RESUMO
The presence of hypoxic regions in solid tumors is an adverse prognostic factor for patient outcome. Here, we show that hypoxia induces the expression of Ephrin-A3 through a novel hypoxia-inducible factor (HIF)-mediated mechanism. In response to hypoxia, the coding EFNA3 mRNA levels remained relatively stable, but HIFs drove the expression of previously unknown long noncoding (lnc) RNAs from EFNA3 locus and these lncRNA caused Ephrin-A3 protein accumulation. Ephrins are cell surface proteins that regulate diverse biological processes by modulating cellular adhesion and repulsion. Mounting evidence implicates deregulated ephrin function in multiple aspects of tumor biology. We demonstrate that sustained expression of both Ephrin-A3 and novel EFNA3 lncRNAs increased the metastatic potential of human breast cancer cells, possibly by increasing the ability of tumor cells to extravasate from the blood vessels into surrounding tissue. In agreement, we found a strong correlation between high EFNA3 expression and shorter metastasis-free survival in breast cancer patients. Taken together, our results suggest that hypoxia could contribute to metastatic spread of breast cancer via HIF-mediated induction of EFNA3 lncRNAs and subsequent Ephrin-A3 protein accumulation.
Assuntos
Neoplasias da Mama/metabolismo , Loci Gênicos , Fator 1 Induzível por Hipóxia/metabolismo , Proteínas de Neoplasias/metabolismo , RNA Longo não Codificante/biossíntese , RNA Neoplásico/biossíntese , Animais , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Hipóxia Celular/genética , Linhagem Celular Tumoral , Efrina-A3/genética , Efrina-A3/metabolismo , Feminino , Células Endoteliais da Veia Umbilical Humana , Humanos , Fator 1 Induzível por Hipóxia/genética , Camundongos , Camundongos Nus , Metástase Neoplásica , Proteínas de Neoplasias/genética , RNA Longo não Codificante/genética , RNA Neoplásico/genética , Peixe-ZebraRESUMO
The ascomycete Fusarium fujikuroi produces carotenoids by means of the enzymes encoded by three car genes. The enzymes encoded by carRA and carB are responsible of the synthesis of beta-carotene and torulene, respectively, while the product encoded by carT cleaves torulene to produce the acidic xanthophyll neurosporaxanthin. carRA and carB are found in a cluster with a third gene, carO, which codes for an opsin-like protein. However, no information is available on the sequence or chromosomal location of carT, which has been identified only by mutant analysis. Transcription of the three clustered genes is stimulated by light and by mutations in a regulatory gene, leading to overproduction of carotenoids. We have now identified a fourth gene in the car cluster, called carX, which codes for a protein similar to known carotenoid-cleaving oxygenases. carX is transcribed divergently from carRA, and exhibits the same transcriptional pattern as carRA, carB and carO. Targeted deletion of carX resulted in a phenotype characterized by a significant increase in the overall carotenoid content. In the dark, the carX mutants accumulate at least five times more carotenoids than the wild type, and exhibit partial derepression of carRA and carB transcription. The mutants also show more intense pigmentation in the light, but the increase in the carotenoid content relative to the wild type is less than twofold. Under these conditions, the mutants also show a relative increase in the amounts of phytoene and cyclic carotenoids formed, suggesting that CarRA activity is enhanced.
