Akt: A Double-Edged Sword in Cell Proliferation and Genome Stability

The Akt family of serine/threonine protein kinases are key regulators of multiple aspects of cell behaviour, including proliferation, survival, metabolism, and tumorigenesis. Growth-factor-activated Akt signalling promotes progression through normal, unperturbed cell cycles by acting on diverse downstream factors involved in controlling the G1/S and G2/M transitions. Remarkably, several recent studies have also implicated Akt in modulating DNA damage responses and genome stability. High Akt activity can suppress ATR/Chk1 signalling and homologous recombination repair (HRR) via direct phosphorylation of Chk1 or TopBP1 or, indirectly, by inhibiting recruitment of double-strand break (DSB) resection factors, such as RPA, Brca1, and Rad51, to sites of damage. Loss of checkpoint and/or HRR proficiency is therefore a potential cause of genomic instability in tumor cells with high Akt. Conversely, Akt is activated by DNA double-strand breaks (DSBs) in a DNA-PK- or ATM/ATR-dependent manner and in some circumstances can contribute to radioresistance by stimulating DNA repair by nonhomologous end joining (NHEJ). Akt therefore modifies both the response to and repair of genotoxic damage in complex ways that are likely to have important consequences for the therapy of tumors with deregulation of the PI3K-Akt-PTEN pathway

MiR-143 enhances adipogenic differentiation of 3T3-L1 cells through targeting the coding region of mouse pleiotrophin

AbstractAdipogenic differentiation of preadipocytes is a complex process regulated by various factors including miRNAs and cytokines. MiR-143 is a well known miRNA that enhances adipogenesis. Pleiotrophin (PTN), a heparin-binding growth factor, plays a negative role in adipogenesis. In this investigation, we demonstrate that PTN is a target gene of miR-143 during adipogenic differentiation in 3T3-L1 preadipocytes. MiR-143 down regulates PTN expression through interaction with a target site of miR-143 in the coding region of mouse PTN. The rare codons upstream of the target site regulate miR143-induced translational knockdown of PTN, which provides more insight into the mechanism of adipogenic differentiation

Regulation of the metaphase-anaphase transition in mitosis in mammalian cells

A key step in mitosis is the separation of sister chromatids at the metaphase-anaphase transition, this step is controlled by the anaphase-promoting complex (APC) and it's regulatory proteins. On the other hand, several earlier studies showed that Ca2+ signaling is involved in regulating the metaphase-anaphase transition in meiosis. The present study is aimed at investigating the signaling transduction pathway in regulating the metaphase-anaphase transition in mitosis in mammalian cells. We tried to answer three questions: ( 1 ) Is Cdk1 inactivation required for the metaphase-anaphase transition in mammalian cells? (2) Is calcium signaling required for the activation of APC in mitosis in mammalian somatic cells? (3) How does calcium signaling play its role in mitosis? Using a GFP gene fusion technique and living cell imaging methods, we have conducted a series of experiments to answer those key questions. First, we measured the temporal and spatial dependent proteolysis of both securin and cyclin B and found that both of them are degraded before the onset of anaphase. By quantify the protein level of nondegradable cyclin B (Δ85) compared with endogenous cyclin B, we found that a low level of nondegradable cyclin B can cause cells arrested before M/A transition. These results indicate that Cdk1 inactivation is required for sister chromatids separation. Second, by examining the differential effects of Ca2+ signaling blockers (BAPTA/AM, BAPTA, KN-93, heparin) on the metaphase-anaphase transition in HeLa cells, we found that the activation of APC depends on Ca2+ signaling via Ca2+/CaM-dependent protein kinase II (CaMKII). The inhibition of APC by Ca2+ signal blockers may have two parallel pathways, one is through the spindle checkpoint via the destruction of mitotic spindle, while the another is suppression of CaMKII activity. Finally, we examined other important signaling molecules involved in the metaphase-anaphase transition, Mad2, Mad1 and Polo-like kinase 1. By measuring the dynamics of Mad2/Mad1 and cyclin B proteolysis in intact living cells, we demonstrated the degradation of cyclin B is related to the translocation of Mad2/Mad1. The detailed molecular mechanisms of the signaling transduction pathway in the metaphase-anaphase transition in mitosis mammalian cells were discussed

Different thresholds of MPF inactivation are responsible for controlling different mitotic events in mammalian cell division

We present evidence for a paradigm that, during cell division, the decreasing activity of MPF acts as a master signal, which utilizes different thresholds to control the initiation of different mitotic events. The key temporal control here is the degradation of cyclin B1. Using single cell analysis, we measured the kinetics of cyclin B1 degradation and determined quantitatively the thresholds of cyclin B1 level for different mitotic events within a HeLa cell. These observed thresholds were: 1.36 +/- 0.49 mu M ( for chromosome separation), 0.75 +/- 0.08 mu M ( for cytokinesis) and 0.54 +/- 0.16 mu M ( for nuclear reassembly). By comparison, the average concentration of endogenous cyclin B1 within a prometaphase cell was found to be 2.92 +/- 1.7 mu M. We suggest that the decreasing order of these thresholds plays an important role in triggering the initiation of successive mitotic events in cell division

Application of proteomics to determine the mechanism of action of traditional Chinese medicine remedies

AbstractEthnopharmacological relevanceThe rationale for using traditional Chinese medicine (TCM) is based on the experience that has been gained from its wide use over thousands of years. However, the mechanisms of action of many TCM are still unclear. Proteomics, which mainly characterizes protein functions, protein–protein interactions, and protein modification in tissues or animals, can be used to investigate signaling pathway perturbations in cells or the whole body. Proteomics has improved the discovery process of effective TCM compounds, and has helped to elucidate their possible mechanisms of action. Therefore, a systematic review of the application of proteomics on TCM research is of great importance and necessity. This review strives to describe the literature on the application of proteomics to elucidate the mechanism of action of TCM on various diseases, and provide the essential discussion on the further utilization of proteomics data to accelerate TCM research.Materials and methodsLiterature survey was performed via electronic search on Pubmed with keywords ‘Proteomics’ and ‘Traditional Chinese Medicine’. The papers written in English were acquired and analyzed in this review.ResultsThis review mainly summarizes the application of proteomics to investigate TCM remedies for neuronal disease, cancer, cardiovascular disease, diabetes, and immunology-related disease.ConclusionsResearchers have applied proteomics to study the mechanism of action of TCM and made substantial progresses. Further studies are required to determine the protein targets of the active compounds, analyze the mechanism of actions in patients, compare the clinical effects with western medicine

CDK1 switches mitotic arrest to apoptosis by phosphorylating Bcl-2/Bax family proteins during treatment with microtubule interfering agents

Microtubule interfering agents (MIAs), that can stabilise or depolymerise microtubules, are an important class of cancer chemotherapeutic drugs. They can lead to mitotic arrest and subsequent apoptosis. We demonstrate that cell cycle-dependent kinase 1 (CDK1) is important in switching cells from mitotic arrest to apoptosis during MIAs treatment. Overexpression of non-degradable cyclin B1 sustained CDK1 activation and mitotic arrest, followed by caspase-3 dependent apoptosis. CDK1 is responsible for the phosphorylation of several pro- and anti-apoptotic Bcl-2 family proteins during MIAs treatment. CDK1-mediated Bcl-2 serine 70 phosphorylation enhances its pro-apoptotic function, whereas CDK1-mediated Bad serine 128 phosphorylation promotes apoptosis. Blockage of CDK1 activity with a specific pharmacological inhibitor suppresses Mcl-1 phosphorylation, degradation and its anti-apoptotic function. Therefore, the death of cancer cells under MIAs treatment was caused by imbalance between CDK1-induced alterations in the pro-apoptotic and anti-apoptotic functions of phosphorylated Bcl-2 family proteins

Upregulation of the APOBEC3 Family Is Associated with a Poor Prognosis and Influences Treatment Response to Raf Inhibitors in Low Grade Glioma

Apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) has been identified as a group of enzymes that catalyze cytosine deamination in single-stranded (ss) DNA to form uracil, causing somatic mutations in some cancers. We analyzed the APOBEC3 family in 33 TCGA cancer types and the results indicated that APOBEC3s are upregulated in multiple cancers and strongly correlate with prognosis, particularly in low grade glioma (LGG). Then we constructed a prognostic model based on family expression in LGG where the APOBEC3 family signature is an accurate predictive model (AUC of 0.85). Gene mutation, copy number variation (CNV), and a differential gene expression (DEG) analysis were performed in different risk groups, and the weighted gene co-expression network analysis (WGCNA) was employed to clarify the role of various members in LGG; CIBERSORT algorithm was deployed to evaluate the landscape of LGG immune infiltration. We found that upregulation of the APOBEC3 family expression can strengthen Ras/MAPK signaling pathway, promote tumor progression, and ultimately reduce the treatment benefits of Raf inhibitors. Moreover, the APOBEC3 family was shown to enhance the immune response mediated by myeloid cells and interferon gamma, as well as PD-L1 and PD-L2 expression, implying that they have immunotherapy potential. Therefore, the APOBEC3 signature enables an efficient assessment of LGG patient survival outcomes and expansion of clinical benefits by selecting appropriate individualized treatment strategies