No abstract

In this report, we investigated the pathophysiology of a novel hypertension-associated mitochondrial tRNAAla 5655A → G (m.5655A → G) mutation. The destabilization of a highly conserved base pairing (A1-U72) at the aminoacyl acceptor stem by an m.5655A → G mutation altered the tRNAAla function. An in vitro processing analysis showed that the m.5655A → G mutation reduced the efficiency of tRNAAla precursor 5′ end cleavage catalyzed by RNase P. By using cybrids constructed by transferring mitochondria from lymphoblastoid cell lines derived from a Chinese family into mitochondrial DNA (mtDNA)-less (ρo) cells, we showed a 41% reduction in the steady-state level of tRNAAla in mutant cybrids. The mutation caused an improperly aminoacylated tRNAAla, as suggested by aberrantly aminoacylated tRNAAla and slower electrophoretic mobility of mutated tRNA. A failure in tRNAAla metabolism contributed to variable reductions in six mtDNA-encoded polypeptides in mutant cells, ranging from 21% to 37.5%, with an average of a 29.1% reduction, compared to levels of the controls. The impaired translation caused reduced activities of mitochondrial respiration chains. Furthermore, marked decreases in the levels of mitochondrial ATP and membrane potential were observed in mutant cells. These caused increases in the production of reactive oxygen species in the mutant cybrids. The data provide evidence for the association of the tRNAAla 5655A → G mutation with hypertension.

No abstract

Organic anion transporting polypeptides (OATPs) have been extensively recognized as key determinants of absorption, distribution, metabolism and excretion (ADME) of various drugs, xenobiotics and toxins. Putative N-glycosylation sites located in the extracellular loops 2 and 5 is considered a common feature of all OATPs and some members have been demonstrated to be glycosylated proteins. However, experimental evidence is still lacking on how such a post-translational modification affect the transport activity of OATPs and which of the putative glycosylation sites are utilized in these transporter proteins. In the present study, we substituted asparagine residues that are possibly involved in N-glycosylation with glutamine residues and identified three glycosylation sites (Asn134, Asn503 and Asn516) within the structure of OATP1B1, an OATP member that is mainly expressed in the human liver. Our results showed that Asn134 and Asn516 are used for glycosylation under normal conditions; however, when Asn134 was mutagenized, an additional asparagine at position 503 is involved in the glycosylation process. Simultaneously replacement of all three asparagines with glutamines led to significantly reduced protein level as well as loss of transport activity. Further studies revealed that glycosylation affected stability of the transporter protein and the unglycosylated mutant was retained within endoplasmic reticulum.

Increasing evidence indicates that long non-coding RNA (lncRNA) plays an important role in tumorigenesis. However, the function and regulatory mechanism of lncRNAs are still unclear in esophageal squamous cell carcinoma (ESCC). To address this challenge, we screened lncRNAs expression profiles in 3 pairs of ESCC and matched non-cancerous tissues by microarray assay and identified the relationship between lncRNAs expression in ESCC tissue and clinicopathological characteristics and prognosis of patients with ESCC. We found 182 lncRNAs that were significantly differently expressed in ESCC tissues versus the matched non-cancerous tissues. Gene ontology and pathway analysis results suggested that the primary biological processes of these genes were involved in extracellular matrix, immune responses, cell differentiation and cell proliferation. Through cis and trans analyzing, we found 4 lncRNAs (ENST00000480669, NONHSAT104436, NONHSAT126998 and NONHSAT112918) may play important roles in tumorigenesis of ESCC. The four lncRNAs were checked in 73 patients with ESCC. The results showed that they mainly related to tumor metastasis. Kaplan-Meier survival analysis showed that high expression of NONHSAT104436, NONHSAT126998 and low expression of ENST00000480669 were related to poor 3-year overall survival (P=0.003, 0.032 and 0.040, respectively). Multivariate analysis showed that NONHSAT104436 was an independent prognostic factor (P=0.017). Thus we concluded that, lncRNAs showed differently expression patterns in ESCC versus matched non-cancerous tissues, and aberrantly expressed lncRNA may play important roles in ESCC development and progression. Interestingly, the overexpression of NONHSAT104436 was tightly correlated with distant metastasis and, poor survival rate, which might indicate that NONHSAT104436 might play a very important part in ESCC tumor progression.