A novel alternative splicing isoform of human T-cell leukemia virus type 1 bZIP factor (HBZ-SI) targets distinct subnuclear localization.
Adult T-cell leukemia (ATL) is associated with prior infection with human T-cell leukemia virus type 1 (HTLV-1); however, the mechanism by which HTLV-1 causes adult T-cell leukemia has not been fully elucidated. Recently, a functional basic leucine zipper (bZIP) protein coded in the minus strand of HTLV-1 genome (HBZ) was identified. We report here a novel isoform of the HTLV-1 bZIP factor (HBZ), HBZ-SI, identified by means of reverse transcription-PCR (RT-PCR) in conjunction with 5' and 3' rapid amplification of cDNA ends (RACE). HBZ-SI is a 206-amino-acid-long protein and is generated by alternative splicing between part of the HBZ gene and a novel exon located in the 3' long terminal repeat of the HTLV-1 genome. Consequently, these isoforms share >95% amino acid sequence identity, and differ only at their N termini, indicating that HBZ-SI is also a functional protein. Duplex RT-PCR and real-time quantitative RT-PCR analyses showed that the mRNAs of these isoforms were expressed at equivalent levels in all ATL cell samples examined. Nonetheless, we found by Western blotting that the HBZ-SI protein was preferentially expressed in some ATL cell lines examined. A key finding was obtained from the subcellular localization analyses of these isoforms. Despite their high sequence similarity, each isoform was targeted to distinguishable subnuclear structures. These data show the presence of a novel isoform of HBZ in ATL cells, and in addition, shed new light on the possibility that each isoform may play a unique role in distinct regions in the cell nucleus.
Murata
Ken
K
Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, Japan. kmurata@grape.med.tottori-u.ac.jp
Hayashibara
Toshihisa
T
Sugahara
Kazuyuki
K
Uemura
Akiko
A
Yamaguchi
Taku
T
Harasawa
Hitomi
H
Hasegawa
Hiroo
H
Tsuruda
Kazuto
K
Okazaki
Toshiro
T
Koji
Takehiko
T
Miyanishi
Takayuki
T
Yamada
Yasuaki
Y
Kamihira
Shimeru
S
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D019677:Artificial Gene Fusion; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism*; D012191:Retroviridae Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
D050976:Basic-Leucine Zipper Transcription Factors; C479751:HBZ protein, human T-cell leukemia virus type I; D020033:Protein Isoforms; D012333:RNA, Messenger; D012367:RNA, Viral; D012191:Retroviridae Proteins; D014764:Viral Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins