Dpc4 transcriptional activation and dysfunction in cancer cells.
Dpc4 (Smad4) is implicated in mediation of signals from transforming growth factor (TGF) beta and related ligands, and wild-type Dpc4 mediates TGF-beta-stimulated gene transcription at specific DNA sequences bound by Dpc4 [Smad binding element (SBE)]. We characterized panels of DPC4 tumor mutations and cancer cell lines. Amino acid substitutions within the NH2-terminal third of Dpc4 weakened or ablated SBE-mediated gene regulation by a disruption of DNA binding. An interaction of the COOH-terminal end with the DNA-binding domain of Dpc4 was evident but was not required to explain the functional impairment produced by NH2-terminal DPC4 mutations. Both substitution and truncation mutations of the COOH-terminal half of DPC4 lacked the ability to regulate transcription while retaining the sequence-specific DNA-binding function, but through differing mechanisms. A modular domain to redistribute Dpc4 to the nuclear compartment allowed SBE-mediated transcriptional activation in a cell line having a TGF-1 receptor defect and was sufficient to restore SBE-mediated transactivation ability to COOH-terminal DPC4 missense mutants. Cells harboring DPC4 alterations had a universal impairment of the TGF-beta-stimulated SBE transcriptional response. These studies identify the loss of SBE-mediated gene regulation as a uniform outcome of the selection for DPC4 alterations during tumorigenesis. They raise the possibility of restoration of some Dpc4-associated transcriptional events in cancer cells through the targeted redistribution of wild-type and some missense mutant forms of Dpc4 to the nucleus.
Dai
J L
JL
Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205-2196, USA.
Turnacioglu
K K
KK
Schutte
M
M
Sugar
A Y
AY
Kern
S E
SE
D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D009154:Mutation; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D051901:Smad4 Protein; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000502:physiology*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D004247:DNA