Structural and functional properties of complement-activating protein M161Ag, a Mycoplasma fermentans gene product that induces cytokine production by human monocytes.
Human malignant cells are targeted by homologous complement C3b if they express M161Ag, a 43-kDa protein with C3-activating property. cDNA of M161Ag cloned from human leukemia cell lines predicted M161Ag as a novel secretory protein comprised of 428 amino acids including 5 amino acids encoded by TGA codons (Matsumoto M., Takeda, J., Inoue, N., Hara, T., Hatanaka, M., Takahashi, K., Nagasawa, S., Akedo, H., and Seya, T. (1997) Nat. Med. 3, 1266-1270), although the origin of this gene was obscure. Here we clarified this point through genomic and biochemical analysis: 1) 5'-UT and genomic sequences represented the prokaryote promoter and ribosomal binding site; 2) the TGA codons in M161Ag cDNA were translated not into selenocysteines but into tryptophans; 3) M161Ag anchored onto the membrane secondary to its N-terminal palmitoylation like prokaryote lipoproteins; 4) genomic and cDNA clones of M161Ag were highly homologous to Mycoplasma fermentans gene encoding P48, a monocytic differentiation/activation factor, recently released in the data base, although the resultant proteins were different in the amino acid sequences. Additionally, purified soluble M161Ag efficiently provoked IL-1beta, tumor necrosis factor alpha, and IL-6 like P48, and further IL-10 and IL-12 in human peripheral blood monocytes. Thus, M161Ag originates from M. fermentans, and latently infected M. fermentans allows human cells to produce M161Ag. The liberated protein serves as a potent modulator of innate and cellular immune responses via its complement-activating and cytokine-producing activities.
Matsumoto
M
M
Department of Immunology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Higashinari-ku, Osaka 537, Japan.
Nishiguchi
M
M
Kikkawa
S
S
Nishimura
H
H
Nagasawa
S
S
Seya
T
T
D000595:Amino Acid Sequence; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D003167:Complement Activation; D003170:Complement Pathway, Alternative; D004247:DNA; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism*; D016858:Mycoplasma fermentans / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D014407:Tumor Cells, Cultured
C091221:M161 antigen; D008565:Membrane Proteins; D004247:DNA