Extracellular Heat Shock Protein 90 Signals through Subdomain II and the NPVY Motif of LRP-1 Receptor to Akt1 and Akt2: a Circuit Essential for Promoting Skin Cell Migration In Vitro and Wound Healing In Vivo

Normal cells secrete heat shock protein 90 alpha (Hsp90 alpha) in response to tissue injury. Tumor cells have managed to constitutively secrete Hsp90 alpha during invasion and metastasis. The sole function of extracellular Hsp90 alpha (eHsp90 alpha) is to promote cell motility, a critical event for both wound healing and tumor progression. The mechanism of promotility action by eHsp90 alpha, however, has remained elusive. A key issue is whether eHsp90 alpha still acts as a chaperone outside the cells or is a new and bona fide signaling molecule. Here, we have provided evidence that eHsp90 alpha utilizes a unique transmembrane signaling mechanism to promote cell motility and wound healing. First, subdomain II in the extracellular part of low-density lipoprotein receptor-related protein 1 (LRP-1) receives the eHsp90 alpha signal. Then, the NPVY but not the NPTY motif in the cytoplasmic tail of LRP-1 connects eHsp90 alpha signaling to serine 473 but not threonine 308 phosphorylation in Akt kinases. Individual knockdown of Akt1, Akt2, or Akt3 revealed the importance of Akt1 and Akt2 in eHsp90 alpha-induced cell motility. Akt gene rescue experiments suggest that Akt1 and Akt2 work in concert, rather than independently, to mediate eHsp90 alpha promotility signaling. Finally, Akt1 and Akt2 knockout mice showed impaired wound healing that cannot be corrected by topical application with the eHsp90 alpha protein.