K562 erythroleukemic cells are equipped with multiple mechanisms of resistance to lysis by complement

Abstract

Resistance of tumor cells to lysis by complement is generally attributed to several protective mechanisms. The relative impact of these mechanisms in the same tumor cell, however, has not been assessed yet. We have analyzed the interaction of the human erythroleukemia tumor cell line K562 with human complement. K562 cells express the membrane complement regulatory proteins CD59, CD55 and CD46. As shown here for the first time, K562 also spontaneously release the soluble regulators C1 inhibitor, factor H, and soluble CD59. Complement resistance of K562 cells is augmented upon treatment with PMA, TNF or even with sublytic complement. Unlike TNF and sublytic complement, PMA enhanced the expression of membrane-bound CD55 and CD59 and led to increased secretion of soluble CD59. In addition, we show that complement-resistant K562 cells express a membrane-associated proteolytic activity, higher than the complement-sensitive K562/S cells. Treatment of complement-resistant K562 cells with serine protease inhibitors enhance their sensitivity to complement-mediated lysis. Inhibitors of protein kinase C (PKC) also sensitize K562 cells to complement lysis, implicating PKC-mediated signaling in cell resistance to complement. Neutralization of the CD55 and CD59 but not of CD46 regulatory activity with specific antibodies significantly increases complement-mediated K562 cell lysis. Treatment of K562 cells with a mixture of inhibitory reagents results in a significant additive enhancing effect on complement-mediated lysis of K562. In conclusion, K562 cells resist a complement attack by concomitantly using multiple molecular evasion strategies. Future attempts in antibody-based tumor therapy should include strategies to interfere with those resistance mechanisms.

Mouse Complement Receptor-Related Gene y/p65-Neutralized Tumor Vaccine Induces Antitumor Activity In Vivo

“…In humans, complement-regulatory proteins are overexpressed on many kinds of tumor cells and tumor cell lines, and their expression prevents homologous complement attack in vitro (11)(12)(13)(14)(15)(16). The ability of complement-regulatory proteins to protect tumor cells from complement, and the ability of anti-complement regulator neutralizing mAbs to sensitize tumor cells to complement have been extensively studied in vitro (17, 34 -38).…”

Interference with the Complement System by Tumor Cell Membrane Type-1 Matrix Metalloproteinase Plays a Significant Role in Promoting Metastasis in Mice

“…This event initiates the complement activation cascade and results in the generation of anaphylatoxins (C3a, C4a, and C5a) and cytolytic C5b-9 membrane attack complex (5). Tumor cells frequently overexpress the specialized cell surface-associated proteins, including the proteases, to inhibit the complement propagation and thus to protect themselves against the complement-mediated cytolysis (6)(7)(8)(9)(10)(11)(12)(13).…”

Extracellular phosphorylation of C9 by protein kinase CK2 regulates complement-mediated lysis

“…For protection against accidental death, all cells are equipped with an array of complement inhibitors. These include the membrane complement regulators CD46, CD55 and CD59 [4], ectoproteases [2,5], sialic acid residues [3,6] and intracellular damage repair mechanisms [7][8][9]. The protective impact of the ecto-CK2 relative to other complement inhibitors is not known.…”

“…This is largely due to expression of several defense mechanisms, some inhibiting complement activation and others promoting cell resistance to death (reviewed in [1]). The various mechanisms act in an additive manner to produce the complement-resistant phenotype [2,3]. First line defense is provided by the membrane complement regulatory proteins CD46 (membrane cofactor protein/MCP), CD55 (decay-accelerating factor/DAF) and CD59 (reviewed in [4]).…”

“…These regulatory proteins are overexpressed in many tumors and are even secreted into the tumor microenvironment. Additional protection may be conferred by ecto-proteases that cleave cell-bound complement components [2,5] and by sialic acid-rich macromolecules at the cell surface [3,6]. Beyond these extracellular resistance molecules, cells utilize intracellular resistance mechanisms that are still elusive but are known to be dependent on complementinduced calcium influx, activation of PKC and ERK [7,8], and heat shock proteins [9,10].…”