Expression of complement regulator proteins in primary and metastatic malignant melanoma

CD59: a promising target for tumor immunotherapy

CD59 has been identified as a glycosylphosphatidylinositol-anchored membrane protein that acts as an inhibitor of the formation of the membrane attack complex to regulate complement activation. Recent studies have shown that CD59 is highly expressed in several cancer cell lines and tumor tissues. CD59 also regulates the function, infiltration and phenotypes of a variety of immune cells in the tumor microenvironment. Herein, we summarized recent advances related to the functions and mechanisms of CD59 in the tumor microenvironment. Therapeutic strategies that seek to modulate the functions of CD59 in the tumor microenvironment could be a promising direction for tumor immunotherapy.

Bioinformatic analysis of the membrane cofactor protein CD46 and microRNA expression in hepatocellular carcinoma

The therapeutic potential of membrane complement regulatory protein (mCRP)-neutralizing antibodies is unsatisfactory, which perhaps lies in the complex role of mCRPs in tumor occurrence and development. As a member of the mCRPs, CD46 is a transmembrane protein with a cytoplasmic domain and is implicated more in the control of the alternative complement pathway than of the classical complement pathway. Growing evidence has revealed that both the CD46 signaling pathway and microRNAs (miRNAs) play an important role in the development and progression of hepatocellular carcinoma (HCC). In the present study, we analyzed mCRP expression in different tumor tissues by employing western blotting and qPCR. To address the potential role of miRNAs in CD46 signaling, we set out to profile miRNA expression in CD46-overexpressed and -silenced HepG2 cell lines. Furthermore, bioinformatic analysis was performed to identify downstream targets of CD46 signaling. We found that the levels of CD46 expression in HCC tissues were significantly higher compared to that in the adjacent normal tissues. After complement-related gene expression profiling and unsupervised hierarchical clustering analysis of 10 HCC tissues, a total of 37 miRNAs showed significantly different expression levels before and after CD46 expression change. By bioinformatic analysis, we identified let-7b and miR-17 as downstream targets of CD46 signaling, and that the expression levels of let-7b and miR-17 were negatively correlated with that of CD46 in HepG2 cells. The present study suggests that CD46 plays an important role in HCC carcinogenesis by regulating let-7b and miR-17.

Anti-alphaGal-dependent complement-mediated cytotoxicity in metastatic melanoma

Antibodies to the cell surface disaccharide galactose(alpha1,3)galactose (alphaGal) are the most prevalent natural antibodies in human serum. The anti-alphaGal immunoglobulin M-dependent activation of complement causes hyperacute rejection of organ transplants from discordant species by human recipients. It has been shown in vitro that human tumour cells transduced with the gene that synthesizes alphaGal become sensitive to human serum. A prerequisite for anti-alphaGal antibody-based therapeutic strategies is that patients with cancer have adequate serum levels of anti-alphaGal immunoglobulins and complement. The objective of this work was to measure the levels and function of anti-alphaGal immunoglobulins and complement in the serum of patients with metastatic melanoma and healthy volunteers. Serum complement levels were assayed by radial immunodiffusion. Anti-alphaGal immunoglobulin G and immunoglobulin M titres were measured by enzyme-linked immunosorbent assay. Disaccharide sugar blocking was used to investigate antibody specificity. The functional integrity of anti-alphaGal antibodies and complement was investigated in cell lysis assays. It was found that the levels of the complement components C1q, C3 and C4 and the function of the classical complement pathway were normal in metastatic melanoma patients. Anti-alphaGal antibody titres were as variable in metastatic melanoma patients as in healthy controls, and the lysis of alphaGal-expressing cells correlated with anti-alphaGal immunoglobulin M titre (P < 0.0001). Anti-alphaGal antibody titres, complement levels and overall cytolytic function in the serum of patients with metastatic melanoma were indistinguishable from those of healthy controls. There is thus nothing intrinsic to the disease that will limit anti-alphaGal-based therapeutic strategies for enhanced antigen presentation or induced cell lysis, including the mimicry of hyperacute rejection.