Antiproliferative effect of urolithin A, the ellagic acid-derived colonic metabolite, on hepatocellular carcinoma HepG2. 2. 15 cells by targeting Lin28a/let-7a axis

An abnormality in the Lin28/let-7a axis is relevant to the progression of hepatitis B virus (HBV)-positive hepatocellular carcinoma (HCC), which could be a novel therapeutic target for this malignant tumor. The present study aimed to investigate the antiproliferative and anti-invasive effects of urolithin A in a stable full-length HBV gene integrated cell line HepG2.2.15 using CCK-8 and transwell assays. The RNA and protein expressions of targets were assessed by quantitative PCR and western blot, respectively. Results revealed that urolithin A induced cytotoxicity in HepG2.2.15 cells, which was accompanied by the cleavage of caspase-3 protein and down-regulation of Bcl-2/Bax ratio. Moreover, urolithin A suppressed the protein expressions of Sp-1, Lin28a, and Zcchc11, and elevated the expression of microRNA let-7a. Importantly, urolithin A also regulated the Lin28a/let-7a axis in transient HBx-transfected HCC HepG2 cells. Furthermore, urolithin A decelerated the HepG2.2.15 cell invasion, which was involved in suppressing the let-7a downstream factors HMGA2 and K-ras. These findings indicated that urolithin A exerted the antiproliferative effect by regulating the Lin28a/let-7a axis and may be a potential supplement for HBV-infected HCC therapy.

Clinicopathological Characteristics of Patients with Gastric Cancer according to the Expression of LIN28A

BACKGROUND/AIMS: Although LIN28A is known to potentially play a role in the oncogenesis of various cancers, whether LIN28A expression is a predictor of poor prognosis in patients with gastric cancer has not been fully explored. We sought to evaluate clinicopathological characteristics according to the expression of LIN28A in numerous gastric cancer tissue samples. METHODS: LIN28A expression was evaluated by immunohistochemical (IHC) analysis of a tissue microarray comprising 288 gastric cancer tissues and 288 adjacent normal tissues. Clinicopathological characteristics, including overall survival, were compared according to LIN28A expression. RESULTS: The IHC staining score was lower for the cancer tissues than the normal tissues (p<0.001). However, no significant differences were observed in the clinicopathological characteristics between the low and high LIN28A expression groups. In addition, the 5-year overall survival rate did not differ between the two groups: 75.3% (95% confidence interval [CI], 69.3% to 81.7%) versus 71.6% (95% CI, 63.3% to 80.9%) for low versus high expression, respectively. CONCLUSIONS: The expression of LIN28A did not appear to play a distinct role in predicting the clinicopathological characteristics of patients with gastric cancer. In addition, LIN28A expression was not an independently associated factor for overall survival in patients with gastric cancer.

Biogenesis and regulation of the let-7 miRNAs and their functional implications

The let-7 miRNA was one of the first miRNAs discovered in the nematode, Caenorhabditis elegans, and its biological functions show a high level of evolutionary conservation from the nematode to the human. Unlike in C. elegans, higher animals have multiple isoforms of let-7 miRNAs; these isoforms share a consensus sequence called the 'seed sequence' and these isoforms are categorized into let-7 miRNA family. The expression of let-7 family is required for developmental timing and tumor suppressor function, but must be suppressed for the self-renewal of stem cells. Therefore, let-7 miRNA biogenesis must be carefully controlled. To generate a let-7 miRNA, a primary transcript is produced by RNA polymerase II and then subsequently processed by Drosha/DGCR8, TUTase, and Dicer. Because dysregulation of let-7 processing is deleterious, biogenesis of let-7 is tightly regulated by cellular factors, such as the RNA binding proteins, LIN28A/B and DIS3L2. In this review, we discuss the biological functions and biogenesis of let-7 miRNAs, focusing on the molecular mechanisms of regulation of let-7 biogenesis in vertebrates, such as the mouse and the human.