Superinduction of P-glycoprotein messenger RNA in vivo in the presence of transcriptional inhibitors

Mechanism and treatment of α-amanitin poisoning

Amanita poisoning has a high mortality rate. The α-amanitin toxin in Amanita is the main lethal toxin. There is no specific detoxification drug for α-amanitin, and the clinical treatment mainly focuses on symptomatic and supportive therapy. The pathogenesis of α-amanitin mainly includes: α-amanitin can inhibit the activity of RNA polymeraseII in the nucleus, including the inhibition of the largest subunit of RNA polymeraseII, RNApb1, bridge helix, and trigger loop. In addition, α-amanitin acts in vivo through the enterohepatic circulation and transport system. α-Amanitin can cause the cell death. The existing mechanisms of cell damage mainly focus on apoptosis, oxidative stress, and autophagy. In addition to the pathogenic mechanism, α-amanitin also has a role in cancer treatment, which is the focus of current research. The mechanism of action of α-amanitin on the body is still being explored.

BAG3 Suppresses Loading of Ago2 to IL6 mRNA in Pancreatic Ductal Adenocarcinoma

Pancreatic stellate cells (PSCs) are a subset of pancreatic cancer-associated fibroblasts, which play a critical role in pancreatic fibrosis, a characteristic feature of pancreatic cancer. The interplay between PSCs and pancreatic cancer cells is vital for promotion of tumor progression and metastasis. BAG3 is correlated with poor prognostics in patients with pancreatic ductal adenocarcinoma (PDAC), however, the exact mechanisms remain largely unknown. In this study, we demonstrated that BAG3 downregulation decreased IL6 release by PDACs, and IL6 reduction was, at least partially, responsible for suppression of PSCs activation by PDACs with BAG3 downmodulation. Importantly, BAG3 expression positively correlated with fibrosis in pancreatic cancer tissue. With regard to the underlying mechanism, we demonstrated that BAG3 knockdown facilitated recruitment of Agonaute 2 (Ago2) to IL6 mRNA, resulting in destabilization of IL6 mRNA. In addition, the current study demonstrated that phosphorylation at Serine (Ser) 387 site was required for recruitment of Ago2-containing miRISC to IL6 mRNA and BAG3 knockdown facilitated Ago2 loading to IL6 mRNA via increasing its phosphorylation at Ser 387. This study shed new light on the tumor-promoting role of BAG3 in PDAC tumors, suggesting BAG3 might represent an interesting therapeutic opportunity to PDAC patients.

Estradiol induces transcriptional and posttranscriptional modifications in versican expression in the mouse uterus

We have previously shown the differential expression of versican in the mouse uterus under ovarian hormone influence. We also demonstrated there is not a direct correlation between mRNA levels and protein expression, suggesting posttranscriptional events, such as alteration in mRNA stability. This posttranscriptional effect may result in the elongation and stabilization of transcripts poly(A) tail. Thus, the aim of this study was to analyze whether estradiol (E2) regulates versican mRNA stability and expression in a dose-related and time-dependent manner. For this purpose female mice were ovariectomized and treated with a single injection of 0.1 or 10 μg E2. To block transcription a group of females received a single injection of alpha-amanitin before hormone administration. Uterine tissues were collected 30 min, 1, 3, 6, 12 and 24 h after treatments and processed for quantitative real time PCR (qPCR), RACE-PAT Assay and immunohistochemistry. qPCR showed that versican mRNA levels are higher than control from 3 to 24 h after E2 administration, whereas after transcription inhibition versican mRNA unexpectedly increases within 3 h, which can be explained when transcriptional blockers alter the degradation rate of the transcript, resulting in the superinduction of this mRNA. Accordingly, analysis of versican transcript poly(A) tail evidenced a longer product 3 h after treatment, but not after 12 h. Versican immunoreaction becomes conspicuous in the superficial stroma only 3 h after E2 injection, whereas the whole stroma is immunoreactive from 6 h onward. These results demonstrate that E2 modulates versican at the transcriptional and posttranscriptional levels in a time-dependent manner.

The effects of ABCB1 3'-untranslated region variants on mRNA stability

Genetic variation in ABCB1, encoding P-glycoprotein (P-gp), is a potential cause of interindividual variation in drug response. Numerous studies have focused on the effects of coding region variants on P-gp expression and function, whereas few noncoding region variants have been investigated. The 3'-untranslated region (UTR) regulates mRNA levels or stability via RNA-protein interactions with mRNA degradation machinery. mRNA stability is a key regulatory step controlling ABCB1 mRNA expression that ultimately affects P-gp levels and function. We hypothesized that ABCB1 3'-UTR polymorphisms alter mRNA stability by disrupting RNA-protein interactions. An ethnically diverse panel of DNA samples was sequenced to identify 3'-UTR polymorphisms and determine allele frequencies. The three most common variants, along with reference ABCB1, were stably expressed in cells in order to measure mRNA half-life. The calculated half-life for ABCB1 reference in HEK293 cells was 9.4 +/- 1.3 h and was similar to that estimated for the 3'-UTR variants. Endogenous ABCB1 mRNA decay was similar in lymphoblastoid cell lines carrying 3'-UTR variant and reference alleles. Although the examined ABCB1 3'-UTR variants have no effect on ABCB1 mRNA stability, these data represent one of the first attempts to determine the influence of genetic variation in UTRs on ABCB1 mRNA levels.

Human intestinal P-glycoprotein activity estimated by the model substrate digoxin

OBJECTIVE

P-glycoprotein (Pgp) plays a part in the intestinal uptake of xenobiotics and has been associated with susceptibility to ulcerative colitis. The aim of this study was to examine Pgp activity in relation to age, gender, medical treatment (rifampicin or ketoconazole) and the multidrug resistance (MDR1) gene single nucleotide polymorphisms (SNPs) G2677T and C3435T using the model drug digoxin.

MATERIAL AND METHODS

Pgp activity was estimated from the pharmacokinetics of orally administered digoxin in blood samples from 32 healthy subjects. MDR1 gene expression in duodenal biopsies was monitored by real-time quantitative RT-PCR (RQ-PCR) and Western blot analyses. MDR1 SNPs were determined by PCR-restriction fragment length polymorphism (PCR-RFLP). The effect of medical treatment was tested by open, randomized, cross-over treatment with rifampicin and ketoconazole.

RESULTS

Rifampicin treatment resulted in increased Pgp activity, duodenal MDR1 mRNA expression and Pgp detection compared with that in the control group (p<0.05 for all), Pgp activity being associated with duodenal MDR1 mRNA level (p<0.05). Individuals homozygous for the 3435 wild-type allele (CC) showed higher Pgp activity (p<0.05), whereas SNP 2677 apparently did not affect Pgp activity. No variation in Pgp in relation to age or gender was found.

CONCLUSIONS

Our data confirm that rifampicin increases Pgp activity, by increasing MDR1 mRNA and Pgp levels. Moreover, we found that the wild-type allele of the synonymous polymorphism of MDR1 position 3435 confers a higher Pgp activity. These data support other findings suggesting an effect of Pgp on treatment response and disease susceptibility.

Identification of in vivo P-glycoprotein mRNA decay intermediates in normal liver but not in liver tumors

Post-transcriptional regulation at the level of mRNA stability is one important mechanism for over-expression of P-glycoprotein (Pgp) genes observed in cultured cells and in animals. A previous study has shown that mRNA half-lives for Pgp genes in normal liver were less than 2 h, in contrast to greater than 12 h measured in a transplantable liver tumor line. This lower turnover rate of Pgp mRNA may, in large part, contribute to the abundance of Pgp mRNA in liver tumors. The current study sought to investigate the underlying mechanism for the lower turnover rate of Pgp2 mRNA previously determined in liver tumors. As a first approach, we set out to understand the Pgp2 mRNA decay in both normal liver and liver tumors by first identifying and characterizing Pgp2 mRNA degradation intermediates. In this study, we showed that the sensitive ligation-mediated polymerase chain reaction (LM-PCR) method can be used to detect a homogenous pool of in vitro transcribed RNA down to 0.4 ng. By employing gene-specific primers in the LM-PCR method, we successfully identified four Pgp2 mRNA decay intermediates in normal liver. All four decay intermediates detected correspond to the 5' coding region of Pgp2 mRNA, and surprisingly no decay intermediates which correspond to 3' untranslated region, 3' coding region or middle coding region were found using LM-PCR. The identified decay intermediates are unique to the normal liver as they were absent or present at very low level in all three liver tumor samples analyzed. This observation supports our previous findings that the Pgp mRNA turnover rate is lower in liver tumors than in normal liver. These findings have implications for our understanding of the regulation of Pgp mRNA turnover in normal and malignant tissues.