MOLECULAR-CLONING OF THE 31-KDA CYTOSOLIC PHOSPHOLIPASE-A(2), AS AN ANTIGEN RECOGNIZED BY THE LUNG CANCER-SPECIFIC HUMAN MONOCLONAL-ANTIBODY, AE6F4

The human monoclonal antibody AE6F4 specifically reacts with human lung cancer tissues but does not with normal tissues. This monoclonal antibody recognizes a cytosolic 31 kDa antigen in the cancer cells. In a previous study, we elucidated that the 31 kDa antigen belonged to a family of proteins collectively designated as 14-3-3 proteins, which were known as protein kinase-dependent activators of tyrosine/trytophan hydroxylases, or protein kinase C inhibitor proteins. Here we report molecular cloning of the 31 kDa antigen from the human lung adenocarcinoma cell line, A549. Sequencing analysis indicates that the cloned cDNA is identical to that of previously reported human placental cytosolic phospholipase Az (cPLA(2)), which is also a member of the 14-3-3 protein family. Western analysis demonstrated that a 31 kDa recombinant cPLA(2) expressed in monkey COS cells was recognized by the AE6F4 monoclonal antibody. Binding of the monoclonal antibody to the recombinant cPLA(2) was abolished when treated with sodium periodate, suggesting that not only are carbohydrate chains associated with the cPLA(2), but they also play a crucial role in antigen recognition by the monoclonal antibody.