SCF(beta-TrCP1) controls Smad4 protein stability in pancreatic cancer cells.
Smad4, also known as deleted in pancreatic carcinoma locus 4 (DPC4), is a critical co-factor in signal transduction pathways activated by transforming growth factor (TGF)-beta-related ligands that regulate cell growth and differentiation. Mutations in Smad4/DPC4 have been identified in approximately 50% of pancreatic adenocarcinomas. Here we report that SCF(beta-TrCP1), a ubiquitin (E3) ligase, is a critical determinant for Smad4 protein degradation in pancreatic cancer cells. We found that F-box protein beta-TrCP1 in this E3 ligase interacted with Smad4 and that SCF(beta-TrCP1) inhibited TGF-beta biological activity in pancreatic cancer cells by decreasing Smad4 stability. Very low Smad4 protein levels in human pancreatic ductal adenocarcinoma cells were observed by immunohistochemistry. By analyzing pancreatic tumor-derived Smad4 mutants, we found that most point-mutated Smad4 proteins, except those within or very close to a mutation cluster region, exhibited higher interaction affinity with beta-TrCP1 and significantly elevated protein ubiquitination by SCF(beta-TrCP1). Furthermore, AsPC-1 and Caco-2, two cancer cell lines harboring Smad4 point mutations, exhibited rapid Smad4 protein degradation due to the effect of SCF(beta-TrCP1). Both Smad4 levels and TGF-beta signaling were elevated by retrovirus-delivered beta-TrCP1 siRNA in pancreatic cancer cells. Therefore, inhibition of Smad4-specific E3 ligase might be a target for therapeutic intervention in pancreatic cancer.
Wan
Mei
M
Department of Pathology, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA. mwan@path.uab.edu
Huang
Jin
J
Jhala
Nirag C
NC
Tytler
Ewan M
EM
Yang
Lei
L
Vickers
Selwyn M
SM
Tang
Yi
Y
Lu
Chongyuan
C
Wang
Ning
N
Cao
Xu
X
D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D000368:Aged; D000369:Aged, 80 and over; D018270:Carcinoma, Ductal, Breast / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004355:Drug Stability; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D017354:Point Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism* / Q000494:pharmacology; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors; D025801:Ubiquitin / Q000378:metabolism
D004268:DNA-Binding Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D025801:Ubiquitin; D044843:SKP Cullin F-Box Protein Ligases; D046988:Proteasome Endopeptidase Complex