A mutant form of JAB/SOCS1 augments the cytokine-induced JAK/STAT pathway by accelerating degradation of wild-type JAB/CIS family proteins through the SOCS-box.
Cytokines exert biological functions by activating Janus tyrosine kinases (JAKs), and JAK inhibitors JAB (also referred to as SOCS1 and SSI1) and CIS3 (SOCS3) play an essential role in the negative regulation of cytokine signaling. We have found that transgenic (Tg) mice expressing a mutant JAB (F59D-JAB) exhibited a more potent STAT3 activation and a more severe colitis than did wild-type littermates after treatment with dextran sulfate sodium. We now find that there is a prolonged activation of JAKs and STATs in response to a number of cytokines in T cells from Tg mice with lck promoter-driven F59D-JAB. Overexpression of F59D-JAB also sustained activation of JAK2 in Ba/F3 cells. These data suggested that F59D-JAB up-regulated STAT activity by sustaining JAK activation. To elucidate molecular mechanisms related to F59D-JAB, we analyzed the effects of F59D-JAB on the JAK/STAT pathway using the 293 cell transient expression system. We found that the C-terminal SOCS-box played an essential role in augmenting cytokine signaling by F59D-JAB. The SOCS-box interacted with the Elongin BC complex, and this interaction stabilized JAB. F59D-JAB induced destabilization of wild-type JAB, whereas overexpression of Elongin BC canceled this effect. Levels of endogenous JAB and CIS3 in T cells from F59D-JAB Tg-mouse were lower than in wild-type mice. We propose that F59D-JAB destabilizes wild-type, endogenous JAB and CIS3 by chelating the Elongin BC complex, thereby sustaining JAK activation.
Hanada
T
T
Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Yoshida
T
T
Kinjyo
I
I
Minoguchi
S
S
Yasukawa
H
H
Kato
S
S
Mimata
H
H
Nomura
Y
Y
Seki
Y
Y
Kubo
M
M
Yoshimura
A
A
D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D016207:Cytokines / Q000502:physiology*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D047908:Intracellular Signaling Peptides and Proteins; D009154:Mutation; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology
D002352:Carrier Proteins; D016207:Cytokines; D017931:DNA Primers; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C491590:Socs1 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases