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Acceleration of Smad2 and Smad3 phosphorylation via c-Jun NH(2)-terminal kinase during human colorectal

Hideo Yamagata1, Koichi Matsuzaki, Shigeo Mori

  • 1Third Department of Internal Medicine, Kansai Medical University, Osaka, Japan.

Cancer Research
|January 25, 2005
PubMed

Insights

Transforming growth factor-beta (TGF-beta) function shifts during colorectal cancer development. Phosphorylation changes in Smad2/3 linker regions (pSmad2/3L) and COOH-terminal regions (pSmad3C) correlate with tumor progression and altered TGF-beta activity.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cellular Signaling

Background:

  • Transforming growth factor-beta (TGF-beta) normally suppresses tumors, but its function shifts to promote cancer in colorectal carcinogenesis.
  • The precise molecular mechanisms behind this functional alteration in human colorectal cancer remain unclear.
  • TGF-beta signaling relies on Smad2 and Smad3 proteins, which can be phosphorylated at different sites, including linker (L) and COOH-terminal (C) regions.

Purpose of the Study:

  • To investigate the specific phosphorylation patterns of Smad2 and Smad3 during human colorectal carcinogenesis.
  • To elucidate the roles of linker region phosphorylation (pSmad2/3L) and COOH-terminal region phosphorylation (pSmad2/3C) in tumor progression.
  • To identify potential signaling pathways, such as c-Jun N-terminal kinase (JNK), involved in altered Smad phosphorylation.

Main Methods:

  • Utilized antibodies specific to linker and COOH-terminal phosphorylation sites of Smad2 and Smad3.
  • Analyzed phosphorylation status and subcellular localization in normal colorectal cells, adenomas, and adenocarcinomas.
  • Performed sequencing for mutations in Smad4, TGF-beta type II receptor, and Smad2 genes.
  • Investigated the role of activated c-Jun N-terminal kinase (JNK) in Smad phosphorylation.

Main Results:

  • Normal cells showed COOH-terminal phosphorylation (pSmad2/3C) predominantly in the nucleus, with no linker phosphorylation.
  • Colorectal adenocarcinomas exhibited increased linker region phosphorylation (pSmad2/3L), particularly in advanced, metastatic cancers.
  • pSmad3C levels decreased with tumor stage progression, while pSmad3L localized to the nucleus in Ki-67-positive adenocarcinomas.
  • Activated JNK was found to directly phosphorylate Smad2/3 linker regions.
  • No significant correlation was observed between Smad4 codon 361 mutation and phosphorylation patterns.

Conclusions:

  • The decrease in pSmad3C, associated with tumor suppressor activity, is a key event in colorectal adenoma-carcinoma sequence.
  • Increased pSmad2/3L, potentially induced by JNK, may contribute to the oncogenic functions of TGF-beta signaling in colorectal cancer.
  • These findings highlight distinct phosphorylation events in Smad proteins as critical determinants of TGF-beta functional shifts during colorectal carcinogenesis.

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