title: HAI-1 regulates activation and expression of matriptase, a membrane-bound serine protease.
abstract: Hepatocyte growth factor activator inhibitor-1 (HAI-1) was initially identified as cognate inhibitor of matriptase, a membrane-bound serine protease. Paradoxically, HAI-1 is also required for matriptase activation, a process that requires sphingosine 1-phosphate (S1P)-mediated translocation of the protease to cell-cell junctions in human mammary epithelial cells. In the present study, we further explored how HAI-1 regulates this protease. First, we observed that after S1P treatment HAI-1 was cotranslocated with matriptase to cell-cell junctions and that the cellular ratio of HAI-1 to matriptase was maintained during this process. However, when this ratio was changed by cell treatment with HAI-1 small interfering RNA or anti-HAI-1 MAb M19, spontaneous activation of matriptase occurred in the absence of S1P-induced translocation; S1P-induced matriptase activation was also enhanced. These results support a role for HAI-1 in protection of cell from uncontrolled matriptase activation. We next expressed matriptase, either alone or with HAI-1 in breast cancer cells that do not endogenously express either protein. A defect in matriptase trafficking to the cell surface occurred if wild-type matriptase was expressed in the absence of HAI-1; this defect appeared to result from matriptase toxicity to cells. Coexpression with matriptase of wild-type HAI-1, but not HAI-1 mutants altered in its Kunitz domain 1, corrected the trafficking defect. In contrast, catalytically defective matriptase mutants were normal in their trafficking in the absence of HAI-1. These results are also consistent with a role for HAI-1 to prevent inappropriate matriptase proteolytic activity during its protein synthesis and trafficking. Taken together, these results support multiple roles for HAI-1 to regulate matriptase, including its proper expression, intracellular trafficking, activation, and inhibition.
authors.affiliation: Department of Oncology, Lombardi Cancer Center, Georgetown University Medical Center, 3970 Reservoir Rd. NW, Washington, DC 20007, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Oberst
authors.forename: Li-Yuan L
authors.initials: LY
authors.lastname: Chen
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Kiyomiya
authors.forename: Cicely A
authors.initials: CA
authors.lastname: Williams
authors.forename: Ming-Shyue
authors.initials: MS
authors.lastname: Lee
authors.forename: Michael D
authors.initials: MD
authors.lastname: Johnson
authors.forename: Robert B
authors.initials: RB
authors.lastname: Dickson
authors.forename: Chen-Yong
authors.initials: CY
authors.lastname: Lin
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D004789:Enzyme Activation / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D008246:Lysophospholipids / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D021381:Protein Transport / Q000502:physiology*; D053491:Proteinase Inhibitory Proteins, Secretory; D034741:RNA, Small Interfering; D012697:Serine Endopeptidases / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D014162:Transfection
chemical_list: D008246:Lysophospholipids; D008562:Membrane Glycoproteins; D053491:Proteinase Inhibitory Proteins, Secretory; D034741:RNA, Small Interfering; C109149:SPINT1 protein, human; C060506:sphingosine 1-phosphate; D012697:Serine Endopeptidases; C485595:matriptase; D013110:Sphingosine