Thèse la Citrullination de l'Arn Polymérase Ii Comme Régulateur du Contrôle Transcriptionnel dans le Cancer du Sein Triple Négatif H/F Doctorat.Gouv.Fr

Candidat très motivé possédant une solide expérience en recherche sur le cancer, en biologie cellulaire et en biologie moléculaire

Application link : https://edd-projets.utoulouse.fr/

Établissement : Université de Toulouse École doctorale : BSB - Biologie, Santé, Biotechnologies Laboratoire de recherche : IPBS - Institut de Pharmacologie et Biologie Structurale Direction de la thèse : Priyanka SHARMA ORCID 0000000338903590 Début de la thèse : 2027-10-01 Date limite de candidature : 2026-11-23T23:59:59 La progression du cancer est pilotée par des programmes transcriptionnels régulés non seulement par des facteurs de transcription, mais aussi par des modifications post-traductionnelles (MPT), qui modulent finement la fonction des protéines et la signalisation cellulaire. Parmi ces MPT, la citrullination des protéines s'est révélée être une MPT régulatrice importante impliquée dans l'oncogenèse. La citrullination est la conversion enzymatique de la peptidyl-arginine en peptidyl-citrulline, catalysée par la famille d'enzymes peptidyl arginine désiminases (PADI). Cette modification augmente l'hydrophobicité des protéines et altère leur conformation, affectant ainsi la formation de liaisons hydrogène, la structure protéique, les interactions protéine-protéine et les interactions protéine-acide nucléique (1-4). Par conséquent, la citrullination est impliquée dans la régulation des interactions histone-ADN, l'expression des gènes et l'agrégation des protéines (1,5-9), suggérant un rôle étendu dans le contrôle de processus cellulaires essentiels. Parmi les membres de la famille PADI, PADI2 est l'enzyme la plus fréquemment surexprimée dans plusieurs types de tumeurs, notamment le cancer du sein (2, 10-15). Nos études récentes ont identifié la citrullination de l'arginine 1810 (Cit1810) de l'ARN polymérase II (RNAPII), catalysée par PADI2, comme un régulateur essentiel de la transcription et de la prolifération cellulaire dans les cellules cancéreuses du sein (2, 4, 16-17). De plus, notre analyse récente a mis en évidence une association entre une expression élevée de PADI2 et les formes agressives du cancer du sein, soulignant ainsi le rôle potentiel de la citrullination de la RNAPII par PADI2 comme mécanisme sous-estimé par lequel les cellules TNBC pourraient exploiter l'appareil transcriptionnel pour maintenir des états transcriptionnels malins. Forts de ces observations, nous proposons un programme de doctorat multidisciplinaire. Ce projet, codirigé par le Dr Priyanka Sharma (Équipe Mécanismes épigénétiques du cancer, IPBS, Toulouse, France) et le Dr Juan Torreño Piña (Équipe Nano-imagerie de molécules uniques des glycoprocessus membranaires cellulaires, Centre national de biotechnologie, CSIC, Madrid, Espagne), vise à élucider les mécanismes moléculaires par lesquels Cit1810-RNAPII, via PADI2, régule la transcription et à évaluer sa pertinence clinique dans des échantillons de patientes atteintes d'un cancer du sein triple négatif (TNBC). Ces études apporteront des connaissances fondamentales sur la régulation transcriptionnelle dans les cancers du sein agressifs et pourraient ouvrir la voie à de nouvelles pistes thérapeutiques pour le traitement du TNBC. Triple-negative breast cancer (TNBC) accounts for approximately 15% of all breast cancer cases, representing nearly 300,000 new diagnoses worldwide each year ( ~9,000 cases annually in France), and globally, it causes ~500 deaths daily (18-20). Defined by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression, TNBC is one of the most aggressive breast cancer subtypes. Unlike other breast cancer forms, TNBC patients do not benefit from endocrine or HER2-targeted therapies. Although chemotherapy, immunotherapy, and poly(ADP-ribose) polymerase (PARP) inhibitors have improved outcomes in selected patient populations, treatment resistance, disease recurrence, and metastatic progression remain major clinical challenges (18-20). Consequently, the identification of novel mechanism-based therapeutic vulnerabilities is an urgent unmet need.
Transcriptional dysregulation is a hallmark of TNBC and plays a central role in maintaining oncogenic gene expression programs that drive tumor initiation, progression, and therapeutic resistance (21-22). In this context, we have focused on protein citrullination, an emerging post-translational modification (PTM) with important regulatory functions. Citrullination, also known as deimination, is the calcium-dependent enzymatic conversion of peptidyl-arginine into peptidyl-citrulline, catalyzed by members of the peptidyl arginine deiminase (PADI) enzyme family (1,2). This modification results in the loss of a positive charge and alters protein hydrophobicity and conformation, thereby influencing hydrogen bonding, protein structure, protein-protein interactions, and protein-nucleic acid interactions (1-4). Given the fundamental importance of these molecular interactions, citrullination has the potential to regulate diverse cellular processes involved in cancer development and therapy resistance. Indeed, citrullination of core histones has been implicated in the regulation of transcription, DNA damage responses, and cellular pluripotency (6-14), highlighting its broader role in controlling key physiological and pathological processes.
Among the five members of the PADI family, PADI2 is the most evolutionarily conserved and broadly expressed isoform (2,3). Elevated PADI2 expression has been linked to multiple pathological conditions, including autoimmune and neurological disorders, as well as several malignancies such as breast and ovarian cancers (2,7-11). Importantly, accumulating evidence indicates that PADI2 contributes to tumor progression and the acquisition of therapeutic resistance (2,12-13). However, the molecular mechanisms through which PADI2-mediated citrullination regulates cellular functions and promotes cancer progression remain incompletely understood.
Notably, PADI2 is the only PADI family member known to catalyze the citrullination of arginine 1810 (R1810) within the carboxyl-terminal domain (CTD) of RNA polymerase II (RNAPII), generating the Cit1810-RNAPII modification (16,17). This unique PTM facilitates transcription elongation by enhancing the interaction of RNAPII with the positive transcription elongation factor b (P-TEFb) complex, thereby promoting the expression of genes involved in cell proliferation and tumor growth (4,16,17). Our analyses further demonstrate that elevated PADI2 expression is strongly associated with aggressive breast cancer phenotypes. Together, these findings identify PADI2-mediated RNAPII citrullination as a previously underappreciated mechanism through which TNBC cells may exploit the transcriptional machinery to sustain oncogenic transcriptional programs. Collectively, these observations provide a compelling rationale to investigate the molecular mechanisms governing the PADI2-Cit1810-RNAPII axis in TNBC.
Considering the regulatory role of Cit1810-RNAPII and its functional impact on cancer progression (16,17), we proposed to investigate the potential molecular mechanisms by which Cit1810-RNAPII impacts the RNAPII dynamics in transcription machinery in TNBC cells. Therefore, we proposed to analyze the impact of Cit1810-RNAPII on the spatio-temporal organization of chromatin in live cells using single-particle tracking experiments. Indeed, this raises an intriguing question in the field to investigate the molecular mechanism by which Cit1810-RNAPII could tether with the transcriptional proteins to fine-tune the gene regulation in TNBC cells. Therefore, it is critical to analyze Cit1810-RNAPII interaction with the essential transcriptional proteins to get mechanistic insights regarding the profound impact of Cit1810-RNAPII on transcription machinery. We expect this work to unveil a key regulatory function of Cit1810-RNAPII in the transcriptional landscape in TNBC cells. Furthermore, we planned to confirm the clinical significance of Cit1810-RNAPII mark in TNBC patients, and hence, we aim to perform Cit1810-RNAPII level using immunohistochemistry in TNBC and non-TNBC patient samples. We envisage that this knowledge will be useful to provide the association of Cit1810-RNAPII with clinopathologcal features and also assess if Cit1810-RNAPII could be a predictive marker for a specific subset of TNBC patients.