Overexpression of alpha1beta1 integrin directly affects rat mesangial cell behavior.
BACKGROUND
Glomerular mesangial cell (MC) proliferation, hypertrophy, and abnormal matrix remodeling characterized by increased expression of fibronectin, laminin and collagen type IV, and neoexpression of collagen I and III are the main biological features of progressive glomerulonephritis (GN). Especially, persistent pathological matrix remodeling may lead to glomerular scar formation (glomerular scarring). We reported recently that alpha1beta1 integrin, a major collagen receptor for MCs, may be a potential adhesion molecule for MC-mediated pathological collagen matrix remodeling in GN.


METHODS
To address further the direct role of alpha1beta1 integrin in MC behavior, such as cell growth and matrix remodeling, alpha1beta1 integrin was overexpressed in MCs by transfecting an expression vector containing a full-length rat alpha1 integrin cDNA. Flow cytometry and immunoprecipitation analysis were applied for selection of transfectants with a stable expression of the alpha1 integrin subunit. The effect of alpha1beta1 integrin overexpression on MC biology was examined with a 3H-thymidine incorporation assay, flow cytometric analysis of cell size and DNA content, Western blot analysis of a cyclin-dependent-kinase inhibitor, p27Kip1, alpha-smooth muscle actin expression, and a collagen gel contraction assay.


RESULTS
The alpha1 transfectants displayed a dramatic inhibition of 3H-thymidine incorporation as compared with the mock transfectants. Increased expression of the alpha1 subunit inversely correlated with cell cycle progression and paralleled the expression of p27Kip1 and alpha-smooth muscle actin, as well as the cell size in MCs. In addition, the alpha1-transfectants were able to enhance collagen matrix reorganization effectively.


CONCLUSIONS
These results indicate that MC-alpha1beta1 integrin expression is a critical determinant of MC phenotypes, including cell growth, cell size, and collagen matrix remodeling ability, and thereby contributes to scar matrix remodeling (sclerosis) in GN.
Kagami
S
S
Department of Pediatrics, School of Medicine, University of Tokushima, Tokushima, Japan, and Institute für Molekularbiologie und Biochemi, Freie Universitat Berlin, Berlin-Dahlem, Germany. kagami@medclin.clin.med.tokushima-u.ac.jp
Kondo
S
S
Urushihara
M
M
Löster
K
K
Reutter
W
W
Saijo
T
T
Kitamura
A
A
Kobayashi
S
S
Kuroda
Y
Y
D000199:Actins / Q000235:genetics; D000818:Animals; D019556:COS Cells; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000502:physiology; D002921:Cicatrix / Q000473:pathology / Q000503:physiopathology; D003001:Cloning, Molecular; D003094:Collagen / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D005109:Extracellular Matrix / Q000378:metabolism; D005434:Flow Cytometry; D015870:Gene Expression / Q000502:physiology; D005920:Glomerular Mesangium / Q000473:pathology* / Q000502:physiology*; D005923:Glomerulosclerosis, Focal Segmental / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D006984:Hypertrophy; D039222:Integrin alpha1beta1; D016023:Integrins / Q000235:genetics*; D008869:Microtubule-Associated Proteins / Q000235:genetics; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D014162:Transfection; D025521:Tumor Suppressor Proteins
D000199:Actins; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D039222:Integrin alpha1beta1; D016023:Integrins; D008869:Microtubule-Associated Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003094:Collagen