Overexpression of HMGA2-LPP Fusion Transcripts Promotes Expression of the Alpha 2 Type XI Collagen Gene

In a subset of human lipomas, a specific t(3;12) chromosome translocation gives rise to HMGA2-LPP fusion protein, containing the amino (N)-terminal DNA binding domains of HMGA2 fused to the carboxyl (C)-terminal LIM domains of LPP. In addition to its role in adipogenesis, several observations suggest that HMGA2-LPP is linked to chondrogenesis. Here, we analyzed whether HMGA2-LPP promotes chondrogenic differentiation, a marker of which is transactivation of the alpha 2 type XI collagen gene (Col11a2). Real-time PCR analysis showed that HMGA2-LPP and COL11A2 were co-expressed. Luciferase assay demonstrated that either of HMGA2-LPP, wild-type HMGA2 or the N-terminal HMGA2 transactivated the Col11a2 promoter in HeLa cells, while the C-terminal LPP did not. RT-PCR analysis revealed that HMGA2-LPP transcripts in lipomas with the fusion were 591-fold of full-length HMGA2 transcripts in lipomas without the fusion. These results indicate that in vivo overexpression of HMGA2-LPP promotes chondrogenesis by upregulating cartilage-specific collagen gene expression through the N-terminal DNA binding domains.