Runt-related transcription factor 1 (RUNX1) stimulates tumor suppressor p53 protein in response to DNA damage through complex formation and acetylation.

Representative tumor suppressor p53 plays a critical role in the regulation of proper DNA damage response. In this study, we have found for the first time that Runt-related transcription factor 1 (RUNX1) contributes to p53-dependent DNA damage response. Upon adriamycin (ADR) exposure, p53 as well as RUNX1 were strongly induced in p53-proficient HCT116 and U2OS cells, which were closely associated with significant transactivation of p53 target genes, such as p21(WAF)(1), BAX, NOXA, and PUMA. RUNX1 was exclusively expressed in the cell nucleus and formed a complex with p53 in response to ADR. Chromatin immunoprecipitation assay demonstrated that p53 together with RUNX1 are efficiently recruited onto p53 target gene promoters following ADR exposure, indicating that RUNX1 is involved in p53-mediated transcriptional regulation. Indeed, forced expression of RUNX1 stimulated the transcriptional activity of p53 in response to ADR. Consistent with these observations, knockdown of RUNX1 attenuated ADR-mediated induction of p53 target genes and suppressed ADR-dependent apoptosis. Furthermore, RUNX1 was associated with p300 histone acetyltransferase, and ADR-dependent acetylation of p53 at Lys-373/382 was markedly inhibited in RUNX1 knockdown cells. In addition, knockdown of RUNX1 resulted in a significant decrease in the amount of p53-p300 complex following ADR exposure. Taken together, our present results strongly suggest that RUNX1 is required for the stimulation of p53 in response to DNA damage and also provide novel insight into understanding the molecular mechanisms behind p53-dependent DNA damage response.

Co-chaperon DnaJC7/TPR2 enhances p53 stability and activity through blocking the complex formation between p53 and MDM2.

Tumor suppressor p53 plays a critical role in the regulation of DNA damage response. Upon severe DNA damage, p53 promotes apoptosis to eliminate cells with seriously damaged DNA to maintain genomic integrity. Pro-apoptotic function of p53 is tightly linked to its sequence-specific transactivation ability. In the present study, we have identified co-chaperon DnaJC7/TPR2 as a novel binding partner of p53 by yeast-based two-hybrid screening. In the two-hybrid screening, we used the central DNA-binding domain of p53 as a bait. Co-immunoprecipitation experiments demonstrated that DnaJC7 is associated with p53 in mammalian cells. Luciferase reporter and colony formation assays revealed that DnaJC7 enhances p53-dependent transcriptional as well as growth-suppressive activity. Forced expression of DnaJC7 induced to extend a half-life of p53, indicating that DnaJC7-mediated activation of p53 might be at least in part due to its prolonged half-life. Consistent with these observations, the amount of p53/MDM2 complex was markedly reduced in the presence of DnaJC7, suggesting that DnaJC7 dissociates MDM2 from p53. Taken together, our present findings strongly suggest that DnaJC7 participates in p53/MDM2 negative feedback regulatory pathway, and thereby enhancing the stability and activity of p53.

Inhibitory role of E2F-1 in the regulation of tumor suppressor p53 during DNA damage response.

Appropriate regulation of DNA damage response is pivotal for maintaining genome stability. p53 as well as E2F-1 plays a critical role during DNA damage response, however, the physiological significance of their interaction has been elusive. In the present study, we found that E2F-1 has an inhibitory effect on p53 during adriamycin (ADR)-mediated DNA damage response. Upon ADR exposure, p53 and E2F-1 were markedly induced at protein and mRNA levels in p53-procifient U2OS and HCT116 cells, and formed a stable complex as examined by co-immunoprecipitation experiments. Of note, chromatin immunoprecipitation (ChIP) experiments revealed that ADR-mediated induction coincides with the efficient recruitment of p53 and E2F-1 onto the promoters of p53-target genes, such as p21(WAF1) and BAX. Subsequent RT-PCR and luciferase reporter assays demonstrated that E2F-1 strongly attenuates p53-dependent transactivation of p53-target genes. Importantly, siRNA-mediated knockdown of E2F-1 stimulated apoptosis in response to ADR, which was associated with an accelerated response of p21(WAF1) and BAX. Collectively, our present findings suggest that E2F-1 participates in p53-mediated DNA damage response and might have a checkpoint function to limit overactive p53.

[A case of interstitial lung diseases in patient treated with oxaliplatin, 5-fluorouracil and leucovorin (FOLFOX)].

FOLFOX/bevacizumab has been shown to be a promising chemotherapeutic regimen for advanced or metastatic colorectral cancer. We reported a case of intestinal lung diseases occurring in association with the use of this combination chemotherapy. The patient presented here is a 71-year-old man with lung metastasis of rectal cancer who was treated with FOLFOX4/ bevacizumab. He complained of high fever in the eleventh course of a FOLFOX4/bevacizumab regimen. Chemotherapy was stopped. But fourteen days after, he suffered from dyspnea and soon went into respiratory failure of WHO grade 3 with severe hypoxemia. He was diagnosed with interstitial pneumonitis. Corticosteroid therapy consisting of metylprednisolone(1 g/day) for tree days was significantly effective in treatment of respiratory failure. Drug-induced interstitial pneumonitis was suspected from chest X-ray and CT. We performed DLST of oxaliplatin, l-levofolinate, 5-FU and bevacizumab for him. He was positive for oxaliplatin and l-levofolinate and 5-FU, and negative for bevacizumab. Interstitial pneumonitis induced by FOLFOX/bevacizumab chemotherapy is rare, but six patients had developed, one of whom died in post-marketing surveillance. The possibility of interstitial pneumonitis should always be considered when a patient presents with a respiratory disorder while undergoing systemic chemotherapy.