Suspension of cultured human foreskin keratinocytes (HKs) with trypsin phosphorylates tyrosine residues on an 80-kDa membrane glycoprotein, p80 (Xia, Y., Gil, S. G., and Carter, W. G. (1996) J. Cell Biol. 132, 727-740). Readhesion dephosphorylates p80. Sequencing of a p80 cDNA established identity to CUB domain-containing protein 1 (CDCP1), a gene elevated in carcinomas. CDCP1/p80 cDNA encodes three extracellular CUB domains, a transmembrane domain, and two putative cytoplasmic Tyr phosphorylation sites. Treatment of adherent HKs with suramin, a heparin analogue, or inhibitors of phosphotyrosine phosphatases (PTPs; vanadate or calpeptin) increases phosphorylation of p80 and a novel 140-kDa membrane glycoprotein, gp140. Phosphorylated gp140 was identified as a trypsin-sensitive precursor to p80. Identity was confirmed by digestion and phosphorylation studies with recombinant gp140-GFP. Plasmin, a serum protease, also converts gp140 to p80, providing biological significance to the cleavage in wounds. Phosphorylation of gp140 and p80 are mediated by Src family kinases at multiple Tyr residues including Tyr 734 . Dephosphorylation is mediated by PTP(s). Conversion of gp140 to p80 prolongs phosphorylation of p80 in response to suramin and changes in adhesion. This distinguishes gp140 and p80 and explains the relative abundance of phosphorylated p80 in trypsinized HKs. We conclude that phosphorylation of gp140 is dynamic and balanced by Src family kinase and PTPs yielding low equilibrium phosphorylation. We suggest that the balance is altered by conversion of gp140 to p80 and by adhesion, providing a novel transmembrane phosphorylation signal in epithelial wounds.Wounding of quiescent epidermis activates changes in adhesion and cell signaling resulting in keratinocyte migration, basement membrane (BM) 1 repair, and wound closure (1-3).Based on an in vitro model for wound activation, we reported that trypsin detachment of cultured human foreskin keratinocytes (HKs) promotes phosphorylation of tyrosine residues on an 80-kDa membrane glycoprotein (p80) (4). Phosphorylated p80 (P-p80) in suspended HKs is dephosphorylated upon readhesion to laminin 5 via integrins ␣ 6 ␤ 4 and ␣ 3 ␤ 1 . In work here, we purified and characterized p80. We wished to understand whether phosphorylated p80 identified in an in vitro deadhesion/readhesion screen (4) might be involved in physiologically significant wound activation. Quiescent epidermis adheres to laminin 5 in the BM via integrin ␣ 6 ␤ 4 in hemidesmosome (HD) cell junctions. Wounding epidermis generates leading and following subpopulations of keratinocytes at the wound margin (5). Leading keratinocytes migrate over exposed dermal collagen via integrin ␣ 2 ␤ 1 and fibronectin via integrin ␣ 5 ␤ 1 . However, leading cells also deposit laminin 5 as a provisional BM and interact with these deposits via integrin ␣ 3 ␤ 1 (5-7). The interaction of leading cells with deposited laminin 5 generates distinct transmembrane signals when compared with interaction with dermal ligands. For example,...

In epidermal wounds, precursor laminin 5 (α3β3γ2) is deposited in the provisional basement membrane (PBM) before other BM components. Precursor laminin 5 contains G4/5 globular domains at the carboxyl terminus of the α3 chain. Here, the function of G4/5 was evaluated in deposition of laminin 5. Soluble laminin 5, secreted by keratinocytes in culture, is cleaved by an endogenous protease releasing G4/5. Thrombin, a serum protease, cleaves G4/5 indistinguishably from endogenous protease. Soluble human precursor laminin 5, but not cleaved laminin 5, was bound and deposited by mouse keratinocytes null for mouse α3 chain (α3–/– MKs). The deposition rescued adhesion and spreading and survival. In a model for PBM assembly, precursor laminin 5 was deposited along fibronectin fibrils at the junction between co-cultures of keratinocytes and fibroblasts. In both models, the deposition of precursor laminin 5 was inhibited by removal of G4/5 with thrombin. To confirm that G4/5 participates in deposition, the human LAMA3A gene was modified to produce α3 chains either without or with G4/5 that cannot be cleaved. Both precleaved and noncleavable α3 isoforms were expressed in α3–/– MKs, where they deposited sufficiently to rescue adhesion via integrins α3β1 and α6β4. Despite this similarity, noncleavable laminin 5 was at least threefold more efficiently deposited than precleaved isoform. We conclude that the G4/5 domain in the α3 chain facilitates deposition of precursor laminin 5 into the PBM in epidermal wounds.

Little is known about the fate of normal human mammary epithelial cells (HMECs) that lose p53 function in the context of extracellular matrix (ECM)–derived growth and polarity signals. Retrovirally mediated expression of human papillomavirus type 16 (HPV-16) E6 and antisense oligodeoxynucleotides (ODNs) were used to suppress p53 function in HMECs as a model of early breast cancer. p53+ HMEC vector controls grew exponentially in reconstituted ECM (rECM) until day 6 and then underwent growth arrest on day 7. Ultrastructural examination of day 7 vector controls revealed acinus-like structures characteristic of normal mammary epithelium. In contrast, early passage p53− HMEC cells proliferated in rECM until day 6 but then underwent apoptosis on day 7. p53− HMEC-E6 passaged in non-rECM culture rapidly (8–10 passages), lost sensitivity to both rECM-induced growth arrest and polarity, and also developed resistance to rECM-induced apoptosis. Resistance was associated with altered expression of α3-integrin. Treatment of early passage p53− HMEC-E6 cells with either α3- or β1-integrin function-blocking antibodies inhibited rECM-mediated growth arrest and induction of apoptosis. Our results indicate that suppression of p53 expression in HMECs by HPV-16 E6 and ODNs may sensitize cells to rECM-induced apoptosis and suggest a role for the α3/β1-heterodimer in mediating apoptosis in HMECs grown in contact with rECM.

No abstract

No abstract