RESUMO
The early genes E6 and E7 from human papillomaviruses (HPVs) play a key role in the development of cervical cancer. Modulation of E6 and E7 gene expression may alter tumour progression; therefore, modifiers of viral transcription such as hormones or growth factors are potential risk factors in cancer development. We have analysed the effects of epidermal growth factor (EGF) on E6/E7 mRNA from human papillomavirus type 16 (HPV-16) by Northern blot in two cell lines, SiHa cervical carcinoma cells, and HPK IA, an HPV-16-immortalized keratinocyte cell line. E6/E7 mRNA is EGF-inducible in SiHa cells, with the earliest response after 2 h. In contrast, in HPK IA cells no increase in E6/E7 RNA is observed, suggesting a differential EGF response of viral transcription in tumour cells compared with keratinocytes. We demonstrate that the cell type-specific HPV-16 enhancer is a target of EGF-induced signals, as its activity is amplified by EGF in SiHa cell transfections. However, when transfected into HPK IA keratinocytes, the viral enhancer shows no EGF response. The enhancer contains two binding sites for the transcription factor AP-1, a potential mediator of the EGF signalling cascade. Enhancer subfragments with single AP-1 binding sites are also EGF-responsive in SiHa cells. Mutating either AP-1 site in the complete enhancer decreases the EGF response, whereas a double mutation causes a complete loss of EGF regulation, suggesting that the EGF induction of HPV-16 early transcription requires AP-1 activation. We conclude that alterations of EGF responsiveness that increase viral oncogene expression may contribute to cervical cancer progression.
Assuntos
Elementos Facilitadores Genéticos/genética , Fator de Crescimento Epidérmico/farmacologia , Proteínas Oncogênicas Virais/genética , RNA Mensageiro/biossíntese , Proteínas Repressoras , Fator de Transcrição AP-1/metabolismo , Sequência de Bases , Linhagem Celular Transformada , DNA de Neoplasias/metabolismo , Progressão da Doença , Elementos Facilitadores Genéticos/efeitos dos fármacos , Feminino , Regulação Viral da Expressão Gênica , Humanos , Queratinócitos , Dados de Sequência Molecular , Mutação , Papillomaviridae/genética , Proteínas E7 de Papillomavirus , RNA Viral/biossíntese , Transdução de Sinais/genética , Transcrição Gênica/efeitos dos fármacos , Transcrição Gênica/genética , Transfecção , Células Tumorais Cultivadas , Neoplasias do Colo do ÚteroRESUMO
Cytokines are pleiotropic peptides produced by lymphoid cells that play important roles in cellular proliferation and multiplication. Diminished or enhanced production or constitutive secretion of cytokines contributes to the aetiology and pathogenesis of several diseases. They are soluble mediators eliciting specific responses of different target cells of paracrine, autocrine and cascade systems of the organism. Their secretion is regulated at the molecular genetic level. Gene rearrangements of cytokines and their receptors have been demonstrated in several diseases. As means of specific or supportive therapy, cytokine treatment has been used both in neoplastic and other proliferative diseases. Lymphokines and interferons comprise the first, whereas colony stimulating factors and growth factors yield the second group of cytokines. Most scientific experience is with interferon-alpha. Its anti-viral mechanism of action has been extensively studied and clarified, whereas its antitumour effect is more obscure and is a result of many simultaneous biologic events.
