title: Metastasis of tumor cells is enhanced by downregulation of Bit1.
abstract: BACKGROUND
  Resistance to anoikis, which is defined as apoptosis induced by loss of integrin-mediated cell attachment to the extracellular matrix, is a determinant of tumor progression and metastasis. We have previously identified the mitochondrial Bit1 (Bcl-2 inhibitor of transcription) protein as a novel anoikis effector whose apoptotic function is independent from caspases and is uniquely controlled by integrins. In this report, we examined the possibility that Bit1 is suppressed during tumor progression and that Bit1 downregulation may play a role in tumor metastasis.
  
  
  RESULTS
  Using a human breast tumor tissue array, we found that Bit1 expression is suppressed in a significant fraction of advanced stages of breast cancer. Targeted disruption of Bit1 via shRNA technology in lowly aggressive MCF7 cells conferred enhanced anoikis resistance, adhesive and migratory potential, which correlated with an increase in active Extracellular kinase regulated (Erk) levels and a decrease in Erk-directed phosphatase activity. These pro-metastasis phenotypes were also observed following downregulation of endogenous Bit1 in Hela and B16F1 cancer cell lines. The enhanced migratory and adhesive potential of Bit1 knockdown cells is in part dependent on their high level of Erk activation since down-regulating Erk in these cells attenuated their enhanced motility and adhesive properties. The Bit1 knockdown pools also showed a statistically highly significant increase in experimental lung metastasis, with no differences in tumor growth relative to control clones in vivo using a BALB/c nude mouse model system. Importantly, the pulmonary metastases of Bit1 knockdown cells exhibited increased phospho-Erk staining.
  
  
  CONCLUSIONS
  These findings indicate that downregulation of Bit1 conferred cancer cells with enhanced anoikis resistance, adhesive and migratory properties in vitro and specifically potentiated tumor metastasis in vivo. These results underscore the therapeutic importance of restoring Bit1 expression in cancer cells to circumvent metastasis at least in part through inhibition of the Erk pathway.
authors: Sanford-Burnham Medical Research Institute, La Jolla, California, United States of America.
authors: Priya Prakash
authors: PP
authors: Karmali
authors: Chris
authors: C
authors: Brunquell
authors: Hau
authors: H
authors: Tram
authors: Shubha Kale
authors: SK
authors: Ireland
authors: Erkki
authors: E
authors: Ruoslahti
authors: Hector
authors: H
authors: Biliran
mesh_terms: D000818:Animals; D023102:Anoikis; D001943:Breast Neoplasms / Q000473:pathology*; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D018450:Disease Progression; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000556:secondary*; D020935:MAP Kinase Signaling System; D051379:Mice; D008807:Mice, Inbred BALB C; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000473:pathology
chemical_list: D002265:Carboxylic Ester Hydrolases; C527112:Ptrh2 protein, mouse