title: Integrin subunits alpha5 and alpha6 regulate cell cycle by modulating the chk1 and Rb/E2F pathways to affect breast cancer metastasis.
abstract: BACKGROUND
  Although integrins have been implicated in the progression of breast cancer, the exact mechanism whereby they exert this regulation is clearly not understood. To understand the role of integrins in breast cancer, we examined the expression levels of several integrins in mouse breast cancer cell lines by flow cytometry and the data were validated by Western and RT-PCR analysis. The importance of integrins in cell migration and cell invasion was examined by in vitro assays. Further the effect of integrins on metastasis was investigated by in vivo experimental metastasis assays using mouse models.
  
  
  RESULTS
  Integrin α5 subunit is highly expressed in the nonmetastatic cell line 67NR and is significantly low in the highly invasive cell line 4T1. In contrast, expression levels of integrin α6 subunit are high in 4T1 cells and low in 67NR cells. In vitro data indicated that overexpression of α5 subunit and knockdown of α6 integrin subunit inhibited cell proliferation, migration, and invasion. Our in vivo findings indicated that overexpression of integrin α5 subunit and knockdown of α6 subunit decreased the pulmonary metastasis property of 4T1 cells. Our data also indicated that overexpression of alpha 5 integrin subunit and suppression of alpha6 integrin subunit inhibited cells entering into S phase by up-regulating p27, which results in downregulation of cyclinE/CDK2 complexes, This suggests that these integrins regulate cell growth through their effects on cell-cycle-regulated proteins. We also found that modulation of these integrins upregulates E2F, which may induce the expression of chk1 to regulate cdc25A/cyclin E/CDK2/Rb in a feedback loop mechanism.
  
  
  CONCLUSIONS
  This study indicates that Integrin α5 subunit functions as a potential metastasis suppressor, while α6 subunit functions as a metastasis promoter. The modulation of integrins reduces cdc25 A, another possible mechanism for downregulation of CDK2. Taken together we demonstrate a link between integrins and the chk1-cdc25-cyclin E/CDK2-Rb pathway.
authors.affiliation: Department of Biochemistry and Molecular Biology, Stanley Scott Cancer Center, LSU Health Sciences Center, New Orleans, LA 70112, USA.
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Wang
authors.forename: Sylvia
authors.initials: S
authors.lastname: Shenouda
authors.forename: Somesh
authors.initials: S
authors.lastname: Baranwal
authors.forename: Rajamani
authors.initials: R
authors.lastname: Rathinam
authors.forename: Prachi
authors.initials: P
authors.lastname: Jain
authors.forename: Lili
authors.initials: L
authors.lastname: Bao
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Hazari
authors.forename: Srikanta
authors.initials: S
authors.lastname: Dash
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Alahari
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002277:Carcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002453:Cell Cycle / Q000235:genetics* / Q000502:physiology; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D050684:E2F Transcription Factors / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D039482:Integrin alpha5 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D039503:Integrin alpha6 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008819:Mice, Nude; D009362:Neoplasm Metastasis; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D021122:Protein Subunits / Q000502:physiology; D016160:Retinoblastoma Protein / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D050684:E2F Transcription Factors; D039482:Integrin alpha5; D039503:Integrin alpha6; D021122:Protein Subunits; D016160:Retinoblastoma Protein; D011494:Protein Kinases; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse