Aminoacyl-transfer ribonucleic acid (tRNA) synthetases-interacting multifunctional protein (AIMP) 2 is a factor associated with the macromolecular protein synthesis machinery consisting of nine different aminoacyl-tRNA synthetases and three non-enzymatic factors. However, it was shown to work as a multifaceted regulator through the versatile interactions with diverse signal mediators. For instance, it can mediate pro-apoptotic response to DNA damage and tumor necrosis factor-alpha (TNF-alpha) stimulus and growth-arresting signal by transforming growth factor (TGF)-beta. Considering that these pathways are critically implicated in the control of tumorigenesis, AIMP2 is expected to work as a potent tumor suppressor with broad coverage against different cancer types. Here we investigated whether AIMP2 would give gene dosage effect on its pro-apoptotic and anti-proliferative activities using the wild-type, hetero- and homozygous AIMP2 cells and whether AIMP2 would be critical in preventing tumorigenesis using different in vivo tumor models. Both the apoptotic responses to DNA damage and TNF-alpha and sensitivity to growth arresting TGF-beta signal were reduced in AIMP2 hetero- and homozygous cells compared with the wild-type cells in dose-dependent manner. In all the in vivo carcinogenesis experiments, reduction of AIMP2 level in heterozygous AIMP2 mice provided higher susceptibility to tumor formation. Thus, this work proves the functional significance of AIMP2 in determination of cell proliferation and death, and as a haploinsufficient tumor suppressor.