title: Leucine-rich repeats of the class II transactivator control its rate of nuclear accumulation.
abstract: Activation of class II major histocompatibility complex (MHC) gene expression is regulated by a master regulator, class II transcriptional activator (CIITA). Transactivation by CIITA requires its nuclear import. This study will address a mechanistic role for the leucine-rich repeats (LRR) of CIITA in regulating nuclear translocation by mutating 12 individual consensus-motif "leucine" residues in both its alpha-motifs and beta-motifs. While some leucine mutations in the LRR motif of CIITA cause congruent loss of transactivation function and nuclear import, other alanine substitutions in both the alpha-helices and the beta-sheets have normal transactivation function but a loss of nuclear accumulation (i.e., functional mutants). This seeming paradox is resolved by the observations that nuclear accumulation of these functional mutants does occur but is significantly less than wild-type. This difference is revealed only in the presence of leptomycin B and actinomycin D, which permit examination of nuclear accumulation unencumbered by nuclear export and new CIITA synthesis. Further analysis of these mutants reveals that at limiting concentrations of CIITA, a dramatic difference in transactivation function between mutants and wild-type CIITA is easily detected, in agreement with their lowered nuclear accumulation. These experiments reveal an interesting aspect of LRR in controlling the amount of nuclear accumulation.
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Harton
authors.forename: William
authors.initials: W
authors.lastname: O'Connor
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Conti
authors.forename: Michael W
authors.initials: MW
authors.lastname: Linhoff
authors.forename: Jenny P-Y
authors.initials: JP
authors.lastname: Ting
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007930:Leucine / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000949:Histocompatibility Antigens Class II; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D007930:Leucine