Release from quiescence stimulates the expression of integrin alpha 5 beta 1 which regulates DNA synthesis in human fibrosarcoma HT1080 cells.
We show that integrin alpha 5 subunit expression is stimulated when human fibrosarcoma HT1080 cells are released from quiescence. The alpha 5 subunit mRNA level in quiescent HT1080 cells was increased 24 hr after their release by 10% fetal bovine serum-containing medium reaching a maximum of 2.5 fold on day 2. Similar levels of induction of cell-surface alpha 5 subunit protein as well as beta 1 subunit protein were also observed. This resulted in a significant increase of cell attachment to fibronectin. The serum stimulation also increased alpha 5 subunit promoter activity by twofold which was protein synthesis independent. Subsequent deletion of alpha 5 subunit promoter DNA showed that the cis-element responsible for the activation is located between -92 bp and the transcription start site. The promoter activity was not induced until 12 hr after the release. Comparison of the effect of a serum-free medium and a 10% fetal bovine serum-supplemented medium revealed that both the DNA synthesis and alpha 5 subunit induction were independent of exogenous growth factors. The increased integrin alpha 5 beta 1 appears to function by reducing mitogenic activity since blockade of fibronectin binding to its receptor with a RGD peptide, a monoclonal anti-fibronectin antibody, or a monoclonal anti-alpha 5 subunit antibody during the release from quiescence significantly stimulated DNA synthesis. On the other hand, stable overexpression of the alpha 5 subunit resulted in decreased DNA synthesis.
Wang
D
D
Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo 43699-0008, USA.
Birkenmeier
T M
TM
Yang
J
J
Venkateswarlu
S
S
Humphrey
L
L
Brattain
M G
MG
Sun
L
L
D002448:Cell Adhesion; D002453:Cell Cycle; D004273:DNA, Neoplasm / Q000096:biosynthesis; D005353:Fibronectins / Q000502:physiology; D005354:Fibrosarcoma / Q000235:genetics / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D066298:In Vitro Techniques; D016023:Integrins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D017469:Receptors, Fibronectin / Q000235:genetics*; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D005353:Fibronectins; D016023:Integrins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D017469:Receptors, Fibronectin