[Show abstract][Hide abstract] ABSTRACT: Accumulating evidence has implicated the deregluation of miRNAs in tumorigenesis. Previous studies have reported that microRNA-195 (miR-195) is markedly down-regulated in human glioblastoma cells, compared with normal brain tissue, but the biological role of miR-195 in glioblastoma development is currently unknown. In this study, we define a tumor-suppressor role for miR-195 in human glioblastoma cells. Over-expression of miR-195 in glioblastoma cell lines robustly arrested cell cycle progression and significantly repressed cellular invasion. We identified E2F3 and CCND3 as functional downstream targets of miR-195 in glioblastoma cells. Through knockdown studies, we demonstrated that E2F3 was the dominant effector of miR-195-mediated cell cycle arrest and that CCND3 was a key mediator of miR-195-induced inhibition of glioblastoma cell invasion. Furthermore, we showed that p27(Kip1) was an important regulator downstream of CCND3 and that the accumulation of p27(Kip1) in the cytoplasm might be responsible for the miR-195-mediated cell invasion inhibition in glioblastoma cells. This work provides evidence for the initial mechanism by which miR-195 negatively regulates both the proliferation and invasion of glioblastoma cells, suggesting that the down-regulation of miR-195 might contribute to the malignant transformation of glioblastoma cells and could be a molecular signature associated with glioblastoma progression.
[Show abstract][Hide abstract] ABSTRACT: MicroRNAs (miRNAs) are approximately 22-nt small non-coding regulatory RNAs that have generally been considered to regulate gene expression at the post-transcriptional level in the cytoplasm. However, recent studies have reported that some miRNAs localize to and function in the nucleus.
To determine the number of miRNAs localized to the nucleus, we systematically investigated the subcellular distribution of small RNAs (sRNAs) by independent deep sequencing sequenced of the nuclear and cytoplasmic pools of 18- to 30-nucleotide sRNAs from human cells. We identified 339 nuclear and 324 cytoplasmic known miRNAs, 300 of which overlap, suggesting that the majority of miRNAs are imported into the nucleus. With the exception of a few miRNAs evidently enriched in the nuclear pool, such as the mir-29b, the ratio of miRNA abundances in the nuclear fraction versus in the cytoplasmic fraction vary to some extent. Moreover, our results revealed that a large number of tRNA 3' trailers are exported from the nucleus and accumulate in the cytoplasm. These tRNA 3' trailers accumulate in a variety of cell types, implying that the biogenesis of tRNA 3' trailers is conserved and that they have a potential functional role in vertebrate cells.
Our results provide the first comprehensive view of the subcellular distribution of diverse sRNAs and new insights into the roles of miRNAs and tRNA 3' trailers in the cell.
PLoS ONE 05/2010; 5(5):e10563. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Deposition of collagen IV in proximal tubule cells (PTCs) plays an important role during diabetic nephropathy, but the mechanism underlying excessive production of collagen IV remains poorly understood. In this study, we examined the miRNA profile of HK-2 cells and found that high glucose/TGF-beta1 induced significant down-regulation of miR-29a. We then showed that miR-29a negatively regulated collagen IV by directly targeting the 3'UTRs of col4a1 and col4a2. These results suggest that miR-29a acts as a repressor to fine-tune collagen expression and that the reduction of miR-29a caused by high glucose may increase the risk of excess collagen deposition in PTCs.
[Show abstract][Hide abstract] ABSTRACT: Giardia lamblia is an early diverging and evolutionarily successful protozoan as it can enter into a dormant cyst stage from a vegetative trophozoite. During dormant stage, its metabolic rate decreases dramatically. However, to date, the regulatory molecules participating in the initiation and maintenance of this process have not been fully investigated. In this study, we have identified a class of abundant small RNAs named sitRNAs, which are approximately 46 nucleotides in length and accumulate in G. lamblia encysting cultures. Remarkably, they are derived from the 3' portion of fully matured tRNAs by cleavage of the anticodon left arm, with the 3' terminal CCA triplex still connected. During differentiation, only a limited portion of mature tRNAs is cleaved, but this cleavage occurs almost in the entire tRNA family. sitRNAs begin to accumulate as early as 3 h after initiation of encystation and are maintained at a relatively stable level during the whole process, exhibiting an expression peak at around 24 hr. Our studies further show that sitRNAs can be induced by several other stress factors, and in the case of serum deprivation, both tRNAs and sitRNAs degrade rapidly, with the accumulation of tRNA being halved. Our results may provide new insight into a novel mechanism for stressed G. lamblia to regulate gene expression globally.
Nucleic Acids Research 10/2008; 36(19):6048-55. · 8.81 Impact Factor