RESUMO
In this study, several cancer-related proteins (Bax, p300, E2F4 and securin) have been proven to be substrates of ubiquitin-specific peptidase 24 (USP24), and relevance has been shown between USP24 and its substrates in samples from clinical lung cancer patients. Silencing USP24 increases the cancer formation by inhibiting cellular apoptosis and increasing cellular proliferation. Epidermal growth factor (EGF) treatment, and the KrasG12D and EGFRL858R mutations decrease USP24 protein stability via EGF- or CDK1-mediated phosphorylation at Ser1616, Ser2047 and Ser2604. Knockdown of USP24 decreases Bax and p300 levels, and reduces Ku70 acetylation, thereby preventing cancer cell apoptosis. In addition, knockdown of USP24 increases cell cycle progression by enhancing the G1-S transition and metaphase-anaphase transition. The molecular mechanism involves a decrease in the USP24 level, which reduces the expression of E2F4 and its partner TFDP1, and thus increases the G1/S transition. In conclusion, the USP24 level was decreased during the early stage of cancer and the mitotic stage of the cell cycle to regulate its substrates p300, Bax, E2F4 and securin, resulting in decreased cell apoptosis and increased cell cycle progression and, thus, cancer formation.
Assuntos
Carcinogênese/efeitos dos fármacos , Carcinogênese/genética , Fator de Crescimento Epidérmico/farmacologia , Ubiquitina Tiolesterase/genética , Células A549 , Animais , Ciclo Celular/genética , Linhagem Celular Tumoral , Proteína p300 Associada a E1A/genética , Fator de Transcrição E2F4/genética , Fator de Crescimento Epidérmico/fisiologia , Regulação Enzimológica da Expressão Gênica/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica , Células HeLa , Humanos , Camundongos , Camundongos Transgênicos , Securina/genética , Proteína X Associada a bcl-2/genéticaRESUMO
Ubiquitin is a critical modifier regulating the degradation and function of its target proteins during posttranslational modification. Here we found that ubiquitin-specific peptidase 24 (USP24) is highly expressed in cell lines with enhanced malignancy and in late-stage lung cancer clinical samples. Studying single-nucleotide polymorphisms (SNPs) of USP24 using genomic DNA of lung cancer patients revealed an increase in SNP 7656C/T. When using RNA specimens instead of the genomic DNA of lung cancer patients, we found significant increases in the ratios of variants 930C/T and 7656T/C, suggesting that variants at these two sites are not only caused by the SNP of DNA but also by the RNA editing. USP24-930T and USP24-7656C increase USP24 expression levels by increasing RNA stability. Knocking down USP24 increased Suv39h1 level through a decrease in mouse double-minute 2 homolog levels, thus enhancing lysine-9 methylation of histone H3, and resulting in the prevention of lung cancer malignancy. In conclusion, as USP24 variant analysis revealed a higher ratio of variants in blood specimens of lung cancer patients than that in normal individuals, USP24-930T and USP24-7656C might be useful as diagnostic markers for cancer detection.