title: Binding of alpha2ML1 to the low density lipoprotein receptor-related protein 1 (LRP1) reveals a new role for LRP1 in the human epidermis.
abstract: BACKGROUND
  The multifunctional receptor LRP1 has been shown to bind and internalize a large number of protein ligands with biological importance such as the pan-protease inhibitor alpha2-macroglobulin (alpha2M). We recently identified Alpha2ML1, a new member of the alpha2M gene family, expressed in epidermis. alpha2ML1 might contribute to the regulation of desquamation through its inhibitory activity towards proteases of the chymotrypsin family, notably KLK7. The expression of LRP1 in epidermis as well as its ability to internalize alpha2ML1 was investigated.
  
  
  RESULTS
  In human epidermis, LRP1 is mainly expressed within the granular layer of the epidermis, which gathers the most differentiated keratinocytes, as shown by immunohistochemistry and immunofluorescence using two different antibodies. By using various experimental approaches, we show that the receptor binding domain of alpha2ML1 (RBDl) is specifically internalized into the macrophage-like cell line RAW and colocalizes with LRP1 upon internalization. Coimmunoprecipitation assays demonstrate that RBDl binds LRP1 at the cell surface. Addition of RAP, a universal inhibitor of ligand binding to LRP1, prevents RBDl binding at the cell surface as well as internalization into RAW cells. Silencing Lrp1 expression with specific siRNA strongly reduces RBDl internalization.
  
  
  CONCLUSIONS
  Keratinocytes of the upper differentiated layers of epidermis express LRP1 as well as alpha2ML1. Our study also reveals that alpha2ML1 is a new ligand for LRP1. Our findings are consistent with endocytosis by LRP1 of complexes formed between alpha2ML1 and proteases. LRP1 may thus control desquamation by regulating the biodisponibility of extracellular proteases.
authors.affiliation: UMR5165 UDEAR-CNRS/UPS, CHU PURPAN, Toulouse, France.
authors.forename: Marie-Florence
authors.initials: MF
authors.lastname: Galliano
authors.forename: Eve
authors.initials: E
authors.lastname: Toulza
authors.forename: Nathalie
authors.initials: N
authors.lastname: Jonca
authors.forename: Steven L
authors.initials: SL
authors.lastname: Gonias
authors.forename: Guy
authors.initials: G
authors.lastname: Serre
authors.forename: Marina
authors.initials: M
authors.lastname: Guerrin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002918:Chymotrypsin / Q000737:chemistry; D004705:Endocytosis; D004817:Epidermis / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D026563:LDL-Receptor Related Protein-Associated Protein / Q000378:metabolism* / Q000502:physiology*; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C510358:A2ML1 protein, human; D026563:LDL-Receptor Related Protein-Associated Protein; D000511:alpha-Macroglobulins; D002918:Chymotrypsin