Yoshiyuki Takei Jak inhibitor induces S phase cell-cycle arrest and augments TRAIL-induced apoptosis in human hepatocellular carcinoma cells
Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in various cancers and plays a crucial role in oncogensis, including the activation of genes encoding apoptosis inhibitors and cell-cycle regulators. We investigated the biological significance of the Janus kinase (Jak)-STAT pathway in human hepatocellular carcinoma (HCC). Constitutive activation of STAT3 was seen in 49.4% of human HCC specimens and in HCC cell lines. Jak inhibitor AG490 inhibited activation of STAT3 and markedly reduced cell viability without significant apoptosis. AG490 also induced S phase cell-cycle arrest with down-regulation of cyclin D1, A, E and up-regulation of p21, p27, phospho-Chk2. AG490 also inhibited caspase inhibitory proteins, such as XIAP and survivin, and augmented TRAIL-induced apoptosis. Our study suggests that the Jak-STAT pathway plays an important role in cell-cycle progression and resistance to apoptosis. Inhibition of the Jak-STAT pathway may thus be a therapeutic target for HCC.
Available from: Farrukh Aqil
- "We observed a dramatic decrease in the expression of Cdc25A and Cdk2 proteins in Tan IIA treated cells, leading to reduction of Cdc25A phosphatase activity, which was also evidenced by the increase of inhibitory phosphorylated p-Cdk2 (Tyr15). Rb protein being direct substrate of Cdk2 kinase, a decrease in Rb phosphorylation was observed in Tan IIA treated cells and seemed to be consistent with the Cdk2 inhibition  . "
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ABSTRACT: Human papilloma virus (HPV) is the well-established etiological factor of cervical cancer. E6 and E7 oncoproteins expressed by HPV are known to inactivate tumor suppressor proteins p53 and pRb, respectively. Tanshinone IIA (Tan IIA) is a diterpenoid naphthoquinone found in the traditional Chinese medicine Danshen (Salvia sp). Tan IIA has been shown to possess anti-tumor activity against several cancer types. In this study we show that Tan IIA potently inhibited proliferation of the human cervical cancer cells CaSki, SiHa, HeLa and C33a. Mechanistically in HPV positive CaSki cells, Tan IIA was found to i) downregulate expression of HPV E6 and E7 genes and modulate associated proteins E6AP and E2F1, ii) cause S phase cell cycle arrest, iii) induce accumulation of p53 and alter expression of p53-dependent targets, iv) modulate pRb and related proteins, and v) cause p53-mediated apoptosis by moderating Bcl2, Bax, caspase-3, and PARP cleavage expressions. In vivo, Tan IIA resulted in over 66% reduction in tumor volume of cervical cancer xenograft in athymic nude mice. Tan IIA treated tumor tissues had lower expression of proliferation marker PCNA and changes in apoptosis targets were in agreement with in vitro studies, further confirming reduced proliferation and involvement of multiple targets behind anti-cancer effects. This is the first demonstration of Tan IIA to possess significant anti-viral activity by repressing of HPV oncogenes leading to inhibition of cervical cancer. Together, our data suggest that Tan IIA can be exploited as a potent therapeutic agent for the prevention and treatment of cervical and other HPV-related cancers.
Available from: Alan Prem Kumar
- "We found that lupeol also suppressed STAT3 activation induced by IL - 6 , one of the many tumour cell growth factors that activate STAT3 ( Bromberg and Wang , 2009 ) . The doses required to inhibit STAT3 activation were more or less comparable to rationally designed pharmaco - logical blockers that inhibit STAT3 dimerisation ( Fuke et al , 2007 ) . The inhibitory effects of lupeol on STAT3 phosphorylation correlated with the suppression of activation of upstream protein tyrosine kinases ( c - Src , JAK1 and JAK2 ) in a time - dependent manner in HCC cells . "
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ABSTRACT: Background: Constitutive activation of signal transducer and activator of transcription signalling 3 (STAT3) has been linked with survival, proliferation and angiogenesis in a wide variety of malignancies including hepatocellular carcinoma (HCC).
Methods: We evaluated the effect of lupeol on STAT3 signalling cascade and its regulated functional responses in HCC cells.
Results: Lupeol suppressed constitutive activation of STAT3 phosphorylation at tyrosine 705 residue effectively in a dose- and time-dependent manner. The phosphorylation of Janus-activated kinases (JAKs) 1 and 2 and Src was also suppressed by lupeol. Pervanadate treatment reversed the downregulation of phospho-STAT3 induced by lupeol, thereby indicating the involvement of a phosphatase. Indeed, we observed that treatment with lupeol increased the protein and mRNA levels of SHP-2, and silencing of SHP-2 abolished the inhibitory effects of lupeol on STAT3 activation. Treatment with lupeol also downregulated the expression of diverse STAT3-regulated genes and decreased the binding of STAT3 to VEGF promoter. Moreover, the proliferation of various HCC cells was significantly suppressed by lupeol, being associated with substantial induction of apoptosis. Depletion of SHP-2 reversed the observed antiproliferative and pro-apoptotic effects of lupeol.
Conclusions: Lupeol exhibited its potential anticancer effects in HCC through the downregulation of STAT3-induced pro-survival signalling cascade.
Available from: Linhong Deng
- "The different levels of SOCS-1 as shown in Table 1, and perhaps other components in the pathway may determine the different chemoresistance of HepG2 and Hep3B to drug treatments. AG490 is a JAK2 specific inhibitor that inhibits the phosphorylation of STAT3 (Fuke et al. 2007; Kusaba et al. 2007). Treatment with AG490 induces cell cycle arrest in HepG2 cells but obvious apoptosis in Hep3B cells (Kusaba et al. 2007). "
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ABSTRACT: As cellular models for in vitro liver cancer and toxicity studies, HepG2 and Hep3B are the two most frequently used liver cancer cell lines. Because of their similarities they are often treated as the same in experimental studies. However, there are many differences that have been largely over-sighted or ignored between them. In this review, we summarize the differences between HepG2 and Hep3B cell lines that can be found in the literature based on PubMed search. We particularly focus on the differential gene expression, differential drug responses (chemosensitivity, cell cycle and growth inhibition, and gene induction), signaling pathways associated with these differences, as well as the factors in governing these differences between HepG2 and Hep3B cell lines. Based on our analyses of the available data, we suggest that neither HBx nor p53 may be the crucial factor to determine the differences between HepG2 and Hep3B cell lines although HBx regulates the expression of the majority of genes that are differentially expressed between HepG2 and Hep3B. Instead, the different maturation stages in cancer development of the original specimen between HepG2 and Hep3B may be responsible for the differences between them. This review provides insight into the molecular mechanisms underlying the differences between HepG2 and Hep3B and help investigators especially the beginners in the areas of liver cancer research and drug metabolism to fully understand, and thus better use and interpret the data from these two cell lines in their studies.
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