Differential regulation of the REGγ–proteasome pathway by p53/TGF-β signalling and mutant p53 in cancer cells

Abstract

Proteasome activity is frequently enhanced in cancer to accelerate metastasis and tumorigenesis. REGγ, a proteasome activator known to promote p53/p21/p16 degradation, is often overexpressed in cancer cells. Here we show that p53/TGF-β signalling inhibits the REGγ–20S proteasome pathway by repressing REGγ expression. Smad3 and p53 interact on the REGγ promoter via the p53RE/SBE region. Conversely, mutant p53 binds to the REGγ promoter and recruits p300. Importantly, mutant p53 prevents Smad3/N-CoR complex formation on the REGγ promoter, which enhances the activity of the REGγ–20S proteasome pathway and contributes to mutant p53 gain of function. Depletion of REGγ alters the cellular response to p53/TGF-β signalling in drug resistance, proliferation, cell cycle progression and proteasome activity. Moreover, p53 mutations show a positive correlation with REGγ expression in cancer samples. These findings suggest that targeting REGγ–20S proteasome for cancer therapy may be applicable to human tumours with abnormal p53/Smad protein status. Furthermore, this study demonstrates a link between p53/TGF-β signalling and the REGγ–20S proteasome pathway, and provides insight into the REGγ/p53 feedback loop.

REGγ is critical for skin carcinogenesis by modulating the Wnt/β-catenin pathway

“…ChIP primer sequences are as follows: forward: 5 0 -CATGTT GAAATACTTGTA-3 0 ; reverse: 5 0 -TCTTCATGCACCCATTCA-3 0 . Electrophoretic mobility shift assay was performed as described 44 . The probe for electrophoretic mobility shift assay was labelled with FAM fluorescence.…”

Tumor-suppressive p53 Signaling Empowers Metastatic Inhibitor KLF17-dependent Transcription to Overcome Tumorigenesis in Non-small Cell Lung Cancer

“…Cell Culture and Treatments-H1299 and A549 cells were described previously in our study (33). For cell treatments, we used Nutlin-3 (10 M) (Sigma-Aldrich), Adriamycin (0.5 M) (Sigma-Aldrich), and etoposide (10 M) (Sigma-Aldrich).…”

“…Plasmids and Transfection-pcDNA3.1-p53 plasmid was described in our previous study (33). H1299 and A549 lung cancer cell lines were transfected with Lipofectamine 2000 following the manufacturer's protocol (Invitrogen).…”

Mutant p53 Promotes Tumor Cell Malignancy by Both Positive and Negative Regulation of the Transforming Growth Factor β (TGF-β) Pathway

“…The Smad2 and Smad3 truncations were amplified from pRK5-Smad2 and pRK5-Smad3 by PCR and constructed into the pCDNA3.1 vector. caMEK1 and HA-ERK1 (27).…”

“…Electrophoretic Mobility Shift Assay-DNA-binding assays for Smad3/Smad4 were performed following protocols described previously (27,31,32). Briefly, 32 P-labeled doublestranded SBE oligonucleotides from the p21waf1 gene promoter region were used as probes, and competition assays were performed with a 100-fold excess of unlabeled wild-type or mutant SBE oligonucleotides (31).…”