Interaction of HRP-2 isoforms with HDGF: chromatin binding of a specific heteromer.

Hepatoma-derived growth-factor-related protein 2 (HRP-2) belongs to a family with five additional members: hepatoma-derived growth factor (HDGF); lens epithelium-derived growth factor; and the HDGF-related proteins -1, -3 and -4. Very little is known regarding the function of HRP-2 in particular. This study shows for the first time heteromer formation of different members of the HRP family; HDGF and HRP-2. In addition, we discovered a previously unknown splice variant of HRP-2 mRNA encoding for a protein with a 53-amino acid deletion in its hath region. This HRP-2 isoform c interacts preferentially with a processed form of HDGF probably because of the loss of an α helix of HRP-2. Furthermore, in contrast to other isoforms of HRP-2, isoform c binds to chromatin similar to its most closely related family member lens epithelium-derived growth factor with potential consequences regarding its function in HIV integration. Interestingly, only the new HRP-2 isoform c and a processed form of HDGF are displaced from condensed mitotic metaphase chromatin. In conclusion, these observations provide a new perspective for understanding the biological functions of HDGF and related proteins.