Roles of CREB-binding protein (CBP)/p300 in respiratory epithelium tumorigenesis

CREB-binding protein （CBP） and its homologue p300 are transcriptional co-activators of various sequence-specific transcription factors that are involved in a wide array of cellular activities, such as DNA repair, cell growth, differentia- tion and apoptosis. Several studies have suggested that CBP and p300 might be considered as tumour suppressors, with their prominent role being the cross-coupling of distinct gene expression patterns in response to various stimuli. They exert their actions mainly via acetylation of histones and other regulatory proteins （e.g. p53）. A major paradox in CBP/ p300 function is that they seem capable of contributing to various opposed cellular processes. Respiratory epithelium tumorigenesis represents a complex process of multi-step accumulations of a gamut of genetic and epigenetic aberrations. Transcription modulation through the alternate formation of activating and repressive complexes is the ultimate converging point of these derangements, and CBP/p300 represents key participants in this interplay. Thus, illumination of their molecular actions and interactions could reveal new potential targets for pharmacological interventions in respiratory epithelium carcinogenesis.

Role of Acetylated p53 in Regulating the Expression of map2 in Retinoic Acid-induced P19 Cells

Objective To investigate the regulatory mechanisms of acetylated p53 in the expression of microtubule-associated protein-2(MAP2) in neuronal differentiation of P19 cells induced by all-trans retinoic acid(RA).Methods Neuronal differentiation of P19 cells was initiated with 4-day RA treatment.Immunofluorescence,real-time reverse transcription-polymerase chain reaction(RT-PCR) assay,and map2 promoter driven luciferase assay were performed to detect the expression and relative promoter activity of MAP2 in those RA-treated cells.Real-time PCR-based chromatin immunoprecipitation assay(ChIP) was carried out to reveal the specific recruitment of acetylated p53 onto its binding sites on map2 promoter.Results The expression of MAP2 was markedly increased in RA-induced P19 cells.The map2 mRNA increased 34-fold after 4 days of RA treatment and 730-fold 2 days after the treatment,compared with the cells without RA treatment(control).p53 was recruited to the promoter of map2 gene in acetylated form and thereby enhanced its promoter activity.p300/CBP associated factor(PCAF) was found induced in RA-treated cells and enriched in the nucleus,which might contribute to the acetylation of p53 in the regulation of map2 gene.Conclusions Acetylated p53 may participate in regulating the expression of map2 in RA-induced differentiation of P19 cells.PCAF is possibly involved in this process by mediating the acetylation of p53.

CITED2 and the modulation of the hypoxic response in cancer

CITED2(CBP/p300-interacting transactivator with Glu/Asp-rich C-terminal domain,2)is a ubiquitously expressed protein exhibiting a high affinity for the CH1 domain of the transcriptional co-activators CBP/p300,for which it competes with hypoxia-inducible factors(HIFs).CITED2 is particularly efficient in the inhibition of HIF-1α-dependent transcription in different contexts,ranging from organ development and metabolic homeostasis to tissue regeneration and immunity,being also potentially involved in various other physiological processes.In addition,CITED2 plays an important role in inhibiting HIF in some diseases,including kidney and heart diseases and type 2-diabetes.In the particular case of cancer,CITED2 either functions by promoting or suppressing cancer development depending on the context and type of tumors.For instance,CITED2 overexpression promotes breast and prostate cancers,as well as acute myeloid leukemia,while its expression is downregulated to sustain colorectal cancer and hepatocellular carcinoma.In addition,the role of CITED2 in the maintenance of cancer stem cells reveals its potential as a target in non-small cell lung carcinoma and acute myeloid leukemia,for example.But besides the wide body of evidence linking both CITED2 and HIF signaling to carcinogenesis,little data is available regarding CITED2 role as a negative regulator of HIF-1αspecifically in cancer.Therefore,comprehensive studies exploring further the interactions of these two important mediators in cancer-specific models are sorely needed and this can potentially lead to the development of novel targeted therapies.

Regulation of the cell fate by DNA damage and hypoxia

In order to provide the means for the design of novel rational anti-cancer drug therapies research efforts are concentrated on unravelling the molecular circuits which induce programmed cell death and block proliferation of cancer cells.Modern therapeutic strategies are based on the understanding of the complexity of physiological functions such as differentiation,development,immune responses,cell-cycle arrest,DNA damage repair,apoptosis,autophagy,energy metabolism,and senescence.It has become evident that this knowledge will provide the means to target the components of the pathways involved in these processes in a specific and selective manner thus paving the way for the development of effective and personalised anti-cancer therapies.Transcription is a crucial cellular process that regulates a multitude of physiological functions,which are essential in disease progression and cellular response to therapy.Transcription factors such as the p53 tumor suppressor and the hypoxia-inducible factor-α(HIF-α) are key players in carcinogenesis and cellular response to cancer therapies.Both of these transcription factors regulate gene expression of genes involved in cell death and proliferation,in some cases cooperating towards producing the same outcome and in some others mediating opposing effects.It is thus apparent that fine tuning of the activity of these transcription factors is essential to determine the cellular response to therapeutic regimens,in other words whether tumor cells will commit to apoptosis or evade engagement with the anti-proliferative effects of drugs leading to drug resistance.Our observations support the notion that the functional crosstalk between HIF-1α and p53 pathways and thus the fine tuning of their transcriptional activity is mediated by cofactors shared between the two transcription factors such as components of the p300 co-activator multiprotein complex.In particular,there is evidence to suggest that differential composition of the co-modulatory protein complexes associated with p53 and HIF-la under diverse types of stress conditions differentially regulate the expression of distinct subsets of p53 and HIF-la target genes involved in processes such as cell cycle arrest,apoptosis,chronic inflammation,and cellular energy metabolism thereby determining the cellular fate under particular types of microenvironmental stress.