Smad4-dependent TGF-beta signaling suppresses RON receptor tyrosine kinase-dependent motility and invasion of pancreatic cancer cells.
Transforming growth factorbeta (TGF-beta) signals through Smad-dependent and Smad-independent pathways. However, Smad signaling is altered by allelic deletion or intragenic mutation of the Smad4 gene in more than half of pancreatic ductal adenocarcinomas. We show here that loss of Smad4-dependent signaling leads to aberrant expression of RON, a phosphotyrosine kinase receptor, and that signaling by RON cooperates with Smad4-independent TGF-beta signaling to promote cell motility and invasion. Restoring Smad4 expression in a pancreatic ductal adenocarcinoma cell line that is deficient in Smad4 repressed RON expression. Conversely, small interference RNA knock down of Smad4 or blocking TGF-beta signaling with a TGF-beta type I receptor kinase inhibitor in Smad4-intact cell lines induced RON expression. TGF-beta-induced motility and invasion were inhibited in cells that express Smad4 and that have low levels of RON compared with isogenically matched cells that were deficient in Smad4. Furthermore, knocking down RON expression in Smad4-deficient cells suppressed TGF-beta-mediated motility and invasion. We further determined that Smad4-dependent signaling regulated RON expression at the transcriptional level by real-time reverse transcription PCR and RON promoter luciferase reporter assays. Functional inactivation by site-directed mutations of two Smad binding sites on the RON promoter inhibited TGF-beta-mediated repression of RON promoter activity. These studies indicate that loss of Smad4 contributes to aberrant RON expression and that cross-talk of Smad4-independent TGF-beta signaling and the RON pathway promotes an invasive phenotype.
Zhao
Shujie
S
Department of Medicine, Division of Medical Oncology, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
Ammanamanchi
Sudhakar
S
Brattain
Michael
M
Cao
Lin
L
Thangasamy
Amalraj
A
Wang
Jing
J
Freeman
James W
JW
D000483:Alleles; D002460:Cell Line; D002465:Cell Movement; D017353:Gene Deletion; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009361:Neoplasm Invasiveness; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D010641:Phenotype; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D051901:Smad4 Protein / Q000378:metabolism*; D015534:Trans-Activators; D016212:Transforming Growth Factor beta / Q000378:metabolism*
C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C080835:RON protein; D020794:Receptor Protein-Tyrosine Kinases