Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Mitochondrial Membrane Permeabilization in Cell Death

p53 plays a key role in mediating cell response to various stresses, mainly by inducing or repressing a number of genes involved in cell cycle arrest, senescence, apoptosis, DNA repair, and angiogenesis. According to this important function, p53 activity is controlled in a very complex manner, including several auto-regulatory loops, through the intervention of dozens of modulator proteins (the ‘p53 interactome’). p53 mutations are observed in a significant minority of breast tumours. In the remaining cases, alterations of interactome components or target genes could contribute, to some extent, to reduce the ability of p53 to efficiently manage stress events. While the prognostic and predictive value of p53 is still debated, there is an increasing interest for p53-based therapies. The present paper aims to provide updated information on p53 regulation and function, with specific interest on its role in breast cancer. Endocrine-Related Cancer (2006) 13 293–325

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p53 and breast cancer, an update

Nuclear receptor (NR) coregulators (coactivators and corepressors) are essential elements in regulating nuclear receptor-mediated transcription. In a little more than a decade since their discovery, these proteins have been studied mechanistically and reveal that the regulation of transcription is a highly controlled and complex process. Because of their central role in regulating NR-mediated transcription and in coordinating intercompartmental metabolic processes, disruptions in coregulator biology can lead to pathological states. To date, the extent to which they are involved in human disease has not been widely appreciated. In a complete literature survey, we have identified nearly 300 distinct coregulators, revealing that a great variety of enzymatic and regulatory capabilities exist for NRs to regulate transcription and other cellular events. Here, we substantiate that coregulators are broadly implicated in human pathological states and will be of growing future interest in clinical medicine.

/pdf/nuclear-receptor-coregulators-and-human-disease-2fus8uh67e.pdf

Nuclear receptor coregulators and human disease.

The Growth Arrest and DNA Damage-inducible 45 (GADD45) proteins have been implicated in regulation of many cellular functions including DNA repair, cell cycle control, senescence and genotoxic stress. However, the pro-apoptotic activities have also positioned GADD45 as an essential player in oncogenesis. Emerging functional evidence implies that GADD45 proteins serve as tumor suppressors in response to diverse stimuli, connecting multiple cell signaling modules. Defects in the GADD45 pathway can be related to the initiation and progression of malignancies. Moreover, induction of GADD45 expression is an essential step for mediating anti-cancer activity of multiple chemotherapeutic drugs and the absence of GADD45 might abrogate their effects in cancer cells. In this review, we present a comprehensive discussion of the functions of GADD45 proteins, linking their regulation to effectors of cell cycle arrest, DNA repair and apoptosis. The ramifications regarding their roles as essential and central players in tumor growth suppression are also examined. We also extensively review recent literature to clarify how different chemotherapeutic drugs induce GADD45 gene expression and how its up-regulation and interaction with different molecular partners may benefit cancer chemotherapy and facilitate novel drug discovery.

GADD45 Proteins: Central Players in Tumorigenesis

Proc Amer Assoc Cancer Res, Volume 47, 2006

1623 

To identify novel methylation-silenced genes in gastric cancers, we here performed a chemical genomic screening, a genome-wide search for genes up-regulated by treatment with a demethylating agent, 5-aza-2’-deoxycytidine (5-aza-dC). After treatment of a gastric cancer cell line, AGS, with 5-aza-dC at 1 μM, 579 genes were up-regulated at 16-fold or more, using an oligonucleotide microarray with 39,000 genes. From these genes, we selected 44 known genes on autosomes whose silencing in gastric cancer has not been reported. Thirty-two of them had CpG islands (CGIs) in their putative promoter regions, and the CGIs of all the 32 genes were found to be methylated in AGS by methylation-specific PCR. Analysis of 5 additional gastric cancer cell lines (MKN28, MKN45, HSC44, HSC57, KATOIII) showed that 27 genes were methylated in multiple gastric cancer cell lines. AGS cell line was expected to have 421 ± 75 (95 % confidence interval) methylation-silenced genes. Additionally, we analyzed methylation statuses of 16 potential tumor-related genes with promoter CGIs and up-regulation of 4-fold or more, and 14 of them were methylated in AGS. Methylation statuses of the 32 randomly selected and 16 potential tumor-related genes were analyzed in 10 primary gastric cancers, and 42 genes ( ABHD9 , ADFP , ALDH1A3 , ANXA5 , AREG , BDNF , BMP7 , CAV1 , CDH2 , CLDN3 , CTSL , EEF1A2 , F2R , FADS1 , FSD1 , FST , FYN , GPR54 , GREM1 , IGFBP3 , IGFBP7 , IRS2 , KISS1 , MARK1 , MLF1 , MSX1 , MTSS1 , NT5E , PAX6 , PLAGL1 , PLAU , PPIC , RBP4 , RORA , SCRN1 , TBX3 , TFAP2C , TNFSF9 , ULBP2 , WIF1 , ZNF177 , and ZNF559 ) were methylated in at least one primary gastric cancer. Although some of these genes could be causally related to development and progression of gastric cancers, it was likely that the majority do not have such roles, considering the large number of methylation-silenced genes. Therefore, potential tumor-related genes were selected based upon their known functions, chromosomal locations, methylation in primary samples, and expression in normal gastric mucosae. MTSS1/MIM/BEG4 (8q22) met all these criteria, and was a good candidate for a tumor-related gene. The usefulness of chemical genomic screening was also confirmed.

A chemical genomic screening for methylation-silenced genes in gastric cancer cell lines using 5-aza-2’-deoxycytidine treatment and oligonucleotide microarray

Treatment of the breast cancer cell line, MDAMB468 with the DNA methylation inhibitor, 5-azacytidine (5-AzaC) results in growth arrest, whereas the growth of the normal breast epithelial line DU99 (telomerase immortalized) is relatively unaffected. Comparing gene expression profiles of these two lines after 5-AzaC treatment, we identified 36 genes that had relatively low basal levels in MDAMB468 cells compared to the DU99 line and were induced in the cancer cell line but not in the normal breast epithelial line. Of these genes, 33 have associated CpG islands greater than 300 bp in length but only three have been previously described as targets for aberrant methylation in human cancer. Northern blotting for five of these genes (alpha-Catenin, DTR, FYN, GADD45a, and Zyxin) verified the array results. Further analysis of one of these genes, GADD45a, showed that 5-AzaC induced expression in five additional breast cancer cell lines with little or no induction in three additional lines derived from normal breast epithelial cells. The CpG island associated with GADD45a was analysed by bisulfite sequencing, sampling over 100 CpG dinucleotides. We found that four CpG's, located approximately 700 bp upstream of the transcriptional start site are methylated in the majority of breast cancer cell lines and primary tumors but not in DNA from normal breast epithelia or matched lymphocytes from cancer patients. Therefore, this simple method of dynamic transcriptional profiling yielded a series of novel methylation-sensitive genes in breast cancer including the BRCA1 and p53 responsive gene, GADD45a.

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Analysis of methylation-sensitive transcriptome identifies GADD45a as a frequently methylated gene in breast cancer.

Pollen serves as an essential protein source for honey bee larvae. The nutrients in pollen greatly influence larval growth and development. Here, the survival, prepupal weight, developmental stage, pollen digestibility and midgut cells in honey bee (Apis mellifera L.) larvae were evaluated by performing in vitro and 5-ethynyl-2′-deoxyuridine (EdU) assays on larvae reared on three single pollens (Brassica napus L., Armeniaca sibirica L., and Pyrus bretschneideri Rehd.) and a pollen mixture (mixture of the three pollens in equal proportions). The results showed that the survival rate of larvae fed 10 mg of rape pollen was lowest (P < 0.05), but there were no notable differences in the survival rate among the groups receiving the other types and doses of pollen (P > 0.05). The prepupal weight of larvae fed apricot pollen was significantly lower than those of the other groups (P < 0.05). The digestibility of rape pollen and the pollen mixture were dramatically higher than those of apricot and pear pollen (P < 0.05). Pear and mixed pollen exerted negative effects on the nuclear area of midgut cells in the early larval stage (P < 0.05). In conclusion, detection of larval midgut cells using the EdU assay might be an effective method to assess the pollen nutritive value in honey bees. Compared to apricot and pear pollen, rape pollen was more beneficial in larval honey bee growth and development.

Effects of Three Types of Pollen on the Growth and Development of Honey Bee Larvae (Hymenoptera, Apidae)

Tissue phenotypic plasticity facilitates rapid adaptation of organisms to biotic and/or abiotic pressure. The reproductive capacity of honey bee workers (Apis mellifera) is plastic and responsive to pheromones produced by broods and the queen. Egg laying workers (ELWs), which could reactivate their ovaries and lay haploid eggs upon queen lost, have been commonly discussed from many aspects. However, it remains unclear whether midgut homeostasis in ELWs is affected during plastic changes. Here, we found that the expression of nutrition- and autophagy-related genes was up-regulated in the midguts of ELWs, compared with that in nurse workers (NWs) by RNA-sequencing. Furthermore, the area and number of autophagosomes were increased, along with significantly increased cell death in the midguts of ELWs. Moreover, cell cycle progression in the midguts of ELWs was increased compared with that in NWs. Consistent with the up-regulation of nutrition-related genes, the body and midgut sizes, and the number of intestinal proliferation cells of larvae reared with royal jelly (RJ) obviously increased more than those reared without RJ in vitro. Finally, cell proliferation was dramatically suppressed in the midguts of ELWs when autophagy was inhibited. Altogether, our data suggested that autophagy was induced and required to sustain cell proliferation in ELWs’ midguts, thereby revealing the critical role of autophagy played in the intestines during phenotypic plasticity changes.

/pdf/autophagy-is-required-to-sustain-increased-intestinal-cell-1o82v4iy.pdf

Yueqi Guo

Papers

Analysis of methylation-sensitive transcriptome identifies GADD45a as a frequently methylated gene in breast cancer.

Effects of Three Types of Pollen on the Growth and Development of Honey Bee Larvae (Hymenoptera, Apidae)

Autophagy Is Required to Sustain Increased Intestinal Cell Proliferation during Phenotypic Plasticity Changes in Honey Bee (Apis mellifera)

A review of factors influencing diapause in bumble bee queens