Secalonic acid D blocks embryonic palatal mesenchymal cell-cycle by altering the activity of CDK2 and the expression of p21 and cyclin E

Isolation of 4,4'-bond secalonic acid D from the marine-derived fungus Penicillium oxalicum with inhibitory property against hepatocellular carcinoma

4,4'-bond secalonic acid D (4,4'-SAD) is a known compound isolated from the marine-derived fungus Penicillium oxalicum. No study about the antitumor effect of this compound has been reported, except for a few focusing on its bactericidal properties. Herein, we performed an in vitro biology test and found that 4,4'-SAD stimulated the apoptosis of tumor cells in the human hepatocellular carcinoma cell lines PLC/PRF/5 and HuH-7 by activating caspase-3, caspase-8, caspase-9, PARP, p53, and cyclin B1, as well as by regulating the Bax/Bcl-2 ratio. In vivo studies showed that 4,4'-SAD had antitumor efficacy in H22 cell xenograft model. Immunohistochemical analysis revealed that 4,4'-SAD could regulate Bax expression, which is a biomarker of tumor growth. In summary, 4,4'-SAD significantly inhibited tumor growth both in vivo and in vitro.

Identification of a face enhancer reveals direct regulation of LIM homeobox 8 (Lhx8) by wingless-int (WNT)/β-catenin signaling

Development of the mammalian face requires a large number of genes that are expressed with spatio-temporal specificity, and transcriptional regulation mediated by enhancers plays a key role in the precise control of gene expression. Using chromatin immunoprecipitation for a histone marker of active enhancers, we generated a genome-wide map of candidate enhancers from the maxillary arch (primordium for the upper jaw) of mouse embryos. Furthermore, we confirmed multiple novel craniofacial enhancers near the genes implicated in human palate defects through functional assays. We characterized in detail one of the enhancers (Lhx8_enh1) located upstream of Lhx8, a key regulatory gene for craniofacial development. Lhx8_enh1 contained an evolutionarily conserved binding site for lymphoid enhancer factor/T-cell factor family proteins, which mediate the transcriptional regulation by the WNT/β-catenin signaling pathway. We demonstrated in vitro that WNT/β-catenin signaling was indeed essential for the expression of Lhx8 in the maxillary arch cells and that Lhx8_enh1 was a direct target of the WNT/β-catenin pathway. Together, we uncovered a molecular mechanism for the regulation of Lhx8, and we provided valuable resources for further investigation into the gene regulatory network of craniofacial development.

Differential proteomic analysis of HL60 cells treated with secalonic acid F reveals caspase 3-induced cleavage of Rho GDP dissociation inhibitor 2

Secalonic acid F (SAF) has been previously identified, however, little is known about its cytotoxic activity and related cytotoxic mechanism. The aim of this study was to evaluate the cytotoxic activity of SAF isolated from a deep sea originated fungus Penicillium sp. F11 in HL60 cells and to analyze the differences in protein expression of HL60 cells treated with SAF. The CCK-8 assay and Annexin V-FLUOS/PI assay indicated that SAF displayed dose- and time-dependent inhibition of HL60 cell proliferation and induced apoptosis. Two-dimensional gel electrophoresis (2-DE) analysis of HL60 cells treated with SAF (4 µg/ml) revealed 10 differentially expressed protein spots (P<0.05), 5 upregulated and 5 downregulated. Three spots (1 downregulated and 2 upregulated) were identified as Rho GDP dissociation inhibitor 2 (RhoGDI 2) proteins by MALDI-TOF MS. Western blotting further demonstrated the decreased abundance of full-length RhoGDI 2 together with the increased abundance of caspase 3-cleaved product of RhoGDI 2. The caspase 3 inhibitor Ac-DEVD-CHO could suppress the cytotoxic effect of SAF and significantly block the cleavage of RhoGDI 2. RhoGDI 2 is a cytosolic regulator of Rho GTPase and the caspase 3-cleaved product of RhoGDI 2 can advance progression of the apoptotic process. Our data showed that SAF may modulate RhoGDI 2 levels in HL60 cells, thereby potentially disrupting cell signaling pathways important for HL60 cell function.

Role of p21 and cyclin E in normal and secalonic acid D-inhibited proliferation of human embryonic palatal mesenchymal cells

Secalonic acid D (SAD), a cleft palate-inducing teratogen, has been shown to inhibit proliferation/cell cycle progression in association with alteration in the levels of cell cycle regulators, p21 and cyclin E. These studies were conducted to test the hypotheses that p21 and cyclin E play an important functional role in normal human embryonic palatal mesenchymal (HEPM) cell cycle and that their up- and down-regulation, respectively, by SAD is functionally significant to its cell cycle block. Using small interfering RNA (siRNA) to silence p21 gene and transient transfection to overexpress cyclin E in control & SAD-treated HEPM cells, cell proliferation was assessed using a combination of cell numbers, thymidine uptake, CDK2 activity and Ki-67 expression. The results showed that silencing of p21 gene, although increased cell proliferation/numbers and CDK2 activity in normal HEPM cells, failed to counteract SAD-induced anti-proliferative effect despite inducing partial recovery of CDK2 activity. Similar effects were apparent with cyclin E overexpression. It is concluded that p21 and cyclin E are important for normal HEPM cell proliferation. However, SAD-induced deregulation of either protein, singly, may not be sufficient to induce anti-proliferative effect. Involvement of other cell cycle proteins such as cyclin D1 or of multiple proteins in SAD-induced cell cycle block needs to be examined.

Association of genetic polymorphisms in GADD45A, MDM2, and p14 ARF with the risk of chronic benzene poisoning in a Chinese occupational population

Benzene reactive metabolites can lead to DNA damage and trigger the p53-dependent defense responses to maintain genomic stability. We hypothesized that the p53-dependent genes may play a role in the development of chronic benzene poisoning (CBP). In a case-control study of 303 patients with benzene poisoning and 295 workers occupationally exposed to benzene in south China, we investigated associations between the risk of CBP and polymorphisms in three p53-dependent genes. Potential interactions of these polymorphisms with lifestyle factors were also explored. We found p14(ARF) rs3731245 polymorphism was associated with risk of CBP (P=0.014). Compared with those carrying the GG genotype, individuals carrying p14(ARF) rs3731245 GA+AA genotypes had a reduced risk of CBP ([adjusted odds ratio (OR(adj))=0.57, 95%CI=0.36-0.89]. Further analysis showed p14(ARF) TGA/TAG diplotype was associated with an increased risk of CBP (P=0.0006), whereas p14(ARF) TGG/TAA diplotype was associated with a decreased risk of CBP (P=0.0000001). In addition, we found individuals carrying both MDM2 Del1518 WW genotype and p14(ARF) rs3731245 GA+AA genotypes had a lower risk of CBP (OR(adj)=0.25; 95%CI=0.10-0.62; P=0.003). Although these results require confirmation and extension, our findings suggest that genetic polymorphisms in p14(ARF) may have an impact on the risk of CBP in the study population.

PKCδ mediates anti-proliferative, pro-apoptic effects of testosterone on coronary smooth muscle

Sex hormone status has emerged as an important modulator of coronary physiology and cardiovascular disease risk in both males and females. Our previous studies have demonstrated that testosterone increases protein kinase C (PKC) δ expression and activity in coronary smooth muscle (CSMC). Because PKCδ has been implicated in regulation of proliferation and apoptosis in other cell types, we sought to determine if testosterone modulates CSMC proliferation and/or apoptosis through PKCδ. Porcine CSMC cultures (passages 2–6) from castrated males were treated with testosterone for 24 h. Testosterone (20 and 100 nM) decreased [3H]thymidine incorporation in proliferating CSMC to 59 ± 5.3 and 33.1 ± 4.5% of control. Flow cytometric analysis demonstrated that testosterone induced G1arrest in CSMC with a concomitant reduction in the S phase cells. Testosterone reduced protein levels of cyclins D1and E and phosphorylation of retinoblastoma protein while elevating levels of p21cip1and p27kip1. There were no significant differences in the levels of cyclins D3, CDK2, CDK4, or CDK6. Testosterone significantly reduced kinase activity of CDK2 and -6, but not CDK4, -7, or -1. PKCδ small interfering RNA (siRNA) prevented testosterone-mediated G1arrest, p21cip1upregulation, and cyclin D1and E downregulation. Furthermore, testosterone increased CSMC apoptosis in a dose-dependent manner, which was blocked by either PKCδ siRNA or caspase 3 inhibition. These findings demonstrate that the anti-proliferative, pro-apoptotic effects of testosterone on CSMCs are substantially mediated by PKCδ.