title: Alternative splice variants of AID are not stoichiometrically present at the protein level in chronic lymphocytic leukemia.
abstract: Activation-induced deaminase (AID) is a DNA-mutating enzyme that mediates class-switch recombination as well as somatic hypermutation of antibody genes in B cells. Due to off-target activity, AID is implicated in lymphoma development by introducing genome-wide DNA damage and initiating chromosomal translocations such as c-myc/IgH. Several alternative splice transcripts of AID have been reported in activated B cells as well as malignant B cells such as chronic lymphocytic leukemia (CLL). As most commercially available antibodies fail to recognize alternative splice variants, their abundance in vivo, and hence their biological significance, has not been determined. In this study, we assessed the protein levels of AID splice isoforms by introducing an AID splice reporter construct into cell lines and primary CLL cells from patients as well as from WT and TCL1(tg) C57BL/6 mice (where TCL1 is T-cell leukemia/lymphoma 1). The splice construct is 5'-fused to a GFP-tag, which is preserved in all splice isoforms and allows detection of translated protein. Summarizing, we show a thorough quantification of alternatively spliced AID transcripts and demonstrate that the corresponding protein abundances, especially those of splice variants AID-ivs3 and AID-ΔE4, are not stoichiometrically equivalent. Our data suggest that enhanced proteasomal degradation of low-abundance proteins might be causative for this discrepancy.
authors.affiliation: Laboratory for Immunological and Molecular Cancer Research, Department of Internal Medicine III with Hematology, Medical Oncology, Hemostaseology, Infectious Diseases, Rheumatology, Oncologic Center, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rebhandl
authors.forename: Michael
authors.initials: M
authors.lastname: Huemer
authors.forename: Nadja
authors.initials: N
authors.lastname: Zaborsky
authors.forename: Franz Josef
authors.initials: FJ
authors.lastname: Gassner
authors.forename: Kemal
authors.initials: K
authors.lastname: Catakovic
authors.forename: Thomas Klaus
authors.initials: TK
authors.lastname: Felder
authors.forename: Richard
authors.initials: R
authors.lastname: Greil
authors.forename: Roland
authors.initials: R
authors.lastname: Geisberger
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D003564:Cytidine Deaminase / Q000032:analysis / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology*; D008810:Mice, Inbred C57BL; D060888:Real-Time Polymerase Chain Reaction; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase
keywords: Activation-induced deaminase (AID); Alternative splicing; Chronic lymphocytic leukemia (CLL)