases of various organs such as the joints, the gut, the skin, or the lungs. Tissue-resident structural and stromal cells, which get primed during repeated or long-lasting bouts of inflammation form the basis of this sensitization of the tissue. During priming, cells change their metabolism to make them fit for the heightened energy demands that occur during persistent inflammation. Epigenetic changes and, curiously, an activation of intracellularly expressed parts of the complement system drive this metabolic invigoration and enable tissue-resident cells and infiltrating immune cells to employ an arsenal of inflammatory functions, including activation of inflammasomes. Here we provide a current overview on complement activation and inflammatory transformation in tissue-occupying cells, focusing on fibroblasts during arthritis, and illustrate ways how therapeutics directed at complement C3 could potentially target the complosome to unprime cells in the tissue and induce long-lasting abatement of inflammation.

High Expression of Complement Component C7 Indicates Poor Prognosis of Breast Cancer and Is Insensitive to Taxane-Anthracycline Chemotherapy

Background

Breast cancer is the most commonly diagnosed cancer worldwide. However, the well-known biomarkers are not enough to meet the needs of precision medicine. Novel targets are desirable and highly valuable for improved patient survival. In this regard, we identified complement component C7 as one of the candidates based on data from the OCOMINE database.

Methods

C7 expression was examined by immunohistochemistry in 331 cases of invasive ductal carcinoma (IDC), 45 cases of ductal carcinoma in situ (DCIS), and 52 cases of non-neoplastic tissues adjacent to tumor. Then, C7 expression was further confirmed by Western blot analysis based on IDC specimens and non-neoplastic breast specimens. The relationship between the C7 expression and prognosis of breast cancer patients was analyzed in order to investigate the function of C7 in breast cancer patients. Meanwhile, we also analyzed the relationship between the C7 expression and prognosis of 149 patients treated with conventional TE (taxane and anthracycline)-based chemotherapy. Then, a cohort of patients (22 cases) treated with TE neoadjuvant chemotherapy was used to further confirm the relationship between the C7 expression and TE-based chemosensitivity.

Results

In our present study, we reported for the first time that C7 was an independent prognostic factor of breast cancer and C7 expression of IDC tissues was higher than non-neoplastic tissues adjacent to tumor and DCIS. In a cohort of 331 IDC patients, high expression of C7 indicated poor prognosis especially in the triple negative subtype and luminal B subtype. Furthermore, C7 was also a promoting factor for triple negative subtype patients to develop bone metastasis. Meanwhile, we provided the first evidence that patients with high C7 expression were insensitive to TE (taxane and anthracycline)-based chemotherapy by analyzing a cohort of 149 patients treated with TE-based chemotherapy and another cohort of 22 patients treated with TE neoadjuvant chemotherapy.

Conclusions

In summary, high expression of C7 may promote breast cancer development and might be insensitive to TE-based chemotherapy. Our present study laid a foundation to help clinicians improve the identification of patients for TE-based chemotherapy by C7 in the era of precision medicine.

Complement and Cancer-A Dysfunctional Relationship?

Although it was long believed that the complement system helps the body to identify and remove transformed cells, it is now clear that complement activation contributes to carcinogenesis and can also help tumors to escape immune-elimination. Complement is activated by several different mechanisms in various types of cancer, and complement activation fragments have multiple different downstream effects on cancer cells and throughout the tumor microenvironment. Thus, the role of complement activation in tumor biology may vary among different types of cancer and over time within a single tumor. In multiple different pre-clinical models, however, complement activation has been shown to recruit immunosuppressive myeloid cells into the tumor microenvironment. These cells, in turn, suppress anti-tumor T cell immunity, enabling the tumor to grow. Based on extensive pre-clinical work, therapeutic complement inhibitors hold great promise as a new class of immunotherapy. A greater understanding of the role of complement in tumor biology will improve our ability to identify those patients most likely to benefit from this treatment and to rationally combine complement inhibitors with other cancer therapies.

Complement System: Promoter or Suppressor of Cancer Progression?

Constituent of innate immunity, complement is present in the tumor microenvironment. The functions of complement include clearance of pathogens and maintenance of homeostasis, and as such could contribute to an anti-tumoral role in the context of certain cancers. However, multiple lines of evidence show that in many cancers, complement has pro-tumoral actions. The large number of complement molecules (over 30), the diversity of their functions (related or not to the complement cascade), and the variety of cancer types make the complement-cancer topic a very complex matter that has just started to be unraveled. With this review we highlight the context-dependent role of complement in cancer. Recent studies revealed that depending of the cancer type, complement can be pro or anti-tumoral and, even for the same type of cancer, different models presented opposite effects. We aim to clarify the current knowledge of the role of complement in human cancers and the insights from mouse models. Using our classification of human cancers based on the prognostic impact of the overexpression of complement genes, we emphasize the strong potential for therapeutic targeting the complement system in selected subgroups of cancer patients.

Oncogenic gene RGC-32 is a direct target of miR-26b and facilitates tongue squamous cell carcinoma aggressiveness through EMT and PI3K/AKT signalling

Growing data have recognized the significance of Response Gene to Complement (RGC)-32 in numerous tumour developments. Notwithstanding, the functional role and underlying mechanism of it in tongue squamous cell carcinoma (TSCC) remain enigmatic. Here, to identify the impact of RGC-32 in TSCC, its expression in multiple TSCC cells was measured and loss-of-function experiments in cell lines were performed to illuminate the function of it induced TSCC progression, via si-RNA knockdown, CCK-8, colony formation, wound-healing, transwell, flow cytometry and western blot assays. To clarify potential mechanism, expressions of hallmarks in epithelial-mesenchymal transition (EMT) process and PI3K/AKT signalling were assessed, and the upstream miR regulator of RGC-32 was predicted and verified by applying bioinformatic approaches and dual-luciferase reporter assay, respectively. Finally, the rescue experiments were applied to better elucidate the effect of miR-26b/RGC-32 axis in TSCC behaviours. As a result, RGC-32 was upregulated in TSCC cells and knocking down of it abrogated cell proliferation, trans-migration and invasion, whilst promoted apoptosis in TSCC, which was regulated through repressing EMT and inactivation of PI3K/AKT signalling. Subsequently, miR-26b was predicted and identified as an upstream regulator of RGC-32, and the pro-tumorigenic effect of RGC-32 was reversed by miR-26b overexpression. Collectively, our results demonstrated that RGC-32 facilitated TSCC progression, which was modulated by activations of PI3K/AKT pathway and EMT process, and reduction of its negative regulator of miR-26b. These findings highlight a novel role of miR-26b/RGC-32 axis in TSCC and underlying mechanism, encouraging a potent usage in TSCC treatment. SIGNIFICANCE OF THE STUDY: We first uncovered that Response Gene to Complement-32 played a significantly pro-tumorigenic role in tongue squamous cell carcinoma (TSCC), which was closely regulated by downregulation of miR-26b and activations of epithelial-mesenchymal transition process and PI3K/AKT signalling. These findings contribute to better understand the molecular mechanism in carcinogenesis of TSCC, and shed some light on promising strategy for TSCC therapeutics.

Functional analyses of rare genetic variants in complement component C9 identified in patients with age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive disease of the central retina and the leading cause of irreversible vision loss in the western world. The involvement of abnormal complement activation in AMD has been suggested by association of variants in genes encoding complement proteins with disease development. A low-frequency variant (p.P167S) in the complement component C9 (C9) gene was recently shown to be highly associated with AMD; however, its functional outcome remains largely unexplored. In this study, we reveal five novel rare genetic variants (p.M45L, p.F62S, p.G126R, p.T170I and p.A529T) in C9 in AMD patients, and evaluate their functional effects in vitro together with the previously identified (p.R118W and p.P167S) C9 variants. Our results demonstrate that the concentration of C9 is significantly elevated in patients' sera carrying the p.M45L, p.F62S, p.P167S and p.A529T variants compared with non-carrier controls. However, no difference can be observed in soluble terminal complement complex levels between the carrier and non-carrier groups. Comparing the polymerization of the C9 variants we reveal that the p.P167S mutant spontaneously aggregates, while the other mutant proteins (except for C9 p.A529T) fail to polymerize in the presence of zinc. Altered polymerization of the p.F62S and p.P167S proteins associated with decreased lysis of sheep erythrocytes and adult retinal pigment epithelial-19 cells by carriers' sera. Our data suggest that the analyzed C9 variants affect only the secretion and polymerization of C9, without influencing its classical lytic activity. Future studies need to be performed to understand the implications of the altered polymerization of C9 in AMD pathology.

Context-dependent roles of complement in cancer

The tumour microenvironment (TME) highly influences the growth and spread of tumours, thus impacting the patient's clinical outcome. In this context, the complement system plays a major and complex role. It may either act to kill antibody-coated tumour cells, support local chronic inflammation or hamper antitumour T cell responses favouring tumour progression. Recent studies demonstrate that these opposing effects are dependent upon the sites of complement activation, the composition of the TME and the tumour cell sensitivity to complement attack. In this Review, we present the evidence that has so far accrued showing a role for complement activation and its effects on cancer control and clinical outcome under different TME contexts. We also include a new analysis of the publicly available transcriptomic data to provide an overview of the prognostic value of complement gene expression in 30 cancer types. We argue that the interplay of complement components within each cancer type is unique, governed by the properties of the tumour cells and the TME. This concept is of critical importance for the design of efficient therapeutic strategies aimed at targeting complement components and their signalling.

Response gene to complement 32 expression in macrophages augments paracrine stimulation-mediated colon cancer progression

M2-polarized tumor associated macrophages (TAMs) play an important role in tumor progression. It has been reported that response gene to complement 32 (RGC-32) promotes M2 macrophage polarization. However, whether RGC-32 expression in macrophages could play a potential role in tumor progression remain unclear. Here we identified that increasing RGC-32 expression in colon cancer and tumor associated macrophages was positively correlated with cancer progression. In vitro studies confirmed that colon cancer cells upregulated RGC-32 expression of macrophages via secreting TGF-β1. RGC-32 expression promoted macrophage migration. In addition, stimulation of HCT-116 cells with the condition mediums of RGC-32-silienced or over-expressed macrophages affected tumor cell colony formation and migration via altered COX-2 expression. In an animal model, macrophages with RGC-32 knockdown significantly decreased the expression of COX-2 and Ki67 in the xenografts, and partly inhibited tumor growth. Together, our results provide the evidences for a critical role of TGF-β1/RGC-32 pathway in TAMs and colon cancer cells during tumor progression.

Role of C5b-9 and RGC-32 in Cancer

The complement system represents an effective arsenal of innate immunity as well as an interface between innate and adaptive immunity. Activation of the complement system culminates with the assembly of the C5b-9 terminal complement complex on cell membranes, inducing target cell lysis. Translation of this sequence of events into a malignant setting has traditionally afforded C5b-9 a strict antitumoral role, in synergy with antibody-dependent tumor cytolysis. However, in recent decades, a plethora of evidence has revised this view, highlighting the tumor-promoting properties of C5b-9. Sublytic C5b-9 induces cell cycle progression by activating signal transduction pathways (e.g., Gi protein/ phosphatidylinositol 3-kinase (PI3K)/Akt kinase and Ras/Raf1/ERK1) and modulating the activation of cancer-related transcription factors, while shielding malignant cells from apoptosis. C5b-9 also induces Response Gene to Complement (RGC)-32, a gene that contributes to cell cycle regulation by activating the Akt and CDC2 kinases. RGC-32 is expressed by tumor cells and plays a dual role in cancer, functioning as either a tumor promoter by endorsing malignancy initiation, progression, invasion, metastasis, and angiogenesis, or as a tumor suppressor. In this review, we present recent data describing the versatile, multifaceted roles of C5b-9 and its effector, RGC-32, in cancer.

Response Gene to Complement 32 in Vascular Diseases

Response gene to complement 32 (RGC32) is a protein that was identified in rat oligodendrocytes after complement activation. It is expressed in most of the organs and tissues, such as brain, placenta, heart, and the liver. Functionally, RGC32 is involved in various physiological and pathological processes, including cell proliferation, differentiation, fibrosis, metabolic disease, and cancer. Emerging evidences support the roles of RGC32 in vascular diseases. RGC32 promotes injury-induced vascular neointima formation by mediating smooth muscle cell (SMC) proliferation and migration. Moreover, RGC32 mediates endothelial cell activation and facilitates atherosclerosis development. Its involvement in macrophage phagocytosis and activation as well as T-lymphocyte cell cycle activation also suggests that RGC32 is important for the development and progression of inflammatory vascular diseases. In this mini-review, we provide an overview on the roles of RGC32 in regulating functions of SMCs, endothelial cells, and immune cells, and discuss their contributions to vascular diseases.

Deacetylase activity-independent transcriptional activation by HDAC2 during TPA-induced HL-60 cell differentiation

The human myeloid leukemia cell line HL-60 differentiate into monocytes following treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). However, the mechanism underlying the differentiation of these cells in response to TPA has not been fully elucidated. In this study, we performed ChIP-seq profiling of RNA Pol II, HDAC2, Acetyl H3 (AcH3), and H3K27me3 and analyzed differential chromatin state changes during TPA-induced differentiation of HL-60 cells. We focused on atypically active genes, which showed enhanced H3 acetylation despite increased HDAC2 recruitment. We found that HDAC2 positively regulates the expression of these genes in a histone deacetylase activity-independent manner. HDAC2 interacted with and recruited paired box 5 (PAX5) to the promoters of the target genes and regulated HL-60 cell differentiation by PAX5-mediated gene activation. Taken together, these data elucidated the specific-chromatin status during HL-60 cell differentiation following TPA exposure and suggested that HDAC2 can activate transcription of certain genes through interactions with PAX5 in a deacetylase activity-independent pathway.

RGC-32 induces transition of pancreatic cancer to epithelial mesenchyme in vivo

OBJECTIVES

This study was undertaken to investigate the induction of transition of pancreatic cancer to epithelial mesenchyme by RGC-32.

METHODS

Primary human pancreatic cancer cell line BXPC-3 was transfected with lentivirus overexpressing the response gene to complement-32 gene (RGC-32) and used to induce tumor in mice. The tumor sizes were measured and the expression of cytokeratin, e-cadherin and vimentin at mRNA using real time PCR and at protein levels by Western blot.

RESULTS

Compared with the control, mice inoculated with the cells transfected with empty vector had similar tumor size while those inoculated with the cells transfected with RGC-32 expressing virus had significantly greater tumor size. HE staining showed that tumors were formed in all treatments. Molecular analyses showed that there was no difference in the expression of the cytokeratin, e-cadherin and vimentin genes at mRNA and protein levels between control and empty vector groups. However, mice derived from cells transfected with RGC-32 expressing virus had reduced cytokeratin and e-cadherin expression and increased vimentin expression.

CONCLUSIONS

These data suggest that RGC-32 promotes the proliferation of pancreatic cancer and induces the epithelial-mesenchymal transition (EMT). It would be a future direction of research to investigate the regulatory mechanism of signal molecules downstream RGC-32 on EMT-related transcription factors and deliberate the role of RGC-32 in tumorigenicity. As a result, RGC-32 may become a new therapeutic target for cancers.

Complement in cancer: untangling an intricate relationship

In tumour immunology, complement has traditionally been considered as an adjunctive component that enhances the cytolytic effects of antibody-based immunotherapies, such as rituximab. Remarkably, research in the past decade has uncovered novel molecular mechanisms linking imbalanced complement activation in the tumour microenvironment with inflammation and suppression of antitumour immune responses. These findings have prompted new interest in manipulating the complement system for cancer therapy. This Review summarizes our current understanding of complement-mediated effector functions in the tumour microenvironment, focusing on how complement activation can act as a negative or positive regulator of tumorigenesis. It also offers insight into clinical aspects, including the feasibility of using complement biomarkers for cancer diagnosis and the use of complement inhibitors during cancer treatment.

The role of complement system in adipose tissue-related inflammation

As the common factor linking adipose tissue to the metabolic context of obesity, insulin resistance and atherosclerosis are associated with a low-grade chronic inflammatory status, to which the complement system is an important contributor. Adipose tissue synthesizes complement proteins and is a target of complement activation. C3a-desArg/acylation-stimulating protein stimulates lipogenesis and affects lipid metabolism. The C3a receptor and C5aR are involved in the development of adipocytes' insulin resistance through macrophage infiltration and the activation of adipose tissue. The terminal complement pathway has been found to be instrumental in promoting hyperglycemia-associated tissue damage, which is characteristic of the major vascular complications of diabetes mellitus and diabetic ketoacidosis. As a mediator of the effects of the terminal complement complex C5b-9, RGC-32 has an impact on energy expenditure as well as lipid and glucose metabolic homeostasis. All of this evidence, taken together, indicates an important role for complement activation in metabolic diseases.

[The complement system: a double edge sword in tumor progression]

The complement system is a key component of the innate immunity, playing a role in pathogen elimination and in host homeostasis. The complement system has been considered for long time as an anti-tumoral element. However, recent studies showed a pro-tumoral effect of complement and particularly of the anaphylatoxines C3a and C5a in a large variety of tumor types. Complement proteins act on different levels of tumor progression, affecting the tumor cells, the angiogenesis and the immune microenvironment. The impact of the complement system on tumor progression seems to be cancer type-dependent and this has to be taken into account in the establishment of potential biomarkers and development of therapeutic strategies.

C5b-9 Staining Correlates With Clinical and Tumor Stage in Gastric Adenocarcinoma

The complement system is a critical part of the immune response, acting in defense against viral infections, clearance of immune complexes, and maintenance of tissue homeostasis. Upregulated expression of the terminal complement complex, C5b-9, has been observed on various tumor cells, such as stomach carcinoma cells, and on cells in the necrotic regions of these tumors as well; however, whether and how C5b-9 is related to gastric cancer progression and severity remains unknown. In this study, human gastric adenocarcinoma (HGAC) tissues (n=47 cases) and patient-matched adjacent nontumoral parenchyma (n=20 cases) were evaluated by tissue microarray and immunohistochemistry. The HGAC tissues showed upregulated C5b-9 expression. Multinomial logistic regression and likelihood ratio testing showed that overexpression of C5b-9 in HGAC tissue was significantly correlated with clinical stage (P=0.007) and tumor stage (P=0.005), but not with tumor distant organ metastasis, lymphoid nodal status, sex, or age. Patients with late-stage gastric adenocarcinoma had a higher amount of tumor cells showing positive staining for C5b-9 than patients with early-stage disease. These results may help in diagnosis and assessment of disease severity of human gastric carcinoma.

C1q acts in the tumour microenvironment as a cancer-promoting factor independently of complement activation

Complement C1q is the activator of the classical pathway. However, it is now recognized that C1q can exert functions unrelated to complement activation. Here we show that C1q, but not C4, is expressed in the stroma and vascular endothelium of several human malignant tumours. Compared with wild-type (WT) or C3- or C5-deficient mice, C1q-deficient (C1qa^−/−) mice bearing a syngeneic B16 melanoma exhibit a slower tumour growth and prolonged survival. This effect is not attributable to differences in the tumour-infiltrating immune cells. Tumours developing in WT mice display early deposition of C1q, higher vascular density and an increase in the number of lung metastases compared with C1qa^−/− mice. Bone marrow (BM) chimeras between C1qa^−/− and WT mice identify non-BM-derived cells as the main local source of C1q that can promote cancer cell adhesion, migration and proliferation. Together these findings support a role for locally synthesized C1q in promoting tumour growth.

C1q is known to initiate the activation of the complement classical pathway. Here, the authors show the C1q is expressed in the tumour microenvironment and can promote cancer cell migration and adhesion in a complement activation-independent manner.

Role of SIRT1 in autoimmune demyelination and neurodegeneration

Multiple sclerosis (MS) is a demyelinating disease characterized by chronic inflammation of the central nervous system, in which many factors can act together to influence disease susceptibility and progression. SIRT1 is a member of the histone deacetylase class III family of proteins and is an NAD(+)-dependent histone and protein deacetylase. SIRT1 can induce chromatin silencing through the deacetylation of histones and plays an important role as a key regulator of a wide variety of cellular and physiological processes including DNA damage, cell survival, metabolism, aging, and neurodegeneration. It has gained a lot of attention recently because many studies in animal models of demyelinating and neurodegenerative diseases have shown that SIRT1 induction can ameliorate the course of the disease. SIRT1 expression was found to be decreased in the peripheral blood mononuclear cells of MS patients during relapses. SIRT1 represents a possible biomarker of relapses and a potential new target for therapeutic intervention in MS. Modulation of SIRT1 may be a valuable strategy for treating or preventing MS and neurodegenerative central nervous system disorders.

Complement the hemostatic system: an intimate relationship

The complement system is important part of our innate immune system and interacts directly with the hemostatic system. Disorders of complement activation or dysregulation resulting in excess complement generation, such as Paroxysmal Nocturnal Hemoglobinuria (PNH), atypical Hemolytic uremic Syndrome (aHUS) and antiphospholipid syndrome (APLS) have been associated with significant thrombophilia. Terminal Complement (C5b-9) deposition on endothelial and tumor cell membranes has also been reported in a variety of cancer. Recent developments in complement inhibition have given us new insights into the mechanism of thrombosis in these disorders.

The role of complement in tumor growth

Complement is a central part of the immune system that has developed as a first defense against non-self cells. Neoplastic transformation is accompanied by an increased capacity of the malignant cells to activate complement. In fact, clinical data demonstrate complement activation in cancer patients. On the basis of the use of protective mechanisms by malignant cells, complement activation has traditionally been considered part of the body's immunosurveillance against cancer. Inhibitory mechanisms of complement activation allow cancer cells to escape from complement-mediated elimination and hamper the clinical efficacy of monoclonal antibody-based cancer immunotherapies. To overcome this limitation, many strategies have been developed with the goal of improving complement-mediated effector mechanisms. However, significant work in recent years has identified new and surprising roles for complement activation within the tumor microenvironment. Recent reports suggest that complement elements can promote tumor growth in the context of chronic inflammation. This chapter reviews the data describing the role of complement activation in cancer immunity, which offers insights that may aid the development of more effective therapeutic approaches to control cancer.

Complement inhibition in cancer therapy

For decades, complement has been recognized as an effector arm of the immune system that contributes to the destruction of tumor cells. In fact, many therapeutic strategies have been proposed that are based on the intensification of complement-mediated responses against tumors. However, recent studies have challenged this paradigm by demonstrating a tumor-promoting role for complement. Cancer cells seem to be able to establish a convenient balance between complement activation and inhibition, taking advantage of complement initiation without suffering its deleterious effects. Complement activation may support chronic inflammation, promote an immunosuppressive microenvironment, induce angiogenesis, and activate cancer-related signaling pathways. In this context, inhibition of complement activation would be a therapeutic option for treating cancer. This concept is relatively new and deserves closer attention. In this article, we summarize the mechanisms of complement activation on cancer cells, the cancer-promoting effect of complement initiation, and the rationale behind the use of complement inhibition as a therapeutic strategy against cancer.

Complement in animal development: unexpected roles of a highly conserved pathway

The complement pathway is most famous for its role in immunity, orchestrating an exquisitely refined system for immune surveillance. At its core lies a cascade of proteolytic events that ultimately serve to recognise microbes, infected cells or debris and target them for elimination. Mounting evidence has shown that a number of the proteolytic intermediaries in this cascade have, in themselves, other functions in the body, signalling through receptors to drive events that appear to be unrelated to immune surveillance. It seems, then, that the complement system not only functions as an immunological effector, but also has cell-cell signalling properties that are utilised by a number of non-immunological processes. In this review we examine a number of these processes in the context of animal development, all of which share a requirement for precise control of cell behaviour in time and space. As we will see, the scope of the complement system's function is indeed much greater than we might have imagined only a few years ago.