Aberrant splicing of the E-cadherin transcript is a novel mechanism of gene silencing in chronic lymphocytic leukemia cells.
Premature termination codon (PTC) mutations are due to insertion or deletion of nucleotides causing a frameshift and premature termination codon in RNA. These transcripts are degraded by the nonsense-mediated decay pathway and have a very short half-life. We used a microarray technique to screen for genes that up-regulate their RNA signal upon nonsense-mediated decay pathway blockade in chronic lymphocytic leukemia (CLL) specimens and identified an E-cadherin transcript with PTC. Sequencing revealed an aberrant E-cadherin transcript lacking exon 11, resulting in a frameshift and PTC. The aberrant E-cadherin transcript was also identified in normal B cells, but occurred at a much lower level compared with CLL cells. In CLL specimens, E-cadherin expression was depressed more than 50% in 62% cases (relative to normal B cells). By real-time polymerase chain reaction analysis, the relative amounts of wild-type transcript inversely correlated with amounts of aberrant transcript (P = .018). Ectopic expression of E-cadherin in CLL specimens containing high amounts of aberrant transcript resulted in down-regulation of the wnt-beta-catenin pathway reporter, a pathway known to be up-regulated in CLL. Our data point to a novel mechanism of E-cadherin gene inactivation, with CLL cells displaying a higher proportion of aberrant nonfunctional transcripts and resulting up-regulation of the wnt-beta-catenin pathway.
Sharma
Sanjai
S
Division of Hematology Oncology, University of California-West Los Angeles Veterans Administration Medical Center, Los Angeles, CA 90073, USA. sasharma@mednet.ucla.edu
Lichtenstein
Alan
A
D017398:Alternative Splicing / Q000187:drug effects; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D001483:Base Sequence; D015820:Cadherins / Q000235:genetics*; D018389:Codon, Nonsense; D017931:DNA Primers / Q000235:genetics; D004640:Emetine / Q000494:pharmacology; D016368:Frameshift Mutation; D020868:Gene Silencing; D006801:Humans; D066298:In Vitro Techniques; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D020365:RNA Helicases; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
C495270:CTNNB1 protein, human; D015820:Cadherins; D018389:Codon, Nonsense; D017931:DNA Primers; D012334:RNA, Neoplasm; D034741:RNA, Small Interfering; D015534:Trans-Activators; D051153:Wnt Proteins; D051176:beta Catenin; D020365:RNA Helicases; C101828:UPF1 protein, human; D004640:Emetine