The c-myc proto-oncogene plays a key role in the proliferation, differentiation, apoptosis, and regulation of the cell cycle. Recently, it was demonstrated that the 5 nontranslated region (5 NTR) of human c-myc mRNA contains an internal ribosomal entry site (IRES). In this study, we investigated cellular proteins interacting with the IRES element of c-myc mRNA. Heterogeneous nuclear ribonucleoprotein C (hnRNP C) was identified as a cellular protein that interacts specifically with a heptameric U sequence in the c-myc IRES located between two alternative translation initiation codons CUG and AUG. Moreover, the addition of hnRNP C1 in an in vitro translation system enhanced translation of c-myc mRNA. Interestingly, hnRNP C was partially relocalized from the nucleus, where most of the hnRNP C resides at interphase, to the cytoplasm at the G 2 /M phase of the cell cycle. Coincidently, translation mediated through the c-myc IRES was increased at the G 2 /M phase when cap-dependent translation was partially inhibited. On the other hand, a mutant c-myc mRNA lacking the hnRNP C-binding site, showed a decreased level of translation at the G 2 /M phase compared to that of the wild-type message. Taken together, these findings suggest that hnRNP C, via IRES binding, modulates translation of c-myc mRNA in a cell cycle phase-dependent manner.

Alcoholic liver disease (ALD) refers to the damages to the liver and its functions due to alcohol overconsumption. It consists of fatty liver/steatosis, alcoholic hepatitis, steatohepatitis, chronic hepatitis with liver fibrosis or cirrhosis, and hepatocellular carcinoma. However, the mechanisms behind the pathogenesis of alcoholic liver disease are extremely complicated due to the involvement of immune cells, adipose tissues, and genetic diversity. Clinically, the diagnosis of ALD is not yet well developed. Therefore, the number of patients in advanced stages has increased due to the failure of proper early detection and treatment. At present, abstinence and nutritional therapy remain the conventional therapeutic interventions for ALD. Moreover, the therapies which target the TNF receptor superfamily, hormones, antioxidant signals, and MicroRNAs are used as treatments for ALD. In particular, mesenchymal stem cells (MSCs) are gaining attention as a potential therapeutic target of ALD. Therefore, in this review, we have summarized the current understandings of the pathogenesis and diagnosis of ALD. Moreover, we also discuss the various existing treatment strategies while focusing on promising therapeutic approaches for ALD.

Serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) is the key enzyme in melatonin synthesis regulated by circadian rhythm. To date, our understanding of the oscillatory mechanism of melatonin has been limited to autoregulatory transcriptional and posttranslational regulations of AANAT mRNA. In this study, we identify three proteins from pineal glands that associate with cis-acting elements within species-specific AANAT 3 untranslated regions to mediate mRNA degradation. These proteins include heterogeneous nuclear ribonucleoprotein R (hnRNP R), hnRNP Q, and hnRNP L. Their RNA-destabilizing function was determined by RNA interference and overexpression approaches. Expression patterns of these factors in pineal glands display robust circadian rhythm. The enhanced levels detected after midnight correlate with an abrupt decline in AANAT mRNA level. A mathematical model for the AANAT mRNA profile and its experimental evidence with rat pinealocytes indicates that rhythmic AANAT mRNA degradation mediated by hnRNP R, hnRNP Q, and hnRNP L is a key process in the regulation of its circadian oscillation.Circadian rhythm is a fundamental biological phenomenon in living organisms (10,41,53). To date, efforts to understand the molecular mechanisms of circadian rhythm have focused mainly on transcriptional regulation. A number of studies show that autoregulatory transcriptional-posttranslational feedback loops are crucial for the rhythmic expression of clock-controlled genes (14,30,40,41,46). However, limited data on the posttranscriptional level are available (45). Since mRNA turnover has notable effects on the synthesis of specific proteins and provides the cell with flexibility in achieving rapid changes at the transcript level (9, 35, 50, 52), it is possible that posttranscriptional regulation functions in the rhythmic expression of circadian genes.Recent evidence supports the existence of posttranscriptional mechanisms. In Drosophila, the degradation of Period (per) mRNA modulates its proper circadian fluctuation (49). The accelerated decay of mouse Per1 (mPer1) mRNA in a tau mutant is additionally suggestive of the presence of a posttranscriptional regulatory pathway (32). In transgenic experiments, the differences between the mRNA fluctuations of clock-controlled genes and reporters were tentatively accounted for by variations in their mRNA stability mediated by 3Ј untranslated regions (3ЈUTRs) (22, 51). In computational modeling approaches, mRNA degradation is assumed in the construction of circadian clock models, although its role in rhythm formation is not currently clear (12, 31). Here, we postulate that dynamic mRNA degradation is essential for the formation of circadian rhythms in clock-controlled gene expression, and we support our theory with mathematical modeling and experimental evidence of rat serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) mRNA rhythms.AANAT is a rate-limiting enzyme in the melatonin synthetic pathway that drives the daily rhythm in the leve...

Natural killer (NK) cells play important roles in immune surveillance. However, the tumor microenvironment suppresses NK cell function and allows cancer cells to evade immune detection. In this study, we investigated whether the thyroid cancer cell microenvironment has this effect on NK cells. We found that prostaglandin (PG) E2 produced by thyroid cancer cells suppressed the cytolytic activity of NK cells by inhibiting the expression of the natural cytotoxicity receptors NKp44 and NKp30 and the death receptor tumor necrosis factor-related apoptosis-inducing ligand. PGE2 and cyclooxygenase-2 were highly expressed in thyroid cancer cells; moreover, anaplastic thyroid cancer cells released higher amounts of PGE2 than the papillary subtype, which was associated with suppression of NK cell-inducing nuclear factor-κB and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways via PGE2 receptor (EP) 2 and EP4 expressed on the NK cell surface. In addition, PGE2 inhibited the functional maturation of NK cells and reduced their cytotoxicity against target cells. These results indicate that PGE2 promotes thyroid cancer progression by inhibiting NK cell maturation and cytotoxicity. Thus, therapeutic strategies that target PGE2 in thyroid cancer could potentiate the immune response and improve patient prognosis.

The circadian rhythm of pineal melatonin requires the nocturnal increment of serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) protein. To date, only limited information is available in the critical issue of how AANAT protein expression is up-regulated exclusively at night regardless of its species-specific mRNA profiles. Here we show that the circadian timing of AANAT protein expression is regulated by rhythmic translation of AANAT mRNA. This rhythmic control is mediated by both a highly conserved IRES (internal ribosome entry site) element within the AANAT 5 untranslated region and its partner hnRNP Q (heterogeneous nuclear ribonucleoprotein Q) with a peak in the middle of the night. Consistent with the enhancing role of hnRNP Q in AANAT IRES activities, knockdown of the hnRNP Q level elicited a dramatic decrease of peak amplitude in the AANAT protein profile parallel to reduced melatonin production in pinealocytes. This translational regulation of AANAT mRNA provides a novel aspect for achieving the circadian rhythmicity of vertebrate melatonin.[Keywords: AANAT; translation; IRES; hnRNP Q; melatonin; circadian rhythm] Supplemental Material is available at http://www.genesdev.org.