Che-1 sustains hypoxic response of colorectal cancer cells by affecting Hif-1α stabilization.

BACKGROUND: Solid tumours are less oxygenated than normal tissues. Consequently, cancer cells acquire to be adapted to a hypoxic environment. The poor oxygenation of solid tumours is also a major indicator of an adverse cancer prognosis and leads to resistance to conventional anticancer treatments. We previously showed the involvement of Che-1/AATF (Che-1) in cancer cell survival under stress conditions. Herein we hypothesized that Che-1 plays a role in the response of cancer cells to hypoxia. METHODS: The human colon adenocarcinoma HCT116 and HT29 cell lines undepleted or depleted for Che-1 expression by siRNA, were treated under normoxic and hypoxic conditions to perform studies regarding the role of this protein in metabolic adaptation and cell proliferation. Che-1 expression was detected using western blot assays; cell metabolism was assessed by NMR spectroscopy and functional assays. Additional molecular studies were performed by RNA seq, qRT-PCR and ChIP analyses. RESULTS: Here we report that Che-1 expression is required for the adaptation of cells to hypoxia, playing an important role in metabolic modulation. Indeed, Che-1 depletion impacted on HIF-1α stabilization, thus downregulating the expression of several genes involved in the response to hypoxia and affecting glucose metabolism. CONCLUSIONS: We show that Che-1 a novel player in the regulation of HIF-1α in response to hypoxia. Notably, we found that Che-1 is required for SIAH-2 expression, a member of E3 ubiquitin ligase family that is involved in the degradation of the hydroxylase PHD3, the master regulator of HIF-1α stability.

Che-1-induced inhibition of mTOR pathway enables stress-induced autophagy.

Mammalian target of rapamycin (mTOR) is a key protein kinase that regulates cell growth, metabolism, and autophagy to maintain cellular homeostasis. Its activity is inhibited by adverse conditions, including nutrient limitation, hypoxia, and DNA damage. In this study, we demonstrate that Che-1, a RNA polymerase II-binding protein activated by the DNA damage response, inhibits mTOR activity in response to stress conditions. We found that, under stress, Che-1 induces the expression of two important mTOR inhibitors, Redd1 and Deptor, and that this activity is required for sustaining stress-induced autophagy. Strikingly, Che-1 expression correlates with the progression of multiple myeloma and is required for cell growth and survival, a malignancy characterized by high autophagy response.

Centrosomal Che-1 protein is involved in the regulation of mitosis and DNA damage response by mediating pericentrin (PCNT)-dependent Chk1 protein localization.

To combat threats posed by DNA damage, cells have evolved mechanisms, collectively termed DNA damage response (DDR). These mechanisms detect DNA lesions, signal their presence, and promote their repair. Centrosomes integrate G2/M checkpoint control and repair signals in response to genotoxic stress, acting as an efficient control mechanism when G2/M checkpoint function fails and mitosis begins in the presence of damaged DNA. Che-1 is an RNA polymerase II-binding protein involved in the regulation of gene transcription, induction of cell proliferation, and DDR. Here we provide evidence that in addition to its nuclear localization, Che-1 localizes at interphase centrosomes, where it accumulates following DNA damage or spindle poisons. We show that Che-1 depletion generates supernumerary centrosomes, multinucleated cells, and multipolar spindle formation. Notably, Che-1 depletion abolishes the ability of Chk1 to bind pericentrin and to localize at centrosomes, which, in its turn, deregulates the activation of centrosomal cyclin B-Cdk1 and advances entry into mitosis. Our results reinforce the notion that Che-1 plays an important role in DDR and that its contribution seems to be relevant for the spindle assembly checkpoint.

Che-1 promotes tumor cell survival by sustaining mutant p53 transcription and inhibiting DNA damage response activation.

Che-1 is a RNA polymerase II binding protein involved in the regulation of gene transcription and, in response to DNA damage, promotes p53 transcription. In this study, we investigated whether Che-1 regulates mutant p53 expression. We found that Che-1 is required for sustaining mutant p53 expression in several cancer cell lines, and that Che-1 depletion by siRNA induces apoptosis both in vitro and in vivo. Notably, loss of Che-1 activates DNA damage checkpoint response and induces transactivation of p73. Therefore, these findings underline the important role that Che-1 has in survival of cells expressing mutant p53.

Novel activation domain derived from Che-1 cofactor coupled with the artificial protein Jazz drives utrophin upregulation.

Our aim is to upregulate the expression level of the dystrophin related gene utrophin in Duchenne muscular dystrophy, thus complementing the lack of dystrophin functions. To this end, we have engineered synthetic zinc finger based transcription factors. We have previously shown that the artificial three-zinc finger protein named Jazz fused with the Vp16 activation domain, is able to bind utrophin promoter A and to increase the endogenous level of utrophin in transgenic mice. Here, we report on an innovative artificial protein, named CJ7, that consists of Jazz DNA binding domain fused to a novel activation domain derived from the regulatory multivalent adaptor protein Che-1/AATF. This transcriptional activation domain is 100 amino acids in size and it is very powerful as compared to the Vp16 activation domain. We show that CJ7 protein efficiently promotes transcription and accumulation of the acetylated form of histone H3 on the genomic utrophin promoter locus.

Utrophin up-regulation by an artificial transcription factor in transgenic mice.

Duchenne Muscular Dystrophy (DMD) is a severe muscle degenerative disease, due to absence of dystrophin. There is currently no effective treatment for DMD. Our aim is to up-regulate the expression level of the dystrophin related gene utrophin in DMD, complementing in this way the lack of dystrophin functions. To this end we designed and engineered several synthetic zinc finger based transcription factors. In particular, we have previously shown that the artificial three zinc finger protein named Jazz, fused with the appropriate effector domain, is able to drive the transcription of a test gene from the utrophin promoter "A". Here we report on the characterization of Vp16-Jazz-transgenic mice that specifically over-express the utrophin gene at the muscular level. A Chromatin Immunoprecipitation assay (ChIP) demonstrated the effective access/binding of the Jazz protein to active chromatin in mouse muscle and Vp16-Jazz was shown to be able to up-regulate endogenous utrophin gene expression by immunohistochemistry, western blot analyses and real-time PCR. To our knowledge, this is the first example of a transgenic mouse expressing an artificial gene coding for a zinc finger based transcription factor. The achievement of Vp16-Jazz transgenic mice validates the strategy of transcriptional targeting of endogenous genes and could represent an exclusive animal model for use in drug discovery and therapeutics.

The artificial 4-zinc-finger protein Bagly binds human utrophin promoter A at the endogenous chromosomal site and activates transcription.

Our aim is to upregulate the expression of the dystrophin-related gene utrophin in Duchenne muscular dystrophy, in this way complementing the lack of dystrophin function. To achieve utrophin upregulation, we designed and engineered synthetic zinc-finger based transcription factors. We have previously shown that the artificial 3-zinc-finger protein Jazz, fused with the appropriate effector domain, is able to drive the transcription of a test gene from utrophin promoter A. Here we report a novel artificial 4-zinc-finger protein, Bagly, which binds with optimized affinity-specificity to a 12 bp DNA target sequence that is internal to human utrophin promoter A. Bagly was generated adding to Jazz protein an extra-fourth zinc finger, derived from transcription factor YY1. Importantly, the Bagly DNA target sequence is statistically present in the human genome only 210 times, about 60 fewer times than the 9 bp Jazz DNA target sequence. Thanks to its additional zinc-finger domain, Bagly protein shows enhanced transcriptional activity. Moreover, we demonstrated Bagly's effective access and binding to active chromatin in the chromosomal context and its ability to upregulate endogenous utrophin.

NRAGE associates with the anti-apoptotic factor Che-1 and regulates its degradation to induce cell death.

Neurotrophin receptor-interacting MAGE homolog (NRAGE) has been recently identified as a cell-death inducer, involved in molecular events driving cells through apoptotic networks during neuronal development. Recently, we have focused on the functional role of Che-1, also known as apoptosis-antagonizing transcription factor (AATF), a protein involved in cell cycle control and gene transcription. Increasing evidence suggests that Che-1 is involved in apoptotic signalling in neural tissues. In cortical neurons Che-1 exhibits an anti-apoptotic activity, protecting cells from neuronal damage induced by amyloid beta-peptide. Here, we report that Che-1 interacts with NRAGE and that an EGFP-NRAGE fusion protein inhibits nuclear localization of Che-1, by sequestering it within the cytoplasmic compartment. Furthermore, NRAGE overexpression downregulates endogenous Che-1 by targeting it for proteasome-dependent degradation. Finally, we propose that Che-1 is a functional antagonist of NRAGE, because its overexpression completely reverts NRAGE-induced cell-death.