Acceleration of Smad2 and Smad3 phosphorylation via c-Jun NH(2)-terminal kinase during human colorectal carcinogenesis.
Conversion of normal epithelial cells to tumors is associated with a shift in transforming growth factor-beta (TGF-beta) function: reduction of tumor suppressor activity and increase of oncogenic activity. However, specific mechanisms of this functional alteration during human colorectal carcinogenesis remain to be elucidated. TGF-beta signaling involves Smad2/3 phosphorylated at linker regions (pSmad2/3L) and COOH-terminal regions (pSmad2/3C). Using antibodies specific to each phosphorylation site, we herein showed that Smad2 and Smad3 were phosphorylated at COOH-terminal regions but not at linker regions in normal colorectal epithelial cells and that pSmad2/3C were located predominantly in their nuclei. However, the linker regions of Smad2 and Smad3 were phosphorylated in 31 sporadic colorectal adenocarcinomas. In particular, late-stage invasive and metastatic cancers typically showed a high degree of phosphorylation of Smad2/3L. Their extent of phosphorylation in 11 adenomas was intermediate between those in normal epithelial cells and adenocarcinomas. Whereas pSmad2L remained in the cytoplasm, pSmad3L was located exclusively in the nuclei of Ki-67-immunoreactive adenocarcinomas. In contrast, pSmad3C gradually decreased as the tumor stage progressed. Activated c-Jun NH(2)-terminal kinase in cancers could directly phosphorylate Smad2/3L. Although Mad homology 2 region sequencing in the Smad4 gene revealed a G/A substitution at codon 361 in one adenocarcinoma, the mutation did not correlate with phosphorylation. No mutations in the type II TGF-beta receptor and Smad2 genes were observed in the tumors. In conclusion, pSmad3C, which favors tumor suppressor activity of TGF-beta, was found to decrease, whereas c-Jun NH(2)-terminal kinase tended to induce the phosphorylation of Smad2/3L in human colorectal adenoma-carcinoma sequence.
Yamagata
Hideo
H
Third Department of Internal Medicine, Kansai Medical University, Osaka, Japan.
Matsuzaki
Koichi
K
Mori
Shigeo
S
Yoshida
Katsunori
K
Tahashi
Yoshiya
Y
Furukawa
Fukiko
F
Sekimoto
Go
G
Watanabe
Toshihiko
T
Uemura
Yoshiko
Y
Sakaida
Noriko
N
Yoshioka
Kazuhiko
K
Kamiyama
Yasuo
Y
Seki
Toshihito
T
Okazaki
Kazuichi
K
D000230:Adenocarcinoma / Q000473:pathology; D001665:Binding Sites; D002471:Cell Transformation, Neoplastic; D015179:Colorectal Neoplasms / Q000473:pathology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009367:Neoplasm Staging; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D004268:DNA-Binding Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D048031:JNK Mitogen-Activated Protein Kinases