RESUMO
Activation of oncogenes by mechanisms other than genetic aberrations such as mutations, translocations, or amplifications is largely undefined. Here we report a novel isoform of the anaplastic lymphoma kinase (ALK) that is expressed in â¼11% of melanomas and sporadically in other human cancer types, but not in normal tissues. The novel ALK transcript initiates from a de novo alternative transcription initiation (ATI) site in ALK intron 19, and was termed ALK(ATI). In ALK(ATI)-expressing tumours, the ATI site is enriched for H3K4me3 and RNA polymerase II, chromatin marks characteristic of active transcription initiation sites. ALK(ATI) is expressed from both ALK alleles, and no recurrent genetic aberrations are found at the ALK locus, indicating that the transcriptional activation is independent of genetic aberrations at the ALK locus. The ALK(ATI) transcript encodes three proteins with molecular weights of 61.1, 60.8 and 58.7 kilodaltons, consisting primarily of the intracellular tyrosine kinase domain. ALK(ATI) stimulates multiple oncogenic signalling pathways, drives growth-factor-independent cell proliferation in vitro, and promotes tumorigenesis in vivo in mouse models. ALK inhibitors can suppress the kinase activity of ALK(ATI), suggesting that patients with ALK(ATI)-expressing tumours may benefit from ALK inhibitors. Our findings suggest a novel mechanism of oncogene activation in cancer through de novo alternative transcription initiation.
Assuntos
Regulação Neoplásica da Expressão Gênica/genética , Neoplasias/enzimologia , Neoplasias/genética , Receptores Proteína Tirosina Quinases/genética , Iniciação da Transcrição Genética , Alelos , Quinase do Linfoma Anaplásico , Animais , Linhagem Celular Tumoral , Proliferação de Células , Transformação Celular Neoplásica , Feminino , Células HEK293 , Histonas/química , Histonas/metabolismo , Humanos , Íntrons/genética , Isoenzimas/antagonistas & inibidores , Isoenzimas/biossíntese , Isoenzimas/química , Isoenzimas/genética , Lisina/metabolismo , Metilação , Camundongos , Dados de Sequência Molecular , Peso Molecular , Células NIH 3T3 , Neoplasias/tratamento farmacológico , Oncogenes/genética , Estrutura Terciária de Proteína/genética , RNA Polimerase II/metabolismo , RNA Mensageiro/análise , RNA Mensageiro/genética , Receptores Proteína Tirosina Quinases/antagonistas & inibidores , Receptores Proteína Tirosina Quinases/biossíntese , Receptores Proteína Tirosina Quinases/química , Transdução de SinaisRESUMO
Prostate cancer exhibits a lineage-specific dependence on androgen signaling. Castration resistance involves reactivation of androgen signaling or activation of alternative lineage programs to bypass androgen requirement. We describe an aberrant gastrointestinal-lineage transcriptome expressed in â¼5% of primary prostate cancer that is characterized by abbreviated response to androgen-deprivation therapy and in â¼30% of castration-resistant prostate cancer. This program is governed by a transcriptional circuit consisting of HNF4G and HNF1A. Cistrome and chromatin analyses revealed that HNF4G is a pioneer factor that generates and maintains enhancer landscape at gastrointestinal-lineage genes, independent of androgen-receptor signaling. In HNF4G/HNF1A-double-negative prostate cancer, exogenous expression of HNF4G at physiologic levels recapitulates the gastrointestinal transcriptome, chromatin landscape, and leads to relative castration resistance.
Assuntos
Resistencia a Medicamentos Antineoplásicos/fisiologia , Regulação Neoplásica da Expressão Gênica/fisiologia , Fator 1-alfa Nuclear de Hepatócito/metabolismo , Fator 4 Nuclear de Hepatócito/metabolismo , Neoplasias de Próstata Resistentes à Castração/metabolismo , Animais , Xenoenxertos , Humanos , Masculino , Camundongos , Camundongos SCID , Neoplasias de Próstata Resistentes à Castração/patologia , Inibidor da Tripsina Pancreática de Kazal/biossínteseRESUMO
Fusion between TMPRSS2 and ERG, placing ERG under the control of the TMPRSS2 promoter, is the most frequent genetic alteration in prostate cancer, present in 40-50% of cases. The fusion event is an early, if not initiating, event in prostate cancer, implicating the TMPRSS2-positive prostate epithelial cell as the cancer cell of origin in fusion-positive prostate cancer. To introduce genetic alterations into Tmprss2-positive cells in mice in a temporal-specific manner, we generated a Tmprss2-CreERT2 knock-in mouse. We found robust tamoxifen-dependent Cre activation in the prostate luminal cells but not basal epithelial cells, as well as epithelial cells of the bladder and gastrointestinal (GI) tract. The knock-in allele on the Tmprss2 locus does not noticeably impact prostate, bladder, or gastrointestinal function. Deletion of Pten in Tmprss2-positive cells of adult mice generated neoplasia only in the prostate, while deletion of Apc in these cells generated neoplasia only in the GI tract. These results suggest that this new Tmprss2-CreERT2 mouse model will be a useful resource for genetic studies on prostate and colon.