A novel autoregulatory mechanism for transcriptional activation of the IL-15 gene by a nonsecretable isoform of IL-15 generated by alternative splicing.
There are several isoforms of interleukin (IL) -15 generated by alternating splicing. We reported previously that alternative IL-15 transgenic (Tg) mice expressing an IL-15 cDNA isoform encoding nonsecretable IL-15 protein had an impaired ability to produce IL-15. In this study, we found that expression of endogenous IL-15 mRNA but not tumor necrosis factor alpha mRNA was severely impaired in response to lipopolysaccharide, not only in macrophages from alternative IL-15 Tg mice but also in RAW264.7 cells that had been transfected with alternative IL-15 together with IL-15 receptor alpha (IL-15Ralpha). IL-15 promoter activity was suppressed in the transfected cells. Although nuclear factor-kappaB activation was not impaired, the binding activity of nuclear extracts to the interferon-stimulated response element of the IL-15 promoter region was reduced in RAW264.7 cells, which had been cotransfected with alternative IL-15 and IL-15Ralpha. IL-15 was mainly colocalized with IL-15Ralpha at the cytoplasmic membrane of RAW264.7 cells, which had been cotransfected with normal IL-15, whereas nonsecretable IL-15 was colocalized with IL-15Ralpha in nucleus after cotransfection with alternative IL-15 and IL-15Ralpha. These results suggest that nonsecretable IL-15 generated by alternative splicing suppresses further IL-15 gene transcription, implying a novel autocrine regulatory mechanism for cytokine gene expression by alternative splicing.
Nishimura
Hitoshi
H
Division of Host Defense, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. nishihit@bioreg.kyushu-u.ac.jp
Fujimoto
Atsushi
A
Tamura
Naoyuki
N
Yajima
Toshiki
T
Wajjwalku
Worawidh
W
Yoshikai
Yasunobu
Y
D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics; D006706:Homeostasis / Q000235:genetics*; D019409:Interleukin-15 / Q000235:genetics* / Q000378:metabolism*; D042541:Intracellular Space / Q000737:chemistry; D008264:Macrophages / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2; D015398:Signal Transduction / Q000235:genetics; D051197:Toll-Like Receptor 4; D015533:Transcriptional Activation / Q000235:genetics*
D004268:DNA-Binding Proteins; C508025:Il15ra protein, mouse; D019409:Interleukin-15; D020033:Protein Isoforms; D011971:Receptors, Immunologic; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D004247:DNA