Truncated and chimeric HMGI-C genes induce neoplastic transformation of NIH3T3 murine fibroblasts

Overexpression of the high mobility group I (HMGI) proteins is often associated with the malignant pheno- type. Moreover, many benign human tumors, mainly of mesenchymal origin, are characterized by rearrange- ments of the HMGI-C gene. In most cases, HMGI-C alterations involve breaks within the third intron of the gene resulting in aberrant transcripts carrying exons from 1 ± 3, which encode the three DNA binding domains, fused to ectopic sequences. Here, we show that the expression of a truncated form of HMGI-C protein carrying only the three DNA-binding domains, or of a fusion protein carrying the three DNA-binding domains of HMGI-C and the LIM domains of the lipoma preferred partner gene (LPP) protein, causes malignant transformation of NIH3T3 cells. The unrearranged wild- type HMGI-C cDNA did not exert any transforming activity. These ®ndings indicate that rearranged forms of HMGI-C play a role in cell transformation.