Secretion of soluble complement inhibitors factor H and factor H-like protein (FHL-1) by ovarian tumour cells

Abstract

We observed that the soluble complement regulators factor H and factor H-like protein were abundantly present in ascites samples as well as in primary tumours of patients with ovarian cancer. RT -PCR and immunoblotting analyses showed that the two complement inhibitors were constitutively produced by the ovarian tumour cell lines SK-OV-3 and Caov-3, but not PA-1 or SW626 cells. The amounts of factor H-like protein secreted were equal to those of factor H. This is exceptional, because e.g. in normal human serum the concentration of factor H-like protein is below 1/10th of that of factor H. In ascites samples the mean level of factor H-like protein (130+55 mg ml 71 ) was 5.5-fold higher than in normal human serum (24+3 mg ml 71 ). Ovarian tumour cells thus preferentially synthesise factor H-like protein, the alternatively spliced short variant of factor H. The tumour cells were found to bind both 125 I-labelled factor H and recombinant factor H-like protein to their surfaces. Surprisingly, the culture supernatants of all of the ovarian tumour cell lines studied, including those of PA-1 and SW626 that did not produce factor H/factor H-like protein, promoted factor I-mediated cleavage of C3b to inactive iC3b. Subsequently, the PA-1 and SW626 cell lines were found to secrete a soluble form of the membrane cofactor protein (CD46). Thus, our studies reveal two novel complement resistance mechanisms of ovarian tumour cells: (i) production of factor H-like protein and factor H and (ii) secretion of soluble membrane cofactor protein. Secretion of soluble complement inhibitors could protect ovarian tumour cells against humoral immune attack and pose an obstacle for therapy with monoclonal antibodies.

The dual role of complement in cancer and its implication in anti-tumor therapy

“…Like most mCRPs, it is expressed on various tumors including head and neck squamous cell carcinoma (HNSCC) (102), hematological malignancies (93,103), breast, prostate (104), ovarian (105,106), glioma (107), liver (108), renal (25) and cervical cancer (109) among others. Together with CD55, downregulation of CD46 with siRNA resulted in increased CDC in a number of cell lines (99,110).…”

“…It binds to C3b, thereby preventing subsequent formation of the lytic components at the cell surface. Resistance to factor H-mediated complement attack was found to be significant in ovarian cancer cells, lung cancer and glioblastoma cells (106,(120)(121)(122). Moreover, the monoclonal antibody cetuximab had significantly higher activity on A549 cells, in which factor H was genetically downregulated with siRNA (122,123).…”

Regulation of complement and modulation of its activity in monoclonal antibody therapy of cancer

“…The secretion of sCRPs or the upregulation of membrane-bound CRPs (mCRPs) in cancer was shown for nearly all CRPs. Secretion of the sCRP Factor H and its splice variant FHL-1 was shown for primary tumor cells and cancer cell lines, including ovarian cancer cells, 24 lung tumor cells, 25 and colon cancer cells. 26 High levels of the sCRP clusterin are found in several human cancers [27][28][29][30] compared with normal tissues with some exceptions.…”

Complement factor H-derived short consensus repeat 18-20 enhanced complement-dependent cytotoxicity of ofatumumab on chronic lymphocytic leukemia cells

“…and tumor cell lines (H2 glioblastoma cells) against CDC. [19][20][21] fH is a 155-kDa single polypeptide chain glycoprotein that is present in plasma at a concentration of 0.235-0.81 mg/mL. 22,23 Its mode of action is at the level of complement convertases, whereby fH accelerates the decay of alternative pathway (AP) C3 and C5 convertase.…”