Biology subjects

Pirot, N.

Publications and source records attributed to Pirot, N..

8 recordsLinked to original sources

bioRxiv2026

THE MULTIFUNCTIONAL PROTEIN E4F1 REGULATES MELANOCYTIC FUNCTIONS IN MICE THROUGH PROTEIN TRANSLATION AND MITF EXPRESSION

The multifunctional protein E4 transcription factor 1 (E4F1) is an essential regulator of skin homeostasis, playing a critical role in epidermal stem cell maintenance and keratinocyte differentiation. However, the functions of E4F1 in other skin cell type remain poorly investigated. Here, we describe its role in melanogenesis, the physiological process for synthesis of melanin pigments. Using genetically engineered mouse models that enabled conditional inactivation of E4f1 specifically in melanocytes, we demonstrated that E4f1 loss induces severe pigmentation defects without affecting melanocyte survival nor differentiation. At the molecular level, E4f1 depletion reduces the expression of its direct transcriptional target genes involved in protein translation, including Elp3 and Eef1g, leading to translation alterations and consequently the induction of the Integrated Stress Response (ISR). This response resulted in microphthalmia-associated transcription factor (MITF) downregulation, inducing a decrease in the expression of enzymes involved in melanin synthesis. Consistent with these findings, Elp3 or Eef1g depletion recapitulated the decrease in MITF levels in vitro, and pharmacological inhibition of ISR partially rescued melanin content in vivo, confirming a key role of the E4F1-protein translation-ISR cascade in melanogenesis. Together, our data identify E4F1-associated translation functions as a key regulator of the melanocytic lineage.

physiology↗

bioRxiv2023

RIP140 regulates HES1 oscillatory expression and mitogenic activity in colon cancer cells

BackgroundThe transcription factor RIP140 (Receptor Interacting Protein of 140 kDa) regulates intestinal homeostasis and tumorigenesis through the Wnt signaling. In this study, we have investigated its effect on the Notch/HES1 signaling pathway. MethodsThe impact on HES1 expression and activity was evaluated in colorectal cancer (CRC) cell lines and in transgenic mice, invalidated or not for the Rip140 gene in the intestinal epithelium. A tumor microarray and transcriptomic data sets were used to investigate RIP140 and HES1 expression in relation with patient survival. Statistical comparisons were performed with Mann-Whitney or Kruskal-Wallis or Chi2 tests. ResultsIn CRC cells, RIP140 positively regulated HES1 gene expression at the transcriptional level via an RBPJ/NICD-mediated mechanism. In support of these in vitro data, RIP140 and HES1 expression significantly correlated in mouse intestine and in a cohort of CRC samples, analyzed by immunohistochemistry, thus supporting the positive regulation of HES1 gene expression by RIP140. Interestingly, when the Notch pathway is fully activated, RIP140 exerted a strong inhibition of HES1 gene transcription controlled by the level of HES1 itself. Moreover, RIP140 directly interacts with HES1 and reversed its mitogenic activity in human CRC cells. In line with this observation, HES1 levels were associated with a better patient survival only when tumors expressed high levels of RIP140. ConclusionsOur data identify RIP140 as a key regulator of the Notch/HES1 signaling pathway with a dual effect on HES1 gene expression at the transcriptional level and a strong impact on colon cancer cell proliferation.

cancer biology↗

bioRxiv2022

E4F1 COORDINATES PYRUVATE METABOLISM AND THE ACTIVITY OF THE ELONGATOR COMPLEX TO ENSURE PROTEIN TRANSLATION FIDELITY DURING NEURONAL DEVELOPMENT

Pyruvate metabolism defects lead to severe neuropathies such as the Leigh syndrome (LS) but the molecular mechanisms underlying neuronal cell death remain poorly understood. Here, we unravel a connection between pyruvate metabolism and the regulation of the epitranscriptome that is relevant to LS pathogenesis. We identified the transcription factor E4F1 as a key coordinator of AcetylCoenzyme A (AcCoA) production by the pyruvate dehydrogenase complex (PDC) and its utilization as an essential co-factor by the Elongator complex to acetylate tRNAs at the wobble position uridine 34 (U34). E4F1-mediated direct transcriptional regulation of Dlat and Elp3, two genes encoding key subunits of the PDC and of the Elongator complex, respectively, ensured proper translation fidelity and cell survival in the central nervous system (CNS) during mouse embryonic development. Furthermore, analysis of PDH-deficient cells highlighted a crosstalk linking the PDC to ELP3 expression that is perturbed in LS patients.

developmental biology↗

bioRxiv2022

Three-dimensional imaging of vascular development in the mouse epididymis: a prerequisite to better understand the post-testicular immune context of spermatozoa

Long considered an accessory tubule of the male reproductive system, the epididymis is proving to be a key determinant of male fertility. In addition to its secretory role in ensuring functional maturation and survival of spermatozoa, the epididymis has a complex immune function. Indeed, it must manage both peripheral tolerance to sperm antigens foreign to the immune system and the protection of spermatozoa as well as the organ itself against pathogens ascending the epididymal tubule. Although our knowledge of the immunobiology of this organ is beginning to accumulate at the molecular and cellular levels, the organization of blood and lymphatic networks of this tissue, important players in the immune response, remains largely unknown. In the present report, we have taken advantage of a VEGFR3:YFP transgenic mouse model. Using high-resolution three-dimensional (3D) imaging and organ clearing coupled with multiplex immunodetections of lymphatic (LYVE1, PDPN, PROX1) and/or blood (PLVAP/Meca32) markers, we provide for the first time a simultaneous deep 3D view of the lymphatic and blood epididymal vasculature in the mature adult mouse as well as during postnatal development. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC="FIGDIR/small/505406v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@307802org.highwire.dtl.DTLVardef@170c07org.highwire.dtl.DTLVardef@116b006org.highwire.dtl.DTLVardef@7e7f66_HPS_FORMAT_FIGEXP M_FIG Summary of the expansion of the conventional and hybrid lymphatic vasculature during postnatal development of the murine epididymis. C_FIG

developmental biology↗

bioRxiv2022

CDK8 and CDK19 act redundantly to control the CFTR pathway in the intestinal epithelium

CDK8 and CDK19 form a conserved cyclin-dependent kinase subfamily that interacts with the essential transcription complex, Mediator, and also promotes transcription by phosphorylating the C-terminal domain (CTD) of RNA polymerase II. Cells lacking either CDK8 or CDK19 are viable and have limited transcriptional alterations, but whether the two kinases redundantly control cell differentiation is unknown. Here, we find that CDK8 is dispensable for RNA polII CTD phosphorylation, regulation of gene expression, normal intestinal homeostasis and efficient tumourigenesis in mice. Furthermore, CDK8 is largely redundant with CDK19 in the control of gene expression. Yet, while their combined deletion in intestinal organoids reduces long-term proliferative capacity, it is not lethal and allows differentiation. Nevertheless, in double mutant organoids, the cystic fibrosis transmembrane conductance regulator (CFTR) pathway is transcriptionally and functionally downregulated, leading to mucus accumulation and increased secretion by goblet cells. This phenotype can be recapitulated by pharmacological inhibition of CDK8/19 kinase activity. Thus, the Mediator kinases are not essential for cell proliferation and differentiation, but they cooperate to regulate tissue-specific transcriptional programmes.

cell biology↗

bioRxiv2020

In Lyl1-/- mice, adipose stem cell vascular niche impairment leads to premature development of fat tissues

Lymphoblastic leukemia-derived sequence 1 (Lyl1) encodes a hematopoietic- and endothelial-specific transcriptional factor. Lyl1-deficient mice are viable, but they display mild hematopoietic and vascular defects. Here, we report that young Lyl1-/- mice exhibit transient obesity associated with general expansion of adipose tissues and unrelated to food intake. The increased fat tissue development in Lyl1-/- mice resulted from an earlier adipocyte differentiation of adipose stem cells (ASCs) through non-cell autonomous mechanisms. Specifically, we found that in Lyl1-/- mice, the vascular structures of adipose tissues are unstable, more prone to angiogenesis and, consequently, cannot maintain adipose progenitors in the niche vessel wall. Together, our data show that in Lyl1-/- mice, the impaired vascular compartment of the adipose niche promotes uncontrolled ASC activation and differentiation, leading to early adipocyte expansion and premature depletion of ASCs. Our study highlights the major structural role of the adipose tissue vascular niche in coordinating stem cell self-renewal and differentiation into adipocytes.

physiology↗

bioRxiv2019

Ki-67 supports global gene expression programmes driving tumourigenesis

Recent studies have shown that the cell proliferation antigen Ki-67 is not required for cell proliferation. Here, we demonstrate that Ki-67 enables implementation of transcriptional programmes conferring cellular plasticity, and is required for each step of tumour initiation, growth and metastasis. Ki-67 knockout causes global transcriptome remodelling, which, in mammary carcinoma cells, inhibits the epithelial-mesenchymal transition in a polycomb-repressive complex 2-dependent manner. This results in suppression of stem cell characteristics and sensitisation to various drug classes. Cancer cells lacking Ki-67 proliferate normally in vivo, but tumour growth is inhibited due to disrupted angiogenesis, and metastasis is abrogated. Finally, mice lacking Ki-67 are resistant to chemical or genetic induction of intestinal tumourigenesis. Thus, Ki-67, which is expressed in all proliferating cancer cells, confers the plasticity required for different steps of carcinogenesis.

cancer biology↗

bioRxiv2018

The mouse HP1 proteins are not required for cell viability but are essential for preventing liver tumorigenesis

Chromatin organization plays essential roles in cell identity and functions. Here, we demonstrated by hepatocyte-specific inactivation of the genes encoding the three Heterochromatin Protein 1 (HP1, {beta} and {gamma}) in mice (HP1-TKO) that these proteins are dispensable for hepatocyte activity and survival. Conversely, the chronic absence of these proteins led to a drastic increased incidence of liver tumor development. Molecular characterization of HP1-TKO hepatocytes revealed that HP1 proteins are required for maintenance of histone marks associated with heterochromatin, and for the appropriate expression of large number of genes involved in liver-specific functions as well as in genes encoding for transcriptional repressors of the KRAB-ZFP family. Moreover, several specific endogenous retrovirus families were upregulated in HP1-TKO hepatocytes, leading to the deregulated expression of genes in their vicinity. Our findings indicate that HP1 proteins act as guardians of liver homeostasis to prevent tumor development through the modulation of multiple chromatin-associated events.

cancer biology↗