Aminoacyl-tRNA synthetase-interacting multi-functional protein 2 (AIMP2) works as potent tumor suppressor, while its splicing variant lacking exon 2 (AIMP2-DX2) competes with AIMP2 for binding to target proteins and compromises its anti-tumor activity. Assuming that AIMP2 and its variant AIMP2-DX2 could be released out to human sera in pathological condition, we investigated the diagnostic and prognostic usefulness of autoantibodies against AIMP2 and AIMP2-DX2 by measuring their serum levels in 80 normal and lung cancer samples that were matched in age, gender and smoking status. The area under the curve of AIMP2-DX2, AIMP2, and AIMP2-DX2/AIMP2 autoantibody ratio was low (0.416, 0.579, and 0.357, respectively), suggesting limited diagnostic value. A total of 165 lung cancer patients were classified into low and high AIMP2-DX2, AIMP2, and AIMP2-DX2/AIMP2 based on the median expression of each parameter. The high AIMP2-DX2 group was older and had larger tumors (>3 cm) than the low AIMP2-DX2 group. The high AIMP2-DX2/AIMP2 group had higher CYFRA-21 levels and significantly shorter overall survival than the low AIMP2-DX2/AIMP2 group (18.6 vs. 48.9 months, P = 0.021, Log Rank Test). Taken together, autoantibodies against AIMP2-DX2 and AIMP2 are detectable in the human blood and the increased ratio of AIMP2-DX2/AIMP2 is related to poor clinical outcome of lung cancer.

AIMP2-DX2, an exon 2-deleted splice variant of AIMP2 (aminoacyl-tRNA synthetase-interacting multifunctional protein 2), is highly expressed in lung cancer and involved in tumor progression in vivo. Oncogenic function of AIMP2-DX2 and its correlation with poor prognosis of cancer patients have been well established; however, the application of this potentially important biomarker to cancer research and diagnosis has been hampered by a lack of antibodies specific for the splice variant, possibly due to the poor immunogenicity and/or stability of AIMP2-DX2. In this study a monoclonal antibody, H5, that specifically recognizes AIMP2-DX2 and its isoforms was generated via rabbit immunization and phage display techniques, using a short peptide corresponding to the exon 1/3 junction sequence as an antigen. Furthermore, based on mutagenesis, limited cleavage, and mass spectrometry studies, it is also suggested that the endogenous isoform of AIMP2-DX2 recognized by H5 is produced by proteolytic cleavage of 33 amino acids from N-terminus and is capable of inducing cell proliferation similarly to the uncleaved protein. H5 monoclonal antibody is applicable to enzyme-linked immunosorbent assay, immunoblot, immunofluorescence, and immunohistochemistry, and expected to be a valuable tool for detecting AIMP2-DX2 with high sensitivity and specificity for research and diagnostic purposes.