Chromosome Y pericentric heterochromatin is a primary target of HSF1 in male cells.

The heat shock factor 1 (HSF1)-dependent transcriptional activation of human pericentric heterochromatin in heat-shocked cells is the most striking example of transcriptional activation of heterochromatin. Until now, pericentric heterochromatin of chromosome 9 has been identified as the primary target of HSF1, in both normal and tumor heat-shocked cells. Transcriptional awakening of this large genomic region results in the nuclear accumulation of satellite III (SATIII) noncoding RNAs (ncRNAs) and the formation in cis of specific structures known as nuclear stress bodies (nSBs). Here, we show that, in four different male cell lines, including primary human fibroblasts and amniocytes, pericentric heterochromatin of chromosome Y can also serve as a unique primary site of HSF1-dependent heterochromatin transcriptional activation, production of SATIII ncRNA, and nucleation of nuclear stress bodies (nSBs) upon heat shock. Our observation suggests that the chromosomal origin of SATIII transcripts in cells submitted to heat shock is not a determinant factor as such, but that transcription of SATIII repetitive units or the SATIII ncRNA molecules is the critical element of HSF1-dependent transcription activation of constitutive heterochromatin.

Dysfunctional BTN3A together with deregulated immune checkpoints and type I/II IFN dictate defective interplay between pDCs and γδ T cells in melanoma patients, which impacts clinical outcomes.

OBJECTIVES: pDCs and γδ T cells emerge as potent immune players participating in the pathophysiology of cancers, yet still remaining enigmatic while harbouring a promising potential for clinical translations. Despite strategic and closed missions, crosstalk between pDCs and γδ T cells has not been deciphered yet in cancers, especially in melanoma where the long-term control of the tumor still remains a challenge. METHODS: This prompted us to explore the interplay between pDCs and γδ T cells in the context of melanoma, investigating the reciprocal features of pDCs or γδ T cells, the underlying molecular mechanisms and its impact on clinical outcomes. RESULTS: TLRL-activated pDCs from the blood and tumor infiltrate of melanoma patients displayed an impaired ability to activate, to modulate immune checkpoints and trigger the functionality of γδ T cells. Conversely, γδ T cells from the blood or tumor infiltrate of melanoma patients activated by PAg were defective in triggering pDCs' activation and modulation of immune checkpoints, and failed to elicit the functionality of pDCs. Reversion of the dysfunctional cross-talks could be achieved by specific cytokine administration and immune checkpoint targeting. Strikingly, we revealed an increased expression of BTN3A on circulating and tumor-infiltrating pDCs and γδ T cells from melanoma patients, but stressed out the potential impairment of this molecule. CONCLUSION: Our study uncovered that melanoma hijacked the bidirectional interplay between pDCs and γδ T cells to escape from immune control, and revealed BTN3A dysfunction. Such understanding will help harness and synergise the power of these potent immune cells to design new therapeutic approaches exploiting their antitumor potential while counteracting their skewing by tumors to improve patient outcomes.

c-MYC and p53 expression highlight starry-sky pattern as a favourable prognostic feature in R-CHOP-treated diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous entity, in which the first-line treatment currently consists of an immuno-chemotherapy regimen (R-CHOP). However, around 30% of patients will not respond or will relapse. Overexpression of c-MYC or p53 is frequently found in DLBCL, but an association with prognosis remains controversial, as for other biomarkers previously linked with DLBCL aggressivity (CD5, CD23, or BCL2). The aim of this study was to explore the expression of these biomarkers and their correlation with outcome, clinical, or pathological features in a DLBCL cohort. Immunohistochemical (c-MYC, p53, BCL2, CD5, and CD23), morphological ('starry-sky' pattern [SSP]), targeted gene panel sequencing by next-generation sequencing (NGS), and fluorescence in situ hybridisation analyses were performed on tissue microarray blocks for a retrospective cohort of 94 R-CHOP-treated de novo DLBCL. In univariate analyses, p53 overexpression (p53high ) was associated with unfavourable outcome (p = 0.04) and with c-MYC overexpression (p = 0.01), whereas c-MYC overexpression was linked with an SSP (p = 0.004), but only tended towards an inferior prognosis (p = 0.06). Presence of a starry-sky morphology was found to be correlated with better survival in p53high DLBCL (p = 0.03) and/or c-MYC-positive DLBCL (p = 0.002). Furthermore, NGS data revealed that these three variables were associated with somatic mutations (PIM1, TNFRSF14, FOXO1, and B2M) involved in B-cell proliferation, survival, metabolism, and immune signalling. Taken together, these results show that the SSP pattern seems to be a protective factor in high-risk DLBCL subgroups and highlight cell death as a built-in failsafe mechanism to control tumour growth.

CYCLON and NPM1 Cooperate within an Oncogenic Network Predictive of R-CHOP Response in DLBCL.

R-CHOP immuno-chemotherapy significantly improved clinical management of diffuse large B-cell lymphoma (DLBCL). However, 30-40% of DLBCL patients still present a refractory disease or relapse. Most of the prognostic markers identified to date fail to accurately stratify high-risk DLBCL patients. We have previously shown that the nuclear protein CYCLON is associated with DLBCL disease progression and resistance to anti-CD20 immunotherapy in preclinical models. We also recently reported that it also represents a potent predictor of refractory disease and relapse in a retrospective DLBCL cohort. However, only sparse data are available to predict the potential biological role of CYCLON and how it might exert its adverse effects on lymphoma cells. Here, we characterized the protein interaction network of CYCLON, connecting this protein to the nucleolus, RNA processing, MYC signaling and cell cycle progression. Among this network, NPM1, a nucleolar multi-functional protein frequently deregulated in cancer, emerged as another potential target related to treatment resistance in DLBCL. Immunohistochemistry evaluation of CYCLON and NPM1 revealed that their co-expression is strongly related to inferior prognosis in DLBCL. More specifically, alternative sub-cellular localizations of the proteins (extra-nucleolar CYCLON and pan-cellular NPM1) represent independent predictive factors specifically associated to R-CHOP refractory DLBCL patients, which could allow them to be orientated towards risk-adapted or novel targeted therapies.

p14ARF activates a Tip60-dependent and p53-independent ATM/ATR/CHK pathway in response to genotoxic stress.

p14ARF is a tumor suppressor that controls a well-described p53/Mdm2-dependent checkpoint in response to oncogenic signals. Here, new insights into the tumor-suppressive function of p14ARF are provided. We previously showed that p14ARF can induce a p53-independent G2 cell cycle arrest. In this study, we demonstrate that the activation of ATM/ATR/CHK signaling pathways contributes to this G2 checkpoint and highlight the interrelated roles of p14ARF and the Tip60 protein in the initiation of this DNA damage-signaling cascade. We show that Tip60 is a new direct p14ARF binding partner and that its expression is upregulated and required for ATM/CHK2 activation in response to p14ARF. Strikingly, both p14ARF and Tip60 products accumulate following a cell treatment with alkylating agents and are absolutely required for ATM/CHK2 activation in this setting. Moreover, and consistent with p14ARF being a determinant of CHK2 phosphorylation in lung carcinogenesis, a strong correlation between p14ARF and phospho-CHK2 (Thr68) protein expression is observed in human lung tumors (P < 0.00006). Overall, these data point to a novel regulatory pathway that mediates the p53-independent negative-cell-growth control of p14ARF. Inactivation of this pathway is likely to contribute to lung carcinogenesis.

A New Patient-Derived Metastatic Glioblastoma Cell Line: Characterisation and Response to Sodium Selenite Anticancer Agent.

Glioblastoma multiform (GBM) tumors are very heterogeneous, organized in a hierarchical pattern, including cancer stem cells (CSC), and are responsible for development, maintenance, and cancer relapse. Therefore, it is relevant to establish new GBM cell lines with CSC characteristics to develop new treatments. A new human GBM cell line, named R2J, was established from the cerebro-spinal fluid (CSF) of a patient affected by GBM with leptomeningeal metastasis. R2J cells exhibits an abnormal karyotype and form self-renewable spheres in a serum-free medium. Original tumor, R2J, cultured in monolayer (2D) and in spheres showed a persistence expression of CD44, CD56 (except in monolayer), EGFR, Ki67, Nestin, and vimentin. The R2J cell line is tumorigenic and possesses CSC properties. We tested in vitro the anticancer effects of sodium selenite (SS) compared to temozolomide TMZ. SS was absorbed by R2J cells, was cytotoxic, induced an oxidative stress, and arrested cell growth in G2M before inducing both necrosis and apoptosis via caspase-3. SS also modified dimethyl-histone-3-lysine-9 (H3K9m2) levels and decreased histone deacetylase (HDAC) activity, suggesting anti-invasiveness potential. This study highlights the value of this new GBM cell line for preclinical modeling of clinically relevant, patient specific GBM and opens a therapeutic window to test SS to target resistant and recurrent GBM.

HSP27 favors ubiquitination and proteasomal degradation of p27Kip1 and helps S-phase re-entry in stressed cells.

Stress-inducible HSP27 protects cells from death through various mechanisms. We have recently demonstrated that HSP27 can also enhance the degradation of some proteins through the proteasomal pathway. Here, we show that one of these proteins is the cyclin-dependent kinase (Cdk) inhibitor p27Kip1. The ubiquitination and degradation of this protein that favors progression through the cell cycle was previously shown to involve either a Skp2-dependent mechanism,i.e., at the S-/G2-transition, or a KPC (Kip1 ubiquitination-promoting complex)-dependent mechanism, i.e.,at the G0/G1 transition. In this work, we demonstrate that, in response to serum depletion, p27Kip1 cellular content first increases then progressively decreases as cells begin to die. In this stressful condition, HSP27favors p27Kip1 ubiquitination and degradation by the proteasome. A similar observation was made in response to stress induced by the NO donor glyceryl trinitrate (GTN). HSP27-mediated ubiquitination ofp27Kip1 does not require its phosphorylation on Thr187 or Ser-10, nor does it depend on the SCFSkp2 ubiquitin ligase E3 complex. It facilitates the G1/S transition,which suggests that, in stressful conditions, HSP27might render quiescent cells competent to re-enter the cell cycle.

Anticancer properties of sodium selenite in human glioblastoma cell cluster spheroids.

Glioblastoma (GBM) is the most common type of primary tumor of the central nervous system with a poor prognosis, needing the development of new therapeutic drugs. Few studies focused on sodium selenite (SS) effects in cancer cells cultured as multicellular tumor spheroids (MCTS or 3D) closer to in vivo tumor. We investigated SS anticancer effects in three human GBM cell lines cultured in 3D: LN229, U87 (O(6)-methyguanine-DNA-methyltransferase (MGMT) negative) and T98G (MGMT positive). SS absorption was evaluated and the cytotoxicity of SS and temozolomide (TMZ), the standard drug used against GBM, were compared. SS impacts on proliferation, cell death, and invasiveness were evaluated as well as epigenetic modifications by focusing on histone deacetylase (HDAC) activity and dimethyl-histone-3-lysine-9 methylation (H3K9m2), after 24h to 72h SS exposition. SS was absorbed by spheroids and was more cytotoxic than TMZ (i.e., for LN229, the IC50 was 38 fold-more elevated for TMZ than SS, at 72h). SS induced a cell cycle arrest in the S phase and apoptosis via caspase-3. SS decreased carbonic anhydrase-9 (CA9) expression, invasion on a Matrigel matrix and modulated E- and N-Cadherin transcript expressions. SS decreased HDAC activity and modulated H3K9m2 levels. 3D model provides a relevant strategy to screen new drugs and SS is a promising drug against GBM that should now be tested in GBM animal models.

Bromodomain factors of BET family are new essential actors of pericentric heterochromatin transcriptional activation in response to heat shock.

The heat shock response is characterized by the transcriptional activation of both hsp genes and noncoding and repeated satellite III DNA sequences located at pericentric heterochromatin. Both events are under the control of Heat Shock Factor I (HSF1). Here we show that under heat shock, HSF1 recruits major cellular acetyltransferases, GCN5, TIP60 and p300 to pericentric heterochromatin leading to a targeted hyperacetylation of pericentric chromatin. Redistribution of histone acetylation toward pericentric region in turn directs the recruitment of Bromodomain and Extra-Terminal (BET) proteins BRD2, BRD3, BRD4, which are required for satellite III transcription by RNAP II. Altogether we uncover here a critical role for HSF1 in stressed cells relying on the restricted use of histone acetylation signaling over pericentric heterochromatin (HC).

Dynamics of the full length and mutated heat shock factor 1 in human cells.

Heat shock factor 1 is the key transcription factor of the heat shock response. Its function is to protect the cell against the deleterious effects of stress. Upon stress, HSF1 binds to and transcribes hsp genes and repeated satellite III (sat III) sequences present at the 9q12 locus. HSF1 binding to pericentric sat III sequences forms structures known as nuclear stress bodies (nSBs). nSBs represent a natural amplification of RNA pol II dependent transcription sites. Dynamics of HSF1 and of deletion mutants were studied in living cells using multi-confocal Fluorescence Correlation Spectroscopy (mFCS) and Fluorescence Recovery After Photobleaching (FRAP). In this paper, we show that HSF1 dynamics modifications upon heat shock result from both formation of high molecular weight complexes and increased HSF1 interactions with chromatin. These interactions involve both DNA binding with Heat Shock Element (HSE) and sat III sequences and a more transient sequence-independent binding likely corresponding to a search for more specific targets. We find that the trimerization domain is required for low affinity interactions with chromatin while the DNA binding domain is required for site-specific interactions of HSF1 with DNA.

Heat-shock factor 1 controls genome-wide acetylation in heat-shocked cells.

A major regulatory function has been evidenced here for HSF1, the key transcription factor of the heat-shock response, in a large-scale remodeling of the cell epigenome. Indeed, upon heat shock, HSF1, in addition to its well-known transactivating activities, mediates a genome-wide and massive histone deacetylation. Investigating the underlying mechanisms, we show that HSF1 specifically associates with and uses HDAC1 and HDAC2 to trigger this heat-shock-dependent histone deacetylation. This work therefore identifies HSF1 as a master regulator of global chromatin acetylation and reveals a cross-talk between HSF1 and histone deacetylases in the general control of genome organization in response to heat shock.

HIV-1 Tat targets Tip60 to impair the apoptotic cell response to genotoxic stresses.

HIV-1 transactivator Tat uses cellular acetylation signalling by targeting several cellular histone acetyltransferases (HAT) to optimize its various functions. Although Tip60 was the first HAT identified to interact with Tat, the biological significance of this interaction has remained obscure. We had previously shown that Tat represses Tip60 HAT activity. Here, a new mechanism of Tip60 neutralization by Tat is described, where Tip60 is identified as a substrate for the newly reported p300/CBP-associated E4-type ubiquitin-ligase activity, and Tat uses this mechanism to induce the polyubiquitination and degradation of Tip60. Tip60 targeting by Tat results in a dramatic impairment of the Tip60-dependent apoptotic cell response to DNA damage. These data reveal yet unknown strategies developed by HIV-1 to increase cell resistance to genotoxic stresses and show a role of Tat as a modulator of cellular protein ubiquitination.

The viral control of cellular acetylation signaling.

It is becoming clear that the post-translational modification of histone and non-histone proteins by acetylation is part of an important cellular signaling process controlling a wide variety of functions in both the nucleus and the cytoplasm. Recent investigations designate this signaling pathway as one of the primary targets of viral proteins after infection. Indeed, specific viral proteins have acquired the capacity to interact with cellular acetyltransferases (HATs) and deacetylases (HDACs) and consequently to disrupt normal acetylation signaling pathways, thereby affecting viral and cellular gene expression. Here we review the targeting of cellular HATs and HDACs by viral proteins and highlight different strategies adopted by viruses to control cellular acetylation signaling and to accomplish their life cycle.

Tat-controlled protein acetylation.

Human immunodeficiency virus, type 1-encoded transactivator protein Tat is known to be a substrate of and to interact with several nuclear histone acetyltransferases (HATs). Here we show that Tat is a general inhibitor of histone acetylation by cellular HATs and that for at least one of them, the CREB-binding protein (CBP), it induces a substrate selectivity. Indeed, in the presence of Tat, the acetylation of histones by CBP was severely inhibited, while that of p53 and MyoD remained unaffected. The C-terminal domain of Tat, dispensable for the activation of viral transcription, was found to be necessary and sufficient to interfere with histone acetylation. These results demonstrate that Tat is able to selectively modulate cellular protein acetylation by nuclear HATs and therefore to take over this specific signaling system in cells.

Cdyl: a new transcriptional co-repressor.

Cdyl (chromodomain-Y-like) is a chromodomain-containing protein that is predominantly expressed during mouse spermiogenesis. In its carboxy-terminal portion, there is a domain with homology to the coenzyme A (CoA) pocket of the enoyl-CoA hydratase/isomerase, which is shown here to be able to bind CoA and histone deacetylases (HDACs). It also efficiently represses transcription. Moreover, the binding of Hdac1 represses the ability of Cdyl to bind CoA, and a Cdyl-CoA interaction only occurs in the absence of HDACs. These data suggest that Cdyl is primarily a transcriptional co-repressor. However, the degradation of cellular Hdac1 and Hdac2, as observed here in the elongating spermatids, may provide an HDAC-free environment in which Cdyl could bind CoA and participate in the global chromatin remodelling that occurs in these cells.