Menin links the stress response to genome stability in Drosophila melanogaster

Heat Shock Response and Heat Shock Proteins: Current Understanding and Future Opportunities in Human Diseases

The heat shock response is an evolutionarily conserved mechanism that protects cells or organisms from the harmful effects of various stressors such as heat, chemicals toxins, UV radiation, and oxidizing agents. The heat shock response triggers the expression of a specific set of genes and proteins known as heat shock genes/proteins or molecular chaperones, including HSP100, HSP90, HSP70, HSP60, and small HSPs. Heat shock proteins (HSPs) play a crucial role in thermotolerance and aiding in protecting cells from harmful insults of stressors. HSPs are involved in essential cellular functions such as protein folding, eliminating misfolded proteins, apoptosis, and modulating cell signaling. The stress response to various environmental insults has been extensively studied in organisms from prokaryotes to higher organisms. The responses of organisms to various environmental stressors rely on the intensity and threshold of the stress stimuli, which vary among organisms and cellular contexts. Studies on heat shock proteins have primarily focused on HSP70, HSP90, HSP60, small HSPs, and ubiquitin, along with their applications in human biology. The current review highlighted a comprehensive mechanism of heat shock response and explores the function of heat shock proteins in stress management, as well as their potential as therapeutic agents and diagnostic markers for various diseases.

Functional Analysis of a Putative Target of Spatially Varying Selection in the Menin1 Gene of Drosophila melanogaster

While significant effort has been devoted to investigating the potential influence of spatially varying selection on genomic variation, relatively little effort has been devoted to experimental analysis of putative variants or genes experiencing such selection. Previous population genetic work identified an amino acid polymorphism in the Mnn1 gene as one of the most strongly latitudinally differentiated SNPs in the genome of Drosophila melanogaster in the United States and Australia. Here we report the results of our transgenic analysis of this amino acid polymorphism. Genotypes carrying alternative Mnn1 alleles differed in multiple phenotypes in a direction generally consistent with phenotypic differences previously observed along latitudinal clines. These results support inferences from earlier population genomic work that this variant influences fitness, and support the idea that the alleles exhibiting clines may be likely to have pleiotropic effects that are correlated along the axes favored by natural selection.

Animal models of MEN1

Animal models of cancer have been instrumental in advancing our understanding of the biology of tumor initiation and progression, in studying gene function and in performing preclinical studies aimed at testing novel therapies. Several animal models of the MEN1 syndrome have been generated in different organisms by introducing loss-of-function mutations in the orthologues of the human MEN1 gene. In this review, we will discuss MEN1 and MEN1-like models in Drosophila, mice and rats. These model systems with their specific advantages and limitations have contributed to elucidate the function of Menin in tumorigenesis, which turned out to be remarkably conserved from flies to mammals, as well as the biology of the disease. Mouse models of MEN1 closely resemble the human disease in terms of tumor spectrum and associated hormonal changes, although individual tumor frequencies are variable. Rats affected by the MENX (MEN1-like) syndrome share some features with MEN1 patients albeit they bear a germline mutation in Cdkn1b (p27) and not in Men1 Both Men1-knockout mice and MENX rats have been exploited for therapy-response studies testing novel drugs for efficacy against neuroendocrine tumors (NETs) and have provided promising leads for novel therapies. In addition to presenting well-established models of MEN1, we also discuss potential models which, if implemented, might broaden even further our knowledge of neuroendocrine tumorigenesis. In the future, patient-derived xenografts in zebrafish or mice might allow us to expand the tool-box currently available for preclinical studies of MEN1-associated tumors.

dAdd1 and dXNP prevent genome instability by maintaining HP1a localization at Drosophila telomeres

Telomeres are important contributors to genome stability, as they prevent linear chromosome end degradation and contribute to the avoidance of telomeric fusions. An important component of the telomeres is the heterochromatin protein 1a (HP1a). Mutations in Su(var)205, the gene encoding HP1a in Drosophila, result in telomeric fusions, retrotransposon regulation loss and larger telomeres, leading to chromosome instability. Previously, it was found that several proteins physically interact with HP1a, including dXNP and dAdd1 (orthologues to the mammalian ATRX gene). In this study, we found that mutations in the genes encoding the dXNP and dAdd1 proteins affect chromosome stability, causing chromosomal aberrations, including telomeric defects, similar to those observed in Su(var)205 mutants. In somatic cells, we observed that dXNP and dAdd1 participate in the silencing of the telomeric HTT array of retrotransposons, preventing anomalous retrotransposon transcription and integration. Furthermore, the lack of dAdd1 results in the loss of HP1a from the telomeric regions without affecting other chromosomal HP1a binding sites; mutations in dxnp also affected HP1a localization but not at all telomeres, suggesting a specialized role for dAdd1 and dXNP proteins in locating HP1a at the tips of the chromosomes. These results place dAdd1 as an essential regulator of HP1a localization and function in the telomere heterochromatic domain.

Medium from γ-irradiated Escherichia coli bacteria stimulates a unique immune response in Drosophila cells

It is well known that γ-irradiated, non-dividing bacteria can elicit potent immune responses in mammals. Compared to traditional heat or chemical inactivation of microbes, γ-irradiation likely preserves metabolic activity and antigenic features to a larger extent. We have previously shown that antimicrobial peptides are induced in Drosophila by peptidoglycan fragments secreted into the medium of exponentially growing bacterial cultures. In this study, we γ-irradiated Escherichiacoli cells at a dose that halted cell division. The temporal synthesis and release of peptidoglycan fragments were followed as well as the potential of bacterial supernatants to induce immune responses in Drosophila S2 cells. We demonstrate that peptidoglycan synthesis continues for several days post irradiation and that monomeric peptidoglycan is shed into the medium. Whole transcriptome analysis revealed a strong immune response against the bacterial medium. The response to medium taken directly post irradiation shows a large overlap to that of peptidoglycan. Medium from prolonged bacterial incubation does, however, stimulate a selective set of immune genes. A shift towards a stress response was instead observed with a striking induction of several heat shock proteins. Our findings suggest that γ-irradiated bacteria release elicitors that stimulate a novel response in Drosophila.

Loss of menin mediated by endothelial cells treated with CoPP is associated with increased maturation of adipocytes

Oxidative stress is caused by an increase in reactive oxygen species (ROS) relative to the antioxidant defense system. An increase in ROS is known to decrease vascular function, increase inflammatory cytokines, and promote adipocyte hypertrophy. A known regulator of the oxidative stress response is the heat shock protein, heme-oxygenase 1 (HO-1), which is induced by cobalt protoporphyrin IX (CoPP). Menin was recently found to promote the sustained expression of heat shock proteins and is implicated in the regulation of oxidative stress. In this study, we investigated how changes in menin expression affected adipogenesis via the interaction between endothelial cells and adipocytes in response to CoPP treatment during oxidative stress. Using angiotensin II (Ang II) to induce oxidative stress in endothelial cells and adipocytes, we observed the induction of various cytokines including EGF, VEGF, angiogenin, IL-6, and MCP-1. Preadipocytes cultured in endothelial cell conditioned media treated with Ang II showed no changes in differentiation markers. Preadipocytes treated with the endothelial cell-conditioned media pretreated with CoPP resulted in an increase in the number of adipocytes, which expressed higher levels of adipocyte differentiation markers in direct correlation with the complete downregulation of the stress response regulator, menin. This change was not detected in adipocytes directly treated with CoPP alone. Therefore, we concluded that loss of menin is associated with the maturation of adipocytes induced by conditioned media from endothelial cells treated with CoPP.