RESUMO
PML/RARA, a potent transcriptional inhibitor of nuclear receptor signaling, represses myeloid differentiation genes and drives acute promyelocytic leukemia (APL). Association of the retinoid X receptor-α (RXRA) coreceptor to PML/RARA is required for transformation, with RXRA promoting its efficient DNA binding. APL is exquisitely sensitive to retinoic acid (RA) and arsenic trioxide (arsenic), which both trigger cell differentiation in vivo. Whereas RA elicits transcriptional activation of PML/RARA targets, how arsenic triggers differentiation remains unclear. Here we demonstrate that extinction of PML/RARA triggers terminal differentiation in vivo. Similarly, ablation of retinoid X receptors loosens PML/RARA DNA binding, inducing terminal differentiation of APL cells ex vivo or in vivo. RXRA sumoylation directly contributes to PML/RARA-dependent transformation ex vivo, presumably by enhancing transcriptional repression. Thus, APL differentiation is a default program triggered by clearance of PML/RARA-bound promoters, rather than obligatory active transcriptional activation, explaining how arsenic elicits APL maturation through PML/RARA degradation.
Assuntos
Diferenciação Celular/genética , Leucemia Promielocítica Aguda/genética , Proteínas de Fusão Oncogênica/genética , Regiões Promotoras Genéticas/genética , Animais , Antineoplásicos/farmacologia , Trióxido de Arsênio , Arsenicais/farmacologia , Células COS , Linhagem Celular Tumoral , Transformação Celular Neoplásica/genética , Células Cultivadas , Chlorocebus aethiops , Perfilação da Expressão Gênica , Humanos , Leucemia Promielocítica Aguda/metabolismo , Leucemia Promielocítica Aguda/patologia , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos , Camundongos Nus , Camundongos Transgênicos , Proteínas de Fusão Oncogênica/metabolismo , Óxidos/farmacologia , Ligação Proteica , Interferência de RNA , Receptor X Retinoide alfa/genética , Receptor X Retinoide alfa/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sumoilação , Ativação Transcricional/genética , Tretinoína/farmacologiaRESUMO
BACKGROUND: Academic-sponsored trials for rare diseases face many challenges; the present paper identifies hurdles in the set-up of six multinational clinical trials for drug repurposing, as use cases. METHODS: Six academic-sponsored multinational trials aiming to generate knowledge on rare diseases drug repurposing were used as examples to identify problems in their set-up. Coordinating investigators leading these trials provided feedback on hurdles linked to study, country, and site set up, on the basis of pre-identified categories established through the analysis of previous peer-reviewed publications. RESULTS: Administrative burden and lack of harmonization for trial-site agreements were deemed as a major hurdle. Other main identified obstacles included the following: (1) complexity and restriction on the use of public funding, especially in a multinational set up, (2) drug supply, including procurement tendering rules and country-specific requirements for drug stability, and (3) lack of harmonization on regulatory requirements to get trial approvals. CONCLUSION: A better knowledge of the non-commercial clinical research landscape and its challenges and requirements is needed to make drugs-especially those with less commercial gain-accessible to rare diseases patients. Better information about existing resources like research infrastructures, clinical research programs, and counseling mechanisms is needed to support and guide clinicians through the many challenges associated to the set-up of academic-sponsored multinational trials.
Assuntos
Reposicionamento de Medicamentos , Doenças Raras , Ensaios Clínicos como Assunto , Humanos , Organizações , Doenças Raras/diagnóstico , Doenças Raras/tratamento farmacológicoRESUMO
Acute promyelocytic leukaemia (APL) is induced by fusion proteins always implying the retinoic acid receptor RARa. Although PML-RARa and other fusion oncoproteins are able to bind DNA as homodimers, in vivo they are always found in association with the nuclear receptor RXRa (Retinoid X Receptor). Thus, RXRa is an essential cofactor of the fusion protein for the transformation. Actually, RXRa contributes to several aspects of in vivo -transformation: RARa fusion:RXRa hetero-oligomeric complexes bind DNA with a much greater affinity than RARa fusion homodimers. Besides, PML-RARa:RXRa recognizes an enlarged repertoire of DNA binding sites. Thus the association between fusion proteins and RXRa regulates more genes than the homodimer alone. Titration of RXRa by the fusion protein may also play a role in the transformation process, as well as post-translational modifications of RXRa in the complex. Finally, RXRa is required for rexinoid-induced APL differentiation. Thus, RXRa is a key member of the oncogenic complex.