The ribosome is a structurally and functionally conserved macromolecular machine universally responsible for catalyzing protein synthesis. Within eukaryotic cells, mitochondria contain their own ribosomes (mitoribosomes), which synthesize a handful of proteins, all essential for the biogenesis of the oxidative phosphorylation system. High-resolution cryo-EM structures of the yeast, porcine and human mitoribosomal subunits and of the entire human mitoribosome have uncovered a wealth of new information to illustrate their evolutionary divergence from their bacterial ancestors and their adaptation to synthesis of highly hydrophobic membrane proteins. With such structural data becoming available, one of the most important remaining questions is that of the mitoribosome assembly pathway and factors involved. The regulation of mitoribosome biogenesis is paramount to mitochondrial respiration, and thus to cell viability, growth and differentiation. Moreover, mutations affecting the rRNA and protein components produce severe human mitochondrial disorders. Despite its biological and biomedical significance, knowledge on mitoribosome biogenesis and its deviations from the much-studied bacterial ribosome assembly processes is scarce, especially the order of rRNA processing and assembly events and the regulatory factors required to achieve fully functional particles. This article focuses on summarizing the current available information on mitoribosome assembly pathway, factors that form the mitoribosome assembly machinery, and the effect of defective mitoribosome assembly on human health.

SUMMARY Human mitochondrial ribosomes are specialized in the synthesis of 13 proteins, which are fundamental components of the oxidative phosphorylation system. The pathway of mitoribosome biogenesis, the compartmentalization of the process and factors involved remain largely unknown. Here, we have identified the DEAD box protein DDX28 as an RNA granule component essential for the biogenesis of the mitoribosome large subunit (mt-LSU). DDX28 interacts with the 16S rRNA and the mt-LSU. RNAi-mediated DDX28 silencing in HEK293T cells does not affect mitochondrial mRNA stability, 16S rRNA processing or modification. However, it leads to reduced levels of 16S rRNA and mt-LSU proteins, impaired mt-LSU assembly, deeply attenuated mitochondrial protein synthesis and consequent failure to assemble oxidative phosphorylation complexes. Our findings identify DDX28 as essential during the early stages of mitoribosome mt-LSU biogenesis, a process that mainly takes place near the mitochondrial nucleoids, in the compartment defined by the RNA granules.

MicroRNAs (miRNAs) are short noncoding RNAs derived from the 3′ and 5′ ends of the same precursor. However, the biological function and mechanism of miRNA arm expression preference remain unclear in breast cancer. We found significant decreases in the expression levels of miR-193a-5p but no significant differences in those of miR-193a-3p in breast cancer. MiR-193a-3p suppressed breast cancer cell growth and migration and invasion abilities, whereas miR-193a-5p suppressed cell growth but did not influence cell motility. Furthermore, NLN and CCND1, PLAU, and SEPN1 were directly targeted by miR-193a-5p and miR-193a-3p, respectively, in breast cancer cells. The endogenous levels of miR-193a-5p and miR-193a-3p were significantly increased by transfecting breast cancer cells with the 3′UTR of their direct targets. Comprehensive analysis of The Cancer Genome Atlas database revealed significant differences in the arm expression preferences of several miRNAs between breast cancer and adjacent normal tissues. Our results collectively indicate that the arm expression preference phenomenon may be attributable to the target gene amount during breast cancer progression. The miRNA arm expression preference may be a means of modulating miRNA function, further complicating the mRNA regulatory network. Our findings provide a new insight into miRNA regulation and an application for breast cancer therapy.

Most steps on the biogenesis of the mitochondrial ribosome (mitoribosome) occur near the mitochondrial DNA nucleoid, in RNA granules, which contain dedicated RNA metabolism and mitoribosome assembly factors. Here, analysis of the RNA granule proteome identified the presence of a set of small GTPases that belong to conserved families of ribosome assembly factors. We show that GTPBP10, a member of the conserved Obg family of P-loop small G proteins, is a mitochondrial protein and have used gene-editing technologies to create a HEK293T cell line KO for GTPBP10. The absence of GTPBP10 leads to attenuated mtLSU and mtSSU levels and the virtual absence of the 55S monosome, which entirely prevents mitochondrial protein synthesis. We show that a fraction of GTPBP10 cosediments with the large mitoribosome subunit and the monosome. GTPBP10 physically interacts with the 16S rRNA, but not with the 12S rRNA, and crosslinks with several mtLSU proteins. Additionally, GTPBP10 is indirectly required for efficient processing of the 12S-16S rRNA precursor transcript, which could explain the mtSSU accumulation defect. We propose that GTPBP10 primarily ensures proper mtLSU maturation and ultimately serves to coordinate mtSSU and mtLSU accumulation then providing a quality control check-point function during mtLSU assembly that minimizes premature subunit joining.

Background: Acute kidney injury (AKI) during sepsis is associated with poor outcome. However, diagnosis of AKI with serum creatinine (SCr) level change is neither highly sensitive nor specific. Therefore, identification of novel biomarkers for early diagnosis of AKI is desirable. Aims: To evaluate the capacity of combining urinary netrin-1 and human kidney injury molecule type 1 (KIM-1) in the early diagnosis of septic AKI. Methods: We prospectively recruited 150 septic patients from Jun 2011 to Jun 2013 at Zhejiang Provincial People's Hospital, China. SCr, urinary netrin-1, and KIM-1 levels were recorded at 0, 1, 3, 6, 24, and 48 h of ICU admission and compared between AKI and non-AKI patients. In addition, we investigated the prognostic value of netrin-1 and KIM-1 between non-survivors and survivors in septic AKI patients. Results: SCr levels started to show elevation after 24 h of ICU admission. However, netrin-1 levels increased significantly as early as 1 h, peaked at 3-6 h and remained elevated up to 48 h of ICU admission in septic AKI patients. KIM-1 increased significantly by 6 h, peaked at 24 h and remained significantly elevated until 48 h of ICU admission. Furthermore, we observed significant higher urinary KIM-1 levels at 24 h and 48 h in non-survivors compared to survivors in AKI patients. Conclusions: Our results suggest that both netrin-1 and KIM-1 are clinically useful as early biomarkers in the diagnosis of septic AKI. In addition, persistent elevation of urinary KIM-1 level may be associated with poor prognosis.

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Trichostatin A (TSA) possess histone deacetylase (HDAC) inhibitory potential, can reverse the deactivation of tumor suppressor genes and inhibit tumor cell proliferation. We evaluated the effect of TSA on HDAC expression, tumor cell proliferation, and cancer stem cells (CSCs) activities in pancreatic ductal adenocarnoma (PDAC) cells. The PDAC cell lines MiaPaCa-2 and PANC-1 were distinctly sensitive to TSA, with enhanced apoptosis, compared to SAHA. TSA or SAHA inhibited vimentin, HDACs 1, 7 and 8, upregulated E-cadherin mRNA and protein levels in the PDAC cells, and time-dependently downregulated Oct-4, Sox-2, and Nanog, as well as inhibited PDAC tumorsphere formation. TSA also induces accumulation of acetylated histones, while increasing histone 3 lysine 4 or 9 dimethylation levels in PDAC cells and enhancing the epigenetic activity of SAHA. The anti-CSCs effect of TSA was like that obtained by silencing HDAC-1 or 7 using siRNA, and enhances Gemcitabine activity. Our study highlights the molecular targetability of HDACs 1, 7, and 8, confirm their PDAC-CSCs maintaining role, and demonstrate that compared to SAHA, TSA modulates the epigenetically- mediated oncogenic activity of PDAC-CSCs, and potentiate Gemcitabine therapeutic activity, making a case for further exploration of TSA activity alone or in combination with Gemcitabine in PDAC therapy.