ANEMIA-INDUCING FACTOR EXPRESSED IN GASTRIC-CANCER IS HOMOLOGOUS WITHCOMPLEMENT REGULATORY FACTOR CD59

Anemia-inducing factor (AIF) was isolated from gastric cancer tissue; however, the human placenta used as the volume of AIF for further anal ysis did not prove sufficient. This substance was named placental anem ia-inducing factor (PAIF). PAIF directly reduces the number of erythro cytes in vitro and reduces the RBC count in rabbits to 80% when i.v, a dministration of 27 mu g/kg of body weight is given. The aim of this s tudy is to better define PAIF and to examine whether the identifical s ubstance expresses on either the surface or in the cytoplasm of establ ished gastric cancer eel lines. PAIF is a glycoprotein with about 20 K D, whose 17 amino acid residues of N terminus were sequenced after Edm an treatment. The N-terminus of PAIF were determined as Lqcyncpnptadck tav. This is homologous with that of CD59, which is thought as a regul ator of membrane attack complex of complement system. Expression of PA F or CD59 in four established gastric cancer cell Lines were examined by indirect immunofluorescence method and by Northen blot hybridizatio n. The cells (1 x 10(6)) were seeded into plastic plates for three day s and reacted overnight at 4 degrees C in 0.5 ml of PBS with anti-PAIF polyclonal antibody or with anti CD59 rat monoclonal antibody. Both P AIF and CD59 were stained positively on the surface and/or in the cyro plasm. The total RNAs were prepared from the four kinds of cell lines and normal human lymphocytes. CD59 mRNA was probed in all cell lines b y BamH1-EcoR1 fragment of PSRa CD59. The signal levels of MKN-28, MKN- 45 and KATO-III were stronger than that of MKN-74, whereas the signal of normal lymphocytes was the lowest. Although there is no decisive ev idence that PAIF is exactly the same substance as CD59, and although t he biological functions of these two subastances are conflictive, and still to be further investigated, the 17 amino acid residues of N-term inus of PAIF expressed in gastric cancer cells were homologous with th oese of CD59. A derivative of CD59 may exist in gastric cancer.