title: LIP expression is regulated by IGF-1R signaling and participates in suppression of anoikis.
abstract: BACKGROUND
  The transcription factor, CCAAT enhancer binding protein-β (C/EBPβ), is expressed as several distinct protein isoforms (LAP1, LAP2 and LIP) that have opposing actions in cellular proliferation and differentiation. Increases in the ratio of LIP/LAP are associated with aggressive, metastatic breast cancer; however, little is known regarding the molecular mechanisms that regulate LIP expression or the biological actions of an increase in the LIP/LAP ratio. Metastasis is highly dependent upon the suppression of anoikis and the role of C/EBPβ and LIP in this anchorage-independent, survival process is currently not known in mammary epithelial cells. IGF-1R signaling is important for the survival of breast cancer cells and crosstalk between IGF-1R and EGFR signaling pathways have been implicated in the development of more aggressive disease. We therefore evaluated in mammary epithelial cells whether IGF-1R signaling regulates the LIP/LAP ratio, analyzed the potential interplay between EGFR and IGF-1R signaling and addressed the biological significance of increased LIP expression in cellular survival and suppression of anoikis.
  
  
  RESULTS
  Our data provide the first evidence that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. Although crosstalk between IGF-1R signaling and EGFR signaling is detectable in MCF10A cells, this crosstalk is not required for the IGF-1 mediated regulation of LIP expression. Rather, the critical regulator of IGF-1 induced LIP expression appears to be EGFR-independent, Akt activity. Our data also demonstrate that increases in LIP expression promote cell survival via suppression of anoikis. Likewise, knockdown of total C/EBPβ leads to increased cell death and suggest that C/EBPβ expression is important for survival and resistance to anoikis. IGF-1 treatment can partially rescue vector control cells from anoikis; however, cells with reduced C/EBPβ expression do not survive anoikis.
  
  
  CONCLUSIONS
  Taken together, our data demonstrate that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. C/EBPβ expression and elevations in LIP play an important role in regulating cellular survival via suppression of anoikis, in an IGF-1R mediated context or in a manner independent of IGF-1R signaling.
authors.affiliation: Department of Oncology, the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland 21231, USA.
authors.forename: Huili
authors.initials: H
authors.lastname: Li
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Baldwin
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Zahnow
mesh_terms: D023102:Anoikis; D001943:Breast Neoplasms; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D017930:Genes, Reporter; D006801:Humans; D049410:Luciferases, Renilla / Q000096:biosynthesis / Q000235:genetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000494:pharmacology / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D066246:ErbB Receptors; D049410:Luciferases, Renilla; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D017526:Receptor, IGF Type 1; C508053:ERBB2 protein, human