CDK-independent role of D-type cyclins in regulating DNA mismatch repair.

Although mismatch repair (MMR) is essential for correcting DNA replication errors, it can also recognize other lesions, such as oxidized bases. In G0 and G1, MMR is kept in check through unknown mechanisms as it is error-prone during these cell cycle phases. We show that in mammalian cells, D-type cyclins are recruited to sites of oxidative DNA damage in a PCNA- and p21-dependent manner. D-type cyclins inhibit the proteasomal degradation of p21, which competes with MMR proteins for binding to PCNA, thereby inhibiting MMR. The ability of D-type cyclins to limit MMR is CDK4- and CDK6-independent and is conserved in G0 and G1. At the G1/S transition, the timely, cullin-RING ubiquitin ligase (CRL)-dependent degradation of D-type cyclins and p21 enables MMR activity to efficiently repair DNA replication errors. Persistent expression of D-type cyclins during S-phase inhibits the binding of MMR proteins to PCNA, increases the mutational burden, and promotes microsatellite instability.

D-type cyclins regulate DNA mismatch repair in the G1 and S phases of the cell cycle, maintaining genome stability.

The large majority of oxidative DNA lesions occurring in the G1 phase of the cell cycle are repaired by base excision repair (BER) rather than mismatch repair (MMR) to avoid long resections that can lead to genomic instability and cell death. However, the molecular mechanisms dictating pathway choice between MMR and BER have remained unknown. Here, we show that, during G1, D-type cyclins are recruited to sites of oxidative DNA damage in a PCNA- and p21-dependent manner. D-type cyclins shield p21 from its two ubiquitin ligases CRL1SKP2 and CRL4CDT2 in a CDK4/6-independent manner. In turn, p21 competes through its PCNA-interacting protein degron with MMR components for their binding to PCNA. This inhibits MMR while not affecting BER. At the G1/S transition, the CRL4AMBRA1-dependent degradation of D-type cyclins renders p21 susceptible to proteolysis. These timely degradation events allow the proper binding of MMR proteins to PCNA, enabling the repair of DNA replication errors. Persistent expression of cyclin D1 during S-phase increases the mutational burden and promotes microsatellite instability. Thus, the expression of D-type cyclins inhibits MMR in G1, whereas their degradation is necessary for proper MMR function in S.

Shexiang Baoxin Pill, a Traditional Chinese Herbal Formula, Rescues the Cognitive Impairments in APP/PS1 Transgenic Mice.

BACKGROUND: Shexiang Baoxin Pill (SBP), a formulated traditional Chinese medicine (TCM), has been widely used to treat cardiovascular diseases for years. This herbal mixture has been shown to promote differentiation of cultured neuronal cells. Here, we aimed to investigate the effects of SBP in attenuating cognitive impairment in APP/PS1 transgenic mice. METHODS: Ethanol and water extracts of SBP, denoted as SBPEtOH and SBPwater, were standardized and applied onto cultured rat pheochromocytoma PC12 cells. The potential effect of SBPEtOH extract in attenuating the cognitive impairments in APP/PS1 transgenic mice was shown by following lines of evidence: (i) inhibition of Aß fibril formation, (ii) suppression of secretions of cytokines, and (iii) improvement of behavioral tests by Morris water maze. RESULTS: SBPwater and SBPEtOH inhibited the formation of ß-amyloid fibrils and protected the Aß-induced cytotoxicity in cultured PC12 cells. In APP/PS1 transgenic mice, the treatment of SBPEtOH inhibited expressions of NO, NOS, AChE, as well as aggregation of Aß. Besides, the levels of pro-inflammatory cytokines were suppressed by SBP treatment in the transgenic mice. Importantly, the behavioral tests by Morris Water maze indicated that SBP attenuated cognitive impairments in APP/PS1 transgenic mice. CONCLUSION: The current result has supported the notion that SPB might ameliorate the cognitive impairment through multiple targets, suggesting that SBP could be considered as a promising anti-AD agent.

Corylin, a flavonoid derived from Psoralea Fructus, induces osteoblastic differentiation via estrogen and Wnt/ß-catenin signaling pathways.

Corylin is a naturally occurring flavonoid isolated from the fruit of Psoralea corylifolia L. (Fabaceae), which is a Chinese medicinal herb in treating osteoporosis. Although a variety of pharmacological activities of corylin have been reported, its osteogenic action and the underlying mechanism in bone development remain unclear. In the present study, the involvement of bone-specific genes in corylininduced differentiated osteoblasts was analyzed by RT-PCR, promoter-reporter assay, and Western blotting. In cultured osteoblasts, corylin-induced cell differentiation and mineralization, as well as increased the expressions of vital biological markers for osteogenesis, such as Runx2, Osterix, Col1, and ALP. Corylin was proposed to have dual pathways in triggering the osteoblastic differentiation. First, the osteogenic function of corylin acted through the activation of Wnt/ß-catenin signaling. The nuclear translocation of ß-catenin of cultured osteoblasts, as determined by flow cytometry and confocal microscopy, was triggered by applied corylin, and which was blocked by DKK-1, an inhibitor of Wnt/ß-catenin signaling. Second, the application of corylin-induced estrogenic response in a dose-dependent manner, and which was blocked by ICI 182 780, an antagonist of estrogen receptor. Furthermore, the activation of Runx2 promoter by corylin was abolished by both DKK-1 and ICI 182,780, indicating that the corylin exhibited its osteogenic effect via estrogen and Wnt/ß-catenin signaling pathways. In addition, corylin regulated the metabolic profiles, as well as the membrane potential of mitochondria, in cultured osteoblasts. Corylin also stimulated the osteogenesis in bone micromass derived from mesenchymal progenitor cells. This study demonstrated the osteogenic activities of corylin in osteoblasts and micromass, suggesting that corylin has the potential to be developed as a novel pro-osteogenic agent in targeting for the treatment of osteoblast-mediated osteoporosis.

Shexiang Baoxin Pill, a Formulated Chinese Herbal Mixture, Induces Neuronal Differentiation of PC12 Cells: A Signaling Triggered by Activation of Protein Kinase A.

Background: Shexiang Baoxin Pill (SBP) is a well-known composite formula of traditional Chinese medicine (TCM), which is commonly used today in treating cardiovascular diseases. SBP consists of seven materials thereof, including Moschus, extract of Ginseng Radix et Rhizoma, Bovis Calculus Artifactus, Cinnamomi Cortex, Styrax, Bufonis Venenum, and Borneolum Syntheticum. Here, we are investigating the potential roles of SBP in inducing neuron differentiation, i.e., seeking possible application in neurodegenerative diseases. Methods: Water and ethanol extracts of SBP, denoted as SBPwater and SBPEtOH, respectively, as well as its individual herbal materials, were standardized and applied onto cultured rat pheochromocytoma PC12 cells. The potential effect of SBP extracts in neuronal differentiation was suggested by following parameters: (i) induction of neurite outgrowth of PC12 cells, (ii) increase of neurofilament expression, and (iii) activation of transcription of neurofilament. Results: The treatments of SBPwater and SBPEtOH, or extracts from individual herbal materials, with or without low concentration of nerve growth factor (NGF), could potentiate the differentiation of cultured PC12 cells. The differentiation was indicated by increase of neurite outgrowth, as well as expression of neurofilaments. In addition, application of H89, a protein kinase A (PKA) inhibitor, suppressed the SBP-induced neurofilament expressions, as well as the phosphorylation of cAMP-responsive element binding protein (CREB) in cultures. Conclusion: SBP is proposed to possess trophic activity in modulating neuronal differentiation of PC12 cells, and this induction is shown to be mediated partly by a cAMP-PKA signaling pathway. These results indicate the neurite-promoting SBP could be useful in developing potential drug in treating or preventing neurodegenerative diseases.

Prenylated Flavonoids from Roots of Glycyrrhiza uralensis Induce Differentiation of B16-F10 Melanoma Cells.

Roots of Glycyrrhiza uralensis have been used as herbal medicine and natural sweetener. By activity-guided phytochemical investigation of the extracts from G.uralensis root, ten flavonoids, namely GF-1⁻GF-10, of which five were prenylated flavonoids, were found to show antiproliferative effects in melanoma B16-F10 cells. Three of the prenylated flavonoids, namely GF-1, GF-4 and GF-9, significantly induced the differentiation of B16-F10 cells; the inductions included increase of tyrosinase activity, tyrosinase protein, and melanin content. In GF-1 and GF-9 induced melanoma differentiation, the phosphorylation of p38 MAPK (mitogen activated potein kinase) was identified; while GF-4 could trigger the phosphorylation of PI3K/AKT (phosphatidylinositol 3-kinase/Protein Kinase B) signaling. However, application of GF-6 to the melanoma cells did not induce differentiation; but which promoted cell apoptotic signaling, i.e., increase levels of cleaved-PRAP, cleaved-caspase 3, and cleaved-caspase 9. These results suggested that different types of prenylated flavonoids from G.uralensis might have potential anticancer effects against melanoma cells by acting through different signaling pathways.

Calycosin orchestrates the functions of Danggui Buxue Tang, a Chinese herbal decoction composing of Astragali Radix and Angelica Sinensis Radix: An evaluation by using calycosin-knock out herbal extract.

ETHNOPHARMACOLOGICAL RELEVANCE: Danggui Buxue Tang (DBT) is a classical Chinese herbal decoction containing two herbs, Astragali Radix (AR) and Angelicae Sinensis Radix (ASR), which serves as dietary supplement for treating women menopausal syndromes. Pharmacological studies indicate that DBT has estrogenic, erythropoietic and osteogenic properties; however, the action mechanism for this complex herbal decoction is not known. Calycosin, a major flavonoid in AR, shares similar structure with ß-estradiol, and thus which is hypothesized to be the critical compound of DBT. Here, we aim to investigate the role of calycosin in DBT in terms of its biological functions by using a calycosin-depleted DBT decoction (DBT(Δcal)). The biological functions of DBT(Δcal) and parental DBT were systematically compared. MATERIALS AND METHODS: In order to standardize DBT decoction, four chemical markers were determined and quantified by HPLC. A semi-preparative HPLC method was utilized to prepare DBT(Δcal). The authenticity of DBT(Δcal) was evaluated by LC-QQQ-MS/MS. To reveal the effect of calycosin on DBT functions, several cell assays related to the known properties of DBT were revealed, including estrogenic, erythropoietic and osteogenic functions. RESULTS: As compared to parental DBT, the estrogenic, erythropoietic and osteogenic abilities were markedly reduced in DBT(Δcal). However, calycosin alone did not show significant responses. CONCLUSIONS: Our results suggest that calycosin is a bioactive chemical in DBT decoction, and which could play a key linker in orchestrating multi-components of DBT as to achieve maximal functions. These discoveries should be invaluable in drug development and in investigating the modernization of traditional Chinese medicine from a new perspective.