Manumycin A induces apoptosis in malignant pleural mesothelioma through regulation of Sp1 and activation of the mitochondria-related apoptotic pathway.

Manumycin A (Manu A) is a natural product isolated from Streptomyces parvulus and has been reported to have anti-carcinogenic and anti-biotic properties. However, neither its molecular mechanism nor its molecular targets are well understood. Thus, the aim of the present study was to explore the possibility that Manu A has cancer preventive and chemotherapeutic effects on malignant pleural mesothelioma (MPM) through regulation of Sp1 and induction of mitochondrial cell death pathway. Manu A inhibited the cell viability of MSTO-211H and H28 cells in a concentration­dependent manner as determined by MTS assay. IC50 values were calculated as 8.3 and 4.3 µM in the MSTO-311H and H28 cells following 48 h incubation, respectively. Manu A induced a significant increase in apoptotic indices as shown by DAPI staining, Annexin V assay, multi-caspase activity and mitochondrial membrane potential assay. The downregulation of Sp1 mRNA and protein expression by Manu A led to apoptosis by suppressing Sp1-regulated proteins (cyclin D1, Mcl-1 and survivin). Manu A decreased the protein levels of BID, Bcl-xL and PARP while it increased Bax levels. Manu A caused depolarization of the mitochondrial membrane with induction of CHOP, DR4 and DR5. Our results demonstrated that Manu A exerted anticancer effects by inducing apoptosis via inhibition of the Sp1-related signaling pathway in human MPM.

Manumycin A from a new Streptomyces strain induces endoplasmic reticulum stress-mediated cell death through specificity protein 1 signaling in human oral squamous cell carcinoma.

Manumycin A (Manu A) is a natural antibiotic produced by new Streptomyces strain, exhibiting antitumor and anticancer effects. However, the anticancer effects of Manu A on oral squamous cell carcinoma (OSCC) have not been reported. OSCC is an aggressive type of cancer because of its poor prognosis and low survival rate despite advanced medical treatment. We observed that Manu A reduced cell growth and Sp1 protein levels in OSCC cell lines (HN22 and HSC4) in a dose- and time-dependent manner. We also observed downregulation of Sp1 downstream target genes such as p27, p21, Mcl-1 and survivin. Moreover, nuclear staining with DAPI showed that Manu A was able to cause nuclear condensation and further fragmentation. Flow cytometry analyses using Annexin V and propiodium iodide supported Manu A-mediated apoptotic cell death of OSCC cells. Furthermore, Bcl-2 family such as mitochondrial pro­apoptotic Bax, anti-apoptotic Bcl-xl and Bid were regulated by Manu A, triggering the mitochondrial apoptotic pathway. In conclusion, these results indicate that Manu A is a potential to treat human OSCC via cell apoptosis through the downregulation of Sp1.

Role of transcription factor Sp1 in the 4-O-methylhonokiol-mediated apoptotic effect on oral squamous cancer cells and xenograft.

Recently, biphenolic components derived from the Magnolia family have been studied for anti-cancer, anti-stress, and anti-inflammatory pharmacological effects. However, the pharmacological mechanism of action of 4-O-methylhonokiol (MH) is not clear in oral cancer. The aim of this study was to investigate the role of MH in apoptosis and its molecular mechanism in oral squamous cell carcinoma (OSCC) cell lines, HN22 and HSC4, as well as tumor xenografts. Here, we demonstrated that MH decreased cell growth and induced apoptosis in HN22 and HSC4 cells through the regulation of specificity protein 1 (Sp1). We employed several experimental techniques such as MTS assay, DAPI staining, PI staining, Annexin-V/7-ADD staining, RT-PCR, western blot analysis, immunocytochemistry, immunohistochemistry, TUNEL assay and in vivo xenograft model analysis. MH inhibited Sp1 protein expression and reduced Sp1 protein levels via both proteasome-dependent protein degradation and inhibition of protein synthesis in HN22 and HSC4 cells; MH did not alter Sp1 mRNA levels. We found that MH directly binds Sp1 by Sepharose 4B pull-down assay and molecular modeling. In addition, treatment with MH or knocking down Sp1 expression suppressed oral cancer cell colony formation. Moreover, MH treatment effectively inhibited tumor growth and Sp1 levels in BALB/c nude mice bearing HN22 cell xenografts. These results indicated that MH inhibited cell growth, colony formation and also induced apoptosis via Sp1 suppression in OSCC cells and xenograft tumors. Thus, MH is a potent anti-cancer drug candidate for oral cancer.

Licochalcone A induces apoptosis in malignant pleural mesothelioma through downregulation of Sp1 and subsequent activation of mitochondria-related apoptotic pathway.

Licochalcone A (LCA) is a natural product derived from the roots of Glycyrrhiza inflata exhibiting a wide range of bioactivities such as antitumor, anti-oxidant and anti-bacterial effects. Malignant pleural mesothelioma (MPM) is an extremely aggressive type of cancer with a poor prognosis because of its rapid progression. However, LCA has not been investigated concerning its effects on MPM. Preliminarily, we observed that LCA negatively modulated not only cell growth, but also specificity protein 1 (Sp1) expression in MSTO-211H and H28 cell lines. It was found that IC50 values of LCA for growth inhibition of MSTO-211H and H28 cells were approximately 26 and 30 µM, respectively. Consistent with downregulation of Sp1, expression of Sp1 regulatory proteins such as Cyclin D1, Mcl-1 and Survivin was substantially diminished. Mechanistically, LCA triggered the mitochondrial apoptotic pathway by affecting the ratio of mitochondrial proapoptotic Bax to anti-apoptotic Bcl-xL. Bid induced loss of mitochondrial membrane potential, eventually leading to multi-caspase activation and increased sub-G1 population. Moreover, nuclear staining with DAPI highlighted nuclear condensation and fragmentation of apoptotic features. Flow cytometry analyses after staining cells with Annexin V and propiodium iodide corroborated LCA-mediated apoptotic cell death of MPM cells. In conclusion, these results present that LCA may be a potential bioactive material to control human MPM cells by apoptosis via the downregulation of Sp1.

Apoptotic effects of 7,8-dihydroxyflavone in human oral squamous cancer cells through suppression of Sp1.

7,8-Dihydroxyflavone (7,8-DHF) is a member of the flavonoid family and has recently been identified as a brain-derived neurotrophic factor mimetic that selectively activates tropomyosin-receptor kinase B with high affinity. The antioxidant and anticancer effects of 7,8-DHF have been reported. However, the pharmacological mechanisms of 7,8-DHF in oral cancer are unclear. Thus, we investigated the mechanisms of the antiproliferative action of 7,8-DHF on HN22 and HSC4 oral squamous cell carcinoma cell lines. We demonstrated that 7,8-DHF decreased cell growth and induced apoptosis in the HN22 and HSC4 cells through regulation of specificity protein 1 (Sp1) using the MTS assay, DAPI staining, Annexin V, propidium iodide staining, reverse transcription-polymerase chain reaction, immunocytochemistry, pull-down assay and western blot analysis. The results showed that the Sp1 protein bound with 7,8-DHF in the HN22 and HSC4 cells. Taken together, the results suggest that 7,8-DHF could modulate Sp1 transactivation and induce apoptotic cell death by regulating the cell cycle and suppressing antiapoptotic proteins. Furthermore, 7,8-DHF may be valuable for cancer prevention and better clinical outcomes.

Licochalcone A, a natural chalconoid isolated from Glycyrrhiza inflata root, induces apoptosis via Sp1 and Sp1 regulatory proteins in oral squamous cell carcinoma.

Licochalcone A (LCA), a chalconoid derived from root of Glycyrrhiza inflata, has been known to possess a wide range of biological functions such as antitumor, anti-angiogenesis, antiparasitic, anti-oxidant, antibacterial and anti-inflammatory effects. However, the anticancer effects of LCA on oral squamous cell carcinoma (OSCC) have not been reported. Our data showed that LCA inhibited OSCC cell (HN22 and HSC4) growth in a concentration- and time-dependent manner. Mechanistically, it was mediated via downregulation of specificity protein 1 (Sp1) expression and subsequent regulation of Sp1 downstream proteins such as p27, p21, cyclin D1, Mcl-1 and survivin. Here, we found that LCA caused apoptotic cell death in HSC4 and HN22 cells, as characterized by sub-G1 population, nuclear condensation, Annexin V staining, and multi-caspase activity and apoptotic regulatory proteins such as Bax, Bid, Bcl(-xl), caspase-3 and PARP. Consequently, this study strongly suggests that LCA induces apoptotic cell death of OSCC cells via downregulation of Sp1 expression, prompting its potential use for the treatment of human OSCC.