Restricted expression and function of laminin 1-binding integrins in normal and malignant oral mucosal keratinocytes.
Squamous cell carcinoma of the oral cavity spreads by initial invasion of the laminin-rich basement membrane. We examined the adhesion and motility of human oral SCC cells and normal mucosal keratinocytes and found that the SCC cells readily attached and migrated on laminin 1 substrates but migrated poorly on collagen type I and fibronectin. The normal keratinocytes, however, adhered poorly to and were non-motile on laminin 1 yet readily and preferentially attached and migrated on fibronectin and collagen type I. Analysis with blocking anti-integrin antibodies showed that the SCC cells used the alpha 6 beta 1 complex to attach and migrate on laminin 1 and that this activity was confined to the E8 long arm fragment of laminin. Affinity chromatography on laminin-Sepharose columns revealed that the SCC cells, but not normal keratinocytes, expressed high levels of the alpha 6 beta 1 laminin 1 receptor. Metabolic pulse-chase analysis indicated that in contrast to the SCC cells, keratinocytes did not have a stable pool of beta 1 subunit precursor. Preferential pairing of alpha 6 with beta 4 and the deficiency in pre-beta 1 levels appear to account for the failure of keratinocytes to form significant alpha 6 beta 1 complex. Additionally, the presence of laminin 1 in co-coating experiments blocked keratinocyte adhesion to other immobilized ligands, such as collagen type I or fibronectin. This anti-adhesive effect seemed to reflect a general paralysis of cell adhesive function, since laminin 1 also diminished the adhesion of keratinocytes to substrates coated with immobilized anti-integrin subunit antibody. The inhibitory activity of laminin 1 resided in the E1' and E8 fragments, and not in the E3, E4 or G domains. Collectively, our results indicate that laminin 1 is a restrictive ligand for normal keratinocytes, apparently because of their failure to assemble and express the alpha 6 beta 1 complex or other functional laminin receptors and their sensitivity to the anti-adhesive activity of laminin itself. The elevated expression of alpha 6 beta 1 following malignant conversion of muscosal keratinocytes promotes their migration on laminin, a process important during invasion and metastasis.
Zhang
K
K
Department of Anatomy, University of California, San Francisco 94143, USA.
Kim
J P
JP
Woodley
D T
DT
Waleh
N S
NS
Chen
Y Q
YQ
Kramer
R H
RH
D001667:Binding, Competitive; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002465:Cell Movement; D002478:Cells, Cultured; D005353:Fibronectins / Q000378:metabolism; D015870:Gene Expression; D005881:Gingiva / Q000166:cytology*; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology*; D007797:Laminin / Q000378:metabolism*; D008024:Ligands; D009062:Mouth Neoplasms / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics
D015815:Cell Adhesion Molecules; D005353:Fibronectins; D016023:Integrins; D007797:Laminin; D008024:Ligands; D012333:RNA, Messenger