RESUMO
ΔNp63α, implicated as an oncogene, is upregulated by activated Akt, part of a well-known cell survival pathway. Inhibition of Akt activation by phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and the presence of putative p63-binding sites in the pten promoter led us to investigate whether ΔNp63α regulates PTEN expression. Knockdown of ΔNp63α led to increases in PTEN levels and loss of activated Akt, while overexpression of ΔNp63α decreased PTEN levels and elevated active Akt. The repression of PTEN by ΔNp63α occurs independently of p53 status, as loss of ΔNp63α increases PTEN expression in cell lines with and without functional p53. In addition, decreased levels of ΔNp63α resulted in an increase in nuclear PTEN. Conversely, in vivo nuclear PTEN was absent in the proliferative basal layer of the epidermis where ΔNp63α expression is highest. Additionally, we show that in keratinocytes a balance between ΔNp63α and PTEN regulates Akt activation and maintains normal proliferation rates. This balance is disrupted in non-melanoma skin cancers through increased ΔNp63α levels, and could enhance proliferation and subsequent neoplastic development. Our studies show that ΔNp63α negatively regulates PTEN, thereby providing a feedback loop between PTEN, Akt and ΔNp63α, which has an integral role in skin cancer development.
Assuntos
Proliferação de Células , Queratinócitos/fisiologia , PTEN Fosfo-Hidrolase/metabolismo , Transporte Proteico , Fatores de Transcrição/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Animais , Sequência de Bases , Carcinoma Basocelular/metabolismo , Carcinoma Basocelular/patologia , Carcinoma de Células Escamosas/metabolismo , Carcinoma de Células Escamosas/patologia , Núcleo Celular/metabolismo , Células Cultivadas , Regulação para Baixo , Ativação Enzimática , Retroalimentação Fisiológica , Expressão Gênica , Regulação da Expressão Gênica , Humanos , Queratinócitos/metabolismo , Camundongos , Dados de Sequência Molecular , PTEN Fosfo-Hidrolase/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Elementos de Resposta , Pele/metabolismo , Neoplasias Cutâneas/metabolismo , Neoplasias Cutâneas/patologiaRESUMO
The secosteroid hormone vitamin D3 (VD3) exerts its biological actions through its cognate receptor, the vitamin D receptor (VDR). Vitamin D3 and VDR have a key function in bone formation and keratinocyte differentiation, exert antiproliferative actions in human cancer, and is widely used as a chemotherapeutic agent for cancer. In addition, VD3 promotes differentiation of human osteosarcoma cells by up-regulating genes involved in cell cycle arrest and osteoblastic differentiation. Although considerable work has been carried out in understanding the molecular mechanisms underlying the VD3-mediated differentiation of human osteosarcoma cells, the upstream regulation of VD3 signaling pathway is still unclear. In this study, we show that p73 acts as an upstream regulator of VD3-mediated osteoblastic differentiation. Transcription factor p73, a p53 homolog, has been shown to have a function in development and recently been termed as a tumor suppressor. Silencing p73 results in a significant reduction of VD3-mediated osteoblastic differentiation; although DNA damage induced p73 leads to an increase in VD3-mediated differentiation of osteosarcoma cells. Together, our data implicate a novel function for p73 in vitamin D-mediated differentiation of human osteosarcoma cells.
Assuntos
Diferenciação Celular , Proteínas de Ligação a DNA/metabolismo , Proteínas Nucleares/metabolismo , Osteoblastos/efeitos dos fármacos , Osteoblastos/fisiologia , Proteínas Supressoras de Tumor/metabolismo , Vitamina D/farmacologia , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/fisiologia , Linhagem Celular Tumoral , Dano ao DNA , Proteínas de Ligação a DNA/genética , Humanos , Proteínas Nucleares/genética , Osteoblastos/citologia , Osteocalcina/genética , Osteocalcina/metabolismo , Osteopontina/genética , Osteopontina/metabolismo , Osteossarcoma/genética , Osteossarcoma/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Receptores de Calcitriol/genética , Receptores de Calcitriol/metabolismo , Transdução de Sinais/fisiologia , Proteína Tumoral p73 , Proteínas Supressoras de Tumor/genéticaRESUMO
p63, a p53 homolog has been shown to play a role in development and cancer. p63 is essential for both commitment of ectoderm to stratified epithelia and for the proliferative potential of epithelial stem cells. p63 knockout mice are born with severe development defects and lack organs of epithelial origin. In addition, p63 has also been shown to play a role in cancer development through the differential regulation of genes with tumor suppressor function and genes involved in metastasis. In order to understand the role of p63 in cancer and development, genes that are specifically regulated by p63 but not p53 were identified. In this study, we provide evidence that p63gamma specifically upregulates vitamin D Receptor (VDR). In contrast, p53 does not appear to be involved in upregulation of VDR expression. Additionally, we demonstrate that a naturally occurring p63 missense mutant, p63gamma (R279H) and p14(ARF), both act in a dominant negative manner to inhibit p63gamma-mediated upregulation of VDR. Furthermore, using chromatin immunoprecipitation assays, we demonstrated that p63 directly binds to the VDR promoter in vivo. Our findings clearly demonstrate that VDR is a direct target of p63 and suggests that p63 may play a role in cancer and differentiation through modulation of the VDR pathway.
