The BLM helicase associates with the telomere structural proteins TRF1 and TRF2 in immortalized cells using the alternative lengthening of telomere (ALT) pathways. This work focuses on identifying protein partners of BLM in cells using ALT. Mass spectrometry and immunoprecipitation techniques have identified three proteins that bind directly to BLM and TRF2 in ALT cells: telomerase-associated protein 1 (TEP1), heat shock protein 90 (HSP90), and topoisomerase II␣ (TOPOII␣). BLM predominantly co-localizes with these proteins in foci actively synthesizing DNA during late S and G 2 /M phases of the cell cycle when ALT is thought to occur. Immunoprecipitation studies also indicate that only HSP90 and TOPOII␣ are components of a specific complex containing BLM, TRF1, and TRF2 but that this complex does not include TEP1. TEP1, TOPOII␣, and HSP90 interact directly with BLM in vitro and modulate its helicase activity on telomere-like DNA substrates but not on nontelomeric substrates. Initial studies suggest that knockdown of BLM in ALT cells reduces average telomere length but does not do so in cells using telomerase. Bloom syndrome (BS)4 is a genetic disease caused by mutation of both copies of the human BLM gene. It is characterized by sun sensitivity, small stature, immunodeficiency, male infertility, and an increased susceptibility to cancer of all sites and types. The high incidence of spontaneous chromosome breakage and other unique chromosomal anomalies in cells from BS patients indicate an increase in homologous recombination in somatic cells (1). Another notable feature of non-immortalized and immortalized cells from BS individuals is the presence of telomeric associations (TAs) between homologous chromosomes (2). Work from our group and others have suggested a role for BLM in recombination-mediated mechanisms of telomere elongation or ALT (alternative lengthening of telomeres), processes that maintain/elongate telomeres in the absence of telomerase (3-5). However, the exact mechanism by which BLM contributes to telomere stability is unknown.Several proteins interact with and regulate BLM helicase activity, including two telomere-specific proteins, TRF1 and TRF2 (6, 7). Although TRF2 stimulates BLM unwinding of telomeric and non-telomeric 3Ј-overhang substrates, TRF1 inhibits BLM unwinding of telomeric substrates. TRF2-mediated stimulation of BLM helicase activity on a telomeric substrate is observed when TRF2 is present in excess or with equimolar amount of TRF1 but not when TRF1 is present in molar excess. Both proteins associate with BLM specifically in ALT cells in vivo, suggesting their involvement in the ALT pathways. In addition to TRF1 and TRF2, the telomere single-strand DNAbinding protein POT1 strongly stimulates BLM helicase activity on long telomeric forked duplexes and D-loop structures (8).Other proteins also play an important role in telomere maintenance in telomerase-negative cells, including RAD50, NBS1, and MRE11, which co-localize with TRF1 and TRF2 in specialized ALT-associated promyelocytic ...

Cells deficient in the recQ-like helicase BLM are characterized by chromosome changes that suggest the disruption of normal mechanisms needed to resolve recombination intermediates and to maintain chromosome stability. Human BLM and topoisomerase IIα interact directly via amino acids 489-587 of BLM and co-localize predominantly in late G2- and M-phases of the cell cycle. Deletion of this region does not affect the inherent in vitro helicase activity of BLM but inhibits the topoisomerase IIα-dependent enhancement of its activity, based on analysis of specific DNA substrates that represent some recombination intermediates. Deletion of the interaction domain from BLM fails to correct the elevated chromosome breakage of transfected BLM-deficient cells. Our results demonstrate that the BLM-topoisomerase IIα interaction is important for preventing chromosome breakage and elucidate a DNA repair mechanism that is critical to maintain chromosome stability in cells and prevent tumor formation.

Study Design Prospective study. Objective To identify proteins with differential expression in the cerebrospinal fluid (CSF) from 15 clinically normal (control) dogs and 15 dogs with cervical spondylomyelopathy (CSM). Summary of Background Data Canine CSM is a spontaneous, chronic, compressive cervical myelopathy similar to human cervical spondylotic myelopathy. There is a limited knowledge of the molecular mechanisms underlying these conditions. Differentially expressed CSF proteins may contribute with novel information about the disease pathogenesis in both dogs and humans. Methods Protein separation was performed with two-dimensional electrophoresis. A Student’s t-test was used to detect significant differences between groups (P < 0.05). Three comparisons were made: 1) control versus CSM-affected dogs, 2) control versus non-corticosteroid treated CSM-affected dogs, and 3) non-corticosteroid treated CSM-affected versus corticosteroid treated CSM-affected dogs. Protein spots exhibiting at least a statistically significant 1.25-fold change between groups were selected for subsequent identification with capillary-liquid chromatography tandem mass spectrometry. Results A total of 96 spots had a significant average change of at least 1.25-fold in one of the three comparisons. Compared to the CSF of control dogs, CSM-affected dogs demonstrated increased CSF expression of eight proteins including vitamin D-binding protein, gelsolin, creatine kinase B-type, angiotensinogen, alpha-2-HS-glycoprotein, SPARC, calsyntenin-1, and complement C3, and decreased expression of pigment epithelium-derived factor, prostaglandin-H2 D-isomerase, apolipoprotein E, and clusterin. In the CSF of CSM-affected dogs, corticosteroid treatment increased the expression of haptoglobin, transthyretin isoform 2, cystatin C-like, apolipoprotein E, and clusterin, and decreased the expression of angiotensinogen, alpha-2-HS-glycoprotein, and gelsolin. Conclusions Many of the differentially expressed proteins are associated with damaged neural tissue, bone turnover, and/or compromised blood-spinal cord barrier. The knowledge of the protein changes that occur in CSM and upon corticosteroid treatment of CSM-affected patients will aid in further understanding the pathomechanisms underlying this disease.

Objectives: Gastrointestinal disorders, such as inflammatory bowel diseases (IBD) and functional gastrointestinal disorders (FGID), involve disrupted homeostatic interactions between the microbiota and the host. Both disorders are worsened during stress, and in laboratory mice, stress exposure has been shown to change the composition of the gut microbiome. Stress-induced changes to the microbiome exacerbate intestinal inflammation and alter intestinal motility in mice.