title: Mechanisms of confluence-dependent expression of CD26 in colon cancer cell lines.
abstract: BACKGROUND
  CD26 (dipeptidyl peptidase IV, DPPIV) is a 110 kDa surface glycoprotein expressed in most normal tissues, and is a potential novel therapeutic target for selected cancers. Our work evaluates the mechanism involved in confluence-dependent CD26 expression in colon cancer.
  
  
  METHODS
  Colon adenocarcinoma cells were grown to confluence, and expression of CD26 and transcription factors implicated in its regulation was confirmed by immunofluorescence and Western blotting. Real-time PCR was also performed to evaluate CD26 upregulation at the transcriptional level. The influence of c-Myc on CD26 expression during different growth conditions was further evaluated following transient transfection of a c-Myc-expressing plasmid and a c-Myc specific siRNA.
  
  
  RESULTS
  We found that the colon cancer cell lines HCT-116 and HCT-15 exhibited a confluence-dependent increase in CD26 mRNA and protein, associated with decreased expression of c-Myc, increased USF-1 and Cdx 2 levels, and unchanged HNF-1α expression. Meanwhile, ectopic expression of c-Myc in both cell lines led to decreased CD26 expression. In contrast, transfection of a siRNA targeted to Cdx2 resulted in decreased CD26 level. Importantly, culturing of cells in serum-depleted media, but not acidic conditions, upregulated CD26. While HIF-1α level also increased when cells were cultured in serum-depleted media, its expression was required but not sufficient for CD26 upregulation.
  
  
  CONCLUSIONS
  CD26 mRNA and protein levels increase in a confluence-dependent manner in colon carcinoma cell lines, with c-Myc acting as a repressor and Cdx2 acting as an enhancer of CD26 expression. The enhanced expression of CD26 in serum-depleted media and a requirement for HIF-1α suggest a role for nutrients or growth factors in the regulation of CD26 protein expression.
authors.affiliation: Department of Hematologic Malignancies, Nevada Cancer Institute, Las Vegas, Nevada, 89135, USA.
authors.forename: Masako
authors.initials: M
authors.lastname: Abe
authors.forename: Pamela A
authors.initials: PA
authors.lastname: Havre
authors.forename: Yasuyo
authors.initials: Y
authors.lastname: Urasaki
authors.forename: Kei
authors.initials: K
authors.lastname: Ohnuma
authors.forename: Chikao
authors.initials: C
authors.lastname: Morimoto
authors.forename: Long H
authors.initials: LH
authors.lastname: Dang
authors.forename: Nam H
authors.initials: NH
authors.lastname: Dang
mesh_terms: D015153:Blotting, Western; D000071616:CDX2 Transcription Factor; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002465:Cell Movement; D049109:Cell Proliferation; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018819:Dipeptidyl Peptidase 4 / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D045325:HCT116 Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D000071616:CDX2 Transcription Factor; D018398:Homeodomain Proteins; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D015534:Trans-Activators; C042807:DPP4 protein, human; D018819:Dipeptidyl Peptidase 4