Severe acute respiratory syndrome coronavirus nonstructural protein 13 (SCV nsP13), a superfamily 1 helicase, plays a central role in viral RNA replication through the unwinding of duplex RNA and DNA with a 5′ single-stranded tail in a 5′ to 3′ direction. Despite its putative role in viral RNA replication, nsP13 readily unwinds duplex DNA by cooperative translocation. Herein, nsP13 exhibited different characteristics in duplex RNA unwinding than that in duplex DNA. nsP13 showed very poor processivity on duplex RNA compared with that on duplex DNA. More importantly, nsP13 inefficiently unwinds duplex RNA by increasing the 5′-ss tail length. As the concentration of nsP13 increased, the amount of unwound duplex DNA increased and that of unwound duplex RNA decreased. The accumulation of duplex RNA/nsP13 complexes increased as the concentration of nsP13 increased. An increased ATP concentration in the unwinding of duplex RNA relieved the decrease in duplex RNA unwinding. Thus, nsP13 has a strong affinity for duplex RNA as a substrate for the unwinding reaction, which requires increased Atps to processively unwind duplex RnA. our results suggest that duplex RnA is a preferred substrate for the helicase activity of nsP13 than duplex DNA at high ATP concentrations.Severe acute respiratory syndrome (SARS) is an acute respiratory infectious disease caused by a novel coronavirus (SARS-CoV or SCV) that has claimed almost 800 deaths in early 2003 1 . SCV is an enveloped, positive single-stranded RNA virus (or (+) ssRNA virus) with a genome of ~30 kb in length 2,3 . Two-thirds of the SCV genome at the 5′-end comprise replicase genes (orf1ab) encoding 16 nonstructural proteins (nsPs). The replicase genes comprising open reading frames (OFR1a and 1b) are translated into two large replicative polyproteins, pp1ab (~790 kDa) and pp1a (~490 kDa), which are involved with and without ribosomal frameshifting into the −1 frame 4,5 . These two translational polyproteins are processed autoproteolytically by the major viral cysteine proteases M PRO or 3CL PRO to produce 16 non-structural proteins (nsPs), including RNA-dependent RNA polymerases (RdRp, nsP12) and NTPase/helicase (nsP13) 6-8 . These viral replicases are the core of membrane-bound replication-transcription complexes that synthesize the entire viral genome and eight subgenomic mRNAs 9,10 .Because viral helicase is considered to be essential for subsequent viral replication and proliferation, it is an important potential target for antiviral therapy [11][12][13] . In addition, the inhibition of these targets may interfere with the metabolism of the infecting virus without strong side effects in patients. Several viral helicases have been used as proven drug targets due to the inhibition of helicase activity in animal models of herpes simplex virus (HSV) and in the treatment of hepatitis C 14,15 . Therefore, much effort has been spent on the development of small-molecule inhibitors and chemicals as drug candidates to inhibit the function of SARS coronavirus helicase nsP13 (SCV ns...

Tumor angiogenesis is one of the major hallmarks of tumor progression. Nobiletin is a natural flavonoid isolated from citrus peel that has anti-angiogenic activity. Steroid receptor coactivator (Src) is an intracellular tyrosine kinase so that focal adhesion kinase (FAK) binds to Src to play a role in tumor angiogenesis. Signal transducer and activator of transcription 3 (STAT3) is a marker for tumor angiogenesis which interacts with Src. Paxillin (PXN) acts as a downstream target for both FAK and STAT3. The main goal of this study was to assess inhibition of tumor angiogenesis by nobiletin in estrogen receptor positive (ER+) breast cancer cells via Src, FAK, and STAT3-mediated signaling through PXN. Treatment with nobiletin in MCF-7 and T47D breast cancer cells inhibited angiogenesis markers, based on western blotting and RT-PCR. Validation of in vitro angiogenesis in the human umbilical vein endothelial cells (HUVEC) endothelial cell line proved the anti-angiogenic activity of nobiletin. Electrophoretic mobility shift assay and the ChIP assay showed that nobiletin inhibits STAT3/DNA binding activity and STAT3 binding to a novel binding site of the PXN gene promoter. We also investigated the migration and invasive ability of nobiletin in ER+ cells. Nobiletin inhibited tumor angiogenesis by regulating Src, FAK, and STAT3 signaling through PXN in ER+ breast cancer cells.

Targeted cancer therapy with natural compounds is more effective than nontargeted therapy. Nobiletin is a flavonoid derived from citrus peel that has anticancer activity. Cluster of differentiation 36 (CD36) is a member of the class B scavenger receptor family that is involved in importing fatty acids into cells. CD36 plays a role in tumor angiogenesis by binding to its ligand, thrombospondin-1 (TSP-1), and then interacting with transforming growth factor beta 1 (TGFβ1). CD36 is implicated in tumor metastasis through its roles in fatty acid metabolism. This study investigated the molecular mechanisms underlying nobiletin’s anticancer activity by characterizing its interactions with CD36 as the target molecule. We hypothesize that the anti-angiogenic activity of nobiletin involving its regulation of CD36 via signal transducer and activator of transcription 3 (STAT3) rather than through TSP-1. Gene analysis identified a Gamma interferon activation site (GAS) element in the CD36 gene promoter that acts as a STAT3 binding site, an interaction that was confirmed by ChIP assay. STAT3 interacts with nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), suggesting that nobiletin also acts through the CD36/ (STAT3)/NF-κB signaling axis. Nobiletin inhibited CD36-dependent breast cancer cell migration and invasion as well as CD36-mediated tumor sphere formation. Taken together, these results suggest that nobiletin inhibits cancer stem cells in multiple ways.

The major hallmarks of tumor progression are angiogenesis, migration and metastasis. Among the components of Rhodiola rosea, salidroside (p‑hydroxyphenethyl-β‑d-glucoside) is one of the most potent, and is present in all Rhodiola species. Recent data have revealed the anticancer effects of salidroside; however, the mechanism underlying its ability to inhibit tumor angiogenesis remains unknown. The present study aimed to analyze how salidroside affects major factors involved in breast cancer, and to elucidate its ability to inhibit angiogenesis and invasion. Signal transducer and activator of transcription 3 (STAT3) is a marker for tumor angiogenesis and migration, which interacts with matrix metalloproteinases (MMPs). Specifically, MMPs act as a downstream target for STAT3. Using western blotting and reverse transcription-quantitative polymerase chain reaction analysis, the present study demonstrated that treatment of MDA‑MB 231 triple-negative breast cancer (TNBC) cells with salidroside led to inhibition of invasion and migration markers, and of STAT3 signaling. Furthermore, in vitro angiogenesis analyses in human umbilical vein endothelial cells confirmed the anti-angiogenic activity of salidroside. An electrophoretic mobility shift assay also demonstrated that salidroside may inhibit the DNA-binding activity of STAT3, preventing STAT3 from binding to a novel binding site of the MMP2 gene promoter. In conclusion, the present results demonstrated that salidroside may downregulate the STAT3 signaling pathway, and inhibit cell viability, migration and invasion through MMPs in breast cancer cells.

Tannic acid (TA), a naturally occurring polyphenol, is a potent anti‐oxidant with anti‐proliferative effects on multiple cancers. However, its ability to modulate gene‐specific expression of tumour suppressor genes and oncogenes has not been assessed. This work investigates the mechanism of TA to regulate canonical and non‐canonical STAT pathways to impose the gene‐specific induction of G1‐arrest and apoptosis. Regardless of the p53 status and membrane receptors, TA induced G1‐arrest and apoptosis in breast cancer cells. Tannic acid distinctly modulated both canonical and non‐canonical STAT pathways, each with a specific role in TA‐induced anti‐cancer effects. Tannic acid enhanced STAT1 ser727 phosphorylation via upstream serine kinase p38. This STAT1 ser727 phosphorylation enhanced the DNA‐binding activity of STAT1 and in turn enhanced expression of p21Waf1/Cip1. However, TA binds to EGF‐R and inhibits the tyrosine phosphorylation of both STAT1 and STAT3. This inhibition leads to the inhibition of STAT3/BCL‐2 DNA‐binding activity. As a result, the expression and mitochondrial localization of BCl‐2 are declined. This altered expression and localization of mitochondrial anti‐pore factors resulted in the release of cytochrome c and the activation of intrinsic apoptosis cascade involving caspases. Taken together, our results suggest that TA modulates EGF‐R/Jak2/STAT1/3 and P38/STAT1/p21Waf1/Cip1 pathways and induce G1‐arrest and intrinsic apoptosis in breast carcinomas.