The nuclear architectural protein HMGA1a triggers receptor‐mediated endocytosis

High mobility group proteins A (HMGA), nuclear architectural factors, locate in the cell nuclei and mostly execute gene‐regulation function. However, our results reveal that a HMGA member (HMGA1a) has a unique plasma membrane receptor; this receptor specifically binds to HMGA‐decorated species, effectively mediates endocytosis, and internalizes extracellular HMGA‐functionalized cargoes. Indeed, dyes or nanoparticles labeled with HMGA1a protein readily enter Hela cells. Using a stratagem chemical cross‐linker, we covalently bonded the HMGA receptor to the HMGA1a‐GFP fusion protein, thus capturing the plasma membrane receptor. Subsequent Western blots and SDS–PAGE gel revealed that the HMGA receptor is a 26‐kDa protein. Confocal live‐cell microscopic imaging was used to monitor the whole endocytic process, in which the internalized HMGA1a‐decorated species are transported by motor proteins on microtubules and eventually arrive at the late endosomes/lysosomes. Cell viability assays also suggested that extracellular HMGA1a protein directly influences the survival ability of Hela cells in a dose‐dependent manner, implying versatility of HMGA1a protein and its potent role to suppress cancer cell survivability and to regulate growth. J. Cell. Biochem. 108: 791–801, 2009. © 2009 Wiley‐Liss, Inc.