PKC delta mediates ionizing radiation-induced activation of c-Jun NH(2)-terminal kinase through MKK7 in human thyroid cells.
The thyroid gland is one of the most sensitive organs in ionizing radiation (IR)-induced carcinogenesis. To determine, therefore, the specific cascade of IR-induced signal transduction in human thyroid cells, we investigated the functional role of protein kinase C (PKC), especially its interlocking activation of c-Jun NH(2)-terminal kinase (JNK) pathway. In the present study, using adenovirus expression vectors for diverse dominant-negative (DN) types of PKC isoforms (alpha, beta2, delta, epsilon and zeta) expressed in primary cultured human thyroid cells, only DN/PKC delta suppressed IR-induced JNK activation. In addition, Rottlerin, a PKC delta specific inhibitor, inhibited IR-induced JNK activation. IR-induced activation of transcription factor AP-1, downstream target of JNK, was also attenuated by DN/PKC delta. To examine the involvement of upstream kinases of JNK, we performed immune-complex kinase assays of mitogen-activated protein kinase kinase 4 (MKK4) and MKK7. IR activated MKK7 but not MKK4, and this activation was inhibited by Rottlerin. Furthermore, IR-induced JNK activation was suppressed by overexpression of kinase-deficient MKK7. Our results indicate that IR selectively activates the cascade of PKC delta-MKK7-JNK-AP-1 in human thyroid cells, suggesting a not apoptotic but radio-resistant role of PKC delta in human thyroid cells following IR.
Mitsutake
N
N
Department of Nature Medicine, Atomic Bomb Disease Institute, Nagasaki University School of Medicine, Nagasaki 852-8523, Japan.
Namba
H
H
Shklyaev
S S
SS
Tsukazaki
T
T
Ohtsuru
A
A
Ohba
M
M
Kuroki
T
T
Ayabe
H
H
Yamashita
S
S
D004789:Enzyme Activation; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D048688:MAP Kinase Kinase 7; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051745:Protein Kinase C-delta; D011839:Radiation, Ionizing; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013961:Thyroid Gland / Q000528:radiation effects*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014466:Ultraviolet Rays; D014965:X-Rays
D007527:Isoenzymes; D018808:Transcription Factor AP-1; D014443:Tyrosine; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D048688:MAP Kinase Kinase 7; C482559:MAP2K4 protein, human; C482569:MAP2K7 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases