A complex pattern of mutations and abnormal splicing of Smad4 is present in thyroid tumours.
Sensitivity to transforming growth factor-beta is impaired in thyroid tumours. Similar to Mad -- Mother Against Decapentaplegic-(Smad)4 is frequently altered in cancers, but its involvement in this system is unknown. We analysed 56 thyroid tumours of various histotypes for Smad4 mutations by PCR-SSCP and sequencing, linking them to Smad4 reactivity as examined by immunohistochemistry (IHC), and 29 of them also for abnormalities in RNA expression due to alternative splicing. In all, 15/56 cases (27%), both benign and malignant lesions, harbour alterations of Smad4 coding sequence. We found several novel intragenic mutations (13 missense, two silent, one frameshift and one large insertion-deletion), with high incidence in the linker region. A subset of mutated tumours failed to express Smad4 protein by IHC. We have also detected four alternatively spliced tumour-associated Smad4 isoforms, lacking portions of the linker region, and three more due to unreported internal exon-exon rearrangements. Smad4 is both frequently mutated and deregulated by aberrant splicing in thyroid tumours and these alterations may contribute as an early event to thyroid tumorigenesis.
Lazzereschi
Davide
D
Department of Experimental Medicine and Pathology, I Faculty of Medicine, University of Rome 'La Sapienza', V.le Regina Elena 324, Rome 00161, Italy. davide.lazzereschi@uniroma1.it
Nardi
Francesco
F
Turco
Alessandra
A
Ottini
Laura
L
D'Amico
Cristina
C
Mariani-Costantini
Renato
R
Gulino
Alberto
A
Coppa
Anna
A
D017398:Alternative Splicing; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics*; D006801:Humans; D018807:Polymorphism, Single-Stranded Conformational; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051901:Smad4 Protein; D013964:Thyroid Neoplasms / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000502:physiology
D004268:DNA-Binding Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta