Hypoxia activated long non-coding RNA HABON regulates the growth and proliferation of hepatocarcinoma cells by binding to and antagonizing HIF-1 alpha.

The adaptation of tumour cells to hypoxic microenvironment is one of the most significant characteristics of many malignant tumour diseases including hepatocarcinoma. Recently, long non-coding RNAs (lncRNAs) have been reported to play important roles in the various levels of gene regulation thus functioning in growth and survival of tumour cells. Here, new hypoxia-related lncRNAs in hepatocarcinoma cells were screened and validated by lncRNA chip-array as well as real-time RT-PCR. Among them, a hypoxia-activated lncRNA that we identified and termed Hypoxia-Activated BNIP3 Overlapping Non-coding RNA (HABON), was not only regulated by hypoxic-induced factor-1α (HIF-1α) but its expression increased significantly under hypoxia in tumour cells. We deciphered the biological characteristics of HABON including its cell localization, genomic location, as well as its full-length sequence, and proved HABON could promote growth, proliferation and clone-formation of hepatocarcinoma cells under hypoxia. Then, we revealed that HABON was transcriptionally activated by HIF-1α in hypoxic cells, furthermore, it could interact with HIF-1α and promote its protein degradation, thus affecting transcription of HIF-1α's target genes to exert its effects on cells. Besides, the elevated expression of HABON under hypoxia could promote the transcriptional activation of BNIP3 through HIF-1α, and increasing the expression level of BNIP3. This research provides a novel clue for the adaptive survival and growth mechanism of tumour under hypoxia, and gives a way to reveal the nature of tumour cells' resistance characteristics to harsh microenvironment.

MicroRNA-630 inhibits breast cancer progression by directly targeting BMI1.

MicroRNAs (miRNAs) play critical roles in breast cancer cell biological processes, including proliferation and apoptosis by inhibiting the expression of their target genes. Herein, we reported that miR-630 overexpression initiates apoptosis, blocks cell cycle progression and suppresses cell proliferation in breast cancer cells. Furthermore, BMI1, a member of polycomb group family, was identified as a direct target of miR-630, and there was a negative correlation between the expression levels of BMI1 and miR-630 in human breast cancer samples. With a series of biology approaches, subsequently, we proved that BMI1 was a functional downstream target of miR-630 and mediated the property of miR-630-dependent inhibition of breast cancer progression. Taken together, these findings provide further evidence on the tumor-suppression function of miR-630 in breast cancer, and clarify BMI1 as a novel functional target gene of miR-630.

YB-1 binds to CAUC motifs and stimulates exon inclusion by enhancing the recruitment of U2AF to weak polypyrimidine tracts.

The human Y box-binding protein-1 (YB-1) is a deoxyribonucleic acid (DNA)/ribonucleic acid (RNA)-binding protein with pleiotropic functions. Besides its roles in the regulation of transcription and translation, several recent studies indicate that YB-1 is a spliceosome-associated protein and is involved in alternative splicing, but the underlying mechanism has remained elusive. Here, we define both CAUC and CACC as high-affinity binding motifs for YB-1 by systematic evolution of ligands by exponential enrichment (SELEX) and demonstrate that these newly defined motifs function as splicing enhancers. Interestingly, on the endogenous CD44 gene, YB-1 appears to mediate a network interaction to activate exon v5 inclusion via multiple CAUC motifs in both the alternative exon and its upstream polypyrimidine tract. We provide evidence that YB-1 activates splicing by facilitating the recruitment of U2AF65 to weak polypyrimidine tracts through direct protein-protein interactions. Together, these findings suggest a vital role of YB-1 in activating a subset of weak 3' splice sites in mammalian cells.

MicroRNA-494 inhibits breast cancer progression by directly targeting PAK1.

MicroRNA (miRNA) is involved in the progression and metastasis of diverse human cancers, including breast cancer, as strong evidence has been found that miRNAs can act as oncogenes or tumor suppressor genes. Here, we show that miR-494 is decreased in human breast cancer specimens and breast cancer cell lines. Ectopic expression of miR-494 in basal-like breast cancer cell lines MDA-MB-231-LUC-D2H3LN and BT-549 inhibits clonogenic ability and metastasis-relevant traits in vitro. Moreover, ectopic expression of miR-494 suppresses neoplasm initiation as well as pulmonary metastasis in vivo. Further studies have identified PAK1, as a direct target gene of miR-494, contributes to the functions of miR-494. Remarkably, the expression of PAK1 is inversely correlated with the level of miR-494 in human breast cancer samples. Furthermore, re-expression of PAK1 partially reverses miR-494-mediated proliferative and clonogenic inhibition as well as migration and invasion suppression in breast cancer cells. Taken together, these findings highlight an important role for miR-494 in the regulation of progression and metastatic potential of breast cancer and suggest a potential application of miR-494 in breast cancer treatment.

MiR-630 suppresses breast cancer progression by targeting metadherin.

MicroRNAs have been integrated into tumorigenic programs as either oncogenes or tumor suppressor genes. The miR-630 was reported to be deregulated and involved in tumor progression of several human malignancies. However, its expression regulation shows diversity in different kinds of cancers and its potential roles remain greatly elusive. Herein, we demonstrate that miR-630 is significantly suppressed in human breast cancer specimens, as well as in various breast cancer cell lines. In aggressive MDA-MB-231-luc and BT549 breast cancer cells, ectopic expression of miR-630 strongly inhibits cell motility and invasive capacity in vitro. Moreover, lentivirus delivered miR-630 bestows MDA-MB-231-luc cells with the ability to suppress cell colony formation in vitro and pulmonary metastasis in vivo. Further studies identify metadherin (MTDH) as a direct target gene of miR-630. Functional studies shows that MTDH contributes to miR-630-endowed effects including cell migration and invasion as well as colony formation in vitro. Taken together, these findings highlight an important role for miR-630 in the regulation of metastatic potential of breast cancer and suggest a potential application of miR-630 in breast cancer treatment.