HEMCAM/CD146 downregulates cell surface expression of beta1 integrins.
HEMCAM/gicerin, an immunoglobulin superfamily protein, is involved in homophilic and heterophilic adhesion. It interacts with NOF (neurite outgrowth factor), a molecule of the laminin family. Alternative splicing leads to mRNAs coding for HEMCAM with a short (HEMCAM-s) or a long cytoplasmic tail (HEMCAM-l). To investigate the cellular function of these two variants, we stably transfected murine fibroblasts with either form of HEMCAM. Expression of each isoform of this protein in L cells delayed proliferation and modified their adhesion properties to purified extracellular matrix proteins. Expression of either HEMCAM-s or HEMCAM-l inhibited integrin-dependent adhesion and spreading of fibroblasts to laminin 1, showing that this phenomenon did not depend on the cytoplasmic region. By contrast, L-cell adhesion and spreading to fibronectin depended on the HEMCAM isoform expressed. Flow cytometry and immunoprecipitation studies revealed that the expression of HEMCAM downregulated expression of the laminin-binding integrins alpha3beta1, alpha6beta1 and alpha7beta1, and fibronectin receptor alpha5beta1 from the cell surface. Semi-quantitative PCR and northern blot experiments showed that the expression of alpha6beta1 integrin modified by HEMCAM occurred at a translation or maturation level. Thus, our data demonstrate that HEMCAM regulates fibroblast adhesion by controlling beta1 integrin expression.
Alais
S
S
UMR-CNRS 7622, Université Pierre et Marie Curie, Paris, France.
Allioli
N
N
Pujades
C
C
Duband
J L
JL
Vainio
O
O
Imhof
B A
BA
Dunon
D
D
D000818:Animals; D015703:Antigens, CD; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism; D030161:Avian Proteins; D051929:CD146 Antigen; D002448:Cell Adhesion / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000235:genetics* / Q000378:metabolism*; D002455:Cell Division / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D002642:Chick Embryo; D015536:Down-Regulation / Q000502:physiology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005434:Flow Cytometry; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D039121:Integrin alpha6beta1; D019012:Integrin beta1 / Q000235:genetics* / Q000378:metabolism*; D016023:Integrins / Q000235:genetics / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D019006:Neural Cell Adhesion Molecules; D012333:RNA, Messenger / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection
D015703:Antigens, CD; D000954:Antigens, Surface; D030161:Avian Proteins; D051929:CD146 Antigen; D015815:Cell Adhesion Molecules; D039121:Integrin alpha6beta1; D019012:Integrin beta1; D016023:Integrins; C497902:MCAM protein, human; C497903:Mcam protein, mouse; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D019006:Neural Cell Adhesion Molecules; D012333:RNA, Messenger; C086935:gicerin protein, Gallus gallus