BRG1 is a prognostic indicator and a potential therapeutic target for prostate cancer.

Brahma-related gene 1 (BRG1) is one of two mutually exclusive ATPases that function as the catalytic subunit of human SWItch/Sucrose NonFermentable (SWI/SNF) chromatin remodeling enzymes. BRG1 has been identified as a tumor suppressor in some cancer types but has been shown to be expressed at elevated levels, relative to normal tissue, in other cancers. Using TCGA (The Cancer Genome Atlas) prostate cancer database, we determined that BRG1 mRNA and protein expression is elevated in prostate tumors relative to normal prostate tissue. Only 3 of 491 (0.6%) sequenced tumors showed amplification of the locus or mutation in the protein coding sequence, arguing against the idea that elevated expression due to amplification or expression of a mutant BRG1 protein is associated with prostate cancer. Kaplan-Meier survival curves showed that BRG1 expression in prostate tumors inversely correlated with survival. However, BRG1 expression did not correlate with Gleason score/International Society of Urological Pathology (ISUP) Grade Group, indicating it is an independent predictor of tumor progression/patient outcome. To experimentally assess BRG1 as a possible therapeutic target, we treated prostate cancer cells with a biologic inhibitor called ADAADi (active DNA-dependent ATPase A Domain inhibitor) that targets the activity of the SNF2 family of ATPases in biochemical assays but showed specificity for BRG1 in prior tissue culture experiments. The inhibitor decreased prostate cancer cell proliferation and induced apoptosis. When directly injected into xenografts established by injection of prostate cancer cells in mouse flanks, the inhibitor decreased tumor growth and increased survival. These results indicate the efficacy of pursuing BRG1 as both an indicator of patient outcome and as a therapeutic target.

Elucidating the mechanism of DNA-dependent ATP hydrolysis mediated by DNA-dependent ATPase A, a member of the SWI2/SNF2 protein family.

The active DNA-dependent ATPase A domain (ADAAD), a member of the SWI2/SNF2 family, has been shown to bind DNA in a structure-specific manner, recognizing DNA molecules possessing double-stranded to single-stranded transition regions leading to ATP hydrolysis. Extending these studies we have delineated the structural requirements of the DNA effector for ADAAD and have shown that the single-stranded and double-stranded regions both contribute to binding affinity while the double-stranded region additionally plays a role in determining the rate of ATP hydrolysis. We have also investigated the mechanism of interaction of DNA and ATP with ADAAD and shown that each can interact independently with ADAAD in the absence of the other. Furthermore, the protein can bind to dsDNA as well as ssDNA molecules. However, the conformation change induced by the ssDNA is different from the conformational change induced by stem-loop DNA (slDNA), thereby providing an explanation for the observed ATP hydrolysis only in the presence of the double-stranded:single-stranded transition (i.e. slDNA).

Altering mammalian transcription networking with ADAADi: An inhibitor of ATP-dependent chromatin remodeling.

Active DNA-dependent ATPase A Domain inhibitor (ADAADi) is the only known inhibitor of ATP-dependent chromatin remodeling proteins that targets the ATPase domain of these proteins. The molecule is synthesized by aminoglycoside phosphotransferase enzyme in the presence of aminoglycosides. ADAADi interacts with ATP-dependent chromatin remodeling proteins through motif Ia present in the conserved helicase domain, and thus, can potentially inhibit all members of this family of proteins. We show that mammalian cells are sensitive to ADAADi but with variable responses in different cell lines. ADAADi can be generated from a wide variety of aminoglycosides; however, cells showed differential response to ADAADi generated from various aminoglycosides. Using HeLa and DU145 cells as model system we have explored the effect of ADAADi on cellular functions. We show that the transcriptional network of a cell type is altered when treated with sub-lethal concentration of ADAADi. Although ADAADi has no known effects on DNA chemical and structural integrity, expression of DNA-damage response genes was altered. The transcripts encoding for the pro-apoptotic proteins were found to be upregulated while the anti-apoptotic genes were found to be downregulated. This was accompanied by increased apoptosis leading us to hypothesize that the ADAADi treatment promotes apoptotic-type of cell death by upregulating the transcription of pro-apoptotic genes. ADAADi also inhibited migration of cells as well as their colony forming ability leading us to conclude that the compound has effective anti-tumor properties.

Context-dependent roles of the Entamoeba histolytica core promoter element GAAC in transcriptional activation and protein complex assembly.

Transcriptional control of the hgl5 gene of Entamoeba histolytica is mediated through an unusual core promoter composed of TATA, GAAC and Initiator elements. In the hgl5 promoter the GAAC element (AATGAACT) determines the site and rate of transcription initiation. Here we tested the role of the GAAC element in transcription activation from upstream regulatory elements (UREs) in the hgl5 promoter. We also examined the function of the GAAC element in the ferredoxin (fdx) promoter and characterized the protein binding to the GAAC element. Electrophoretic mobility shift assays (EMSA) demonstrated that the GAAC region is necessary for higher-order nuclear protein complex assembly. The function of the GAAC element in transcription activation mediated by UREs revealed that mutation of the GAAC element did not affect transcription activation mediated by the hgl5 URE4 but abrogated activation by the hgl5 URE3. We compared the role of the GAAC elements in the hgl5 and fdx promoters. Competitive gel shift assays were consistent with the same nuclear protein binding to the GAAC elements in both genes. Mutation of the GAAC element in the fdx gene decreased reporter gene expression, however, in contrast to hgl5 gene, had no effect on the site of transcription initiation. These results support a role for the GAAC element in assembly of nuclear proteins at the core promoter and in transcription activation mediated by URE3. The differing effect on transcription initiation in the hgl5 and fdx genes upon mutation of the GAAC element suggests a context-dependence of the GAAC-binding protein in gene expression.

Global epigenetic changes induced by SWI2/SNF2 inhibitors characterize neomycin-resistant mammalian cells.

BACKGROUND: Previously, we showed that aminoglycoside phosphotransferases catalyze the formation of a specific inhibitor of the SWI2/SNF2 proteins. Aminoglycoside phosphotransferases, for example neomycin-resistant genes, are used extensively as selection markers in mammalian transfections as well as in transgenic studies. However, introduction of the neomycin-resistant gene is fraught with variability in gene expression. We hypothesized that the introduction of neomycin-resistant genes into mammalian cells results in inactivation of SWI2/SNF2 proteins thereby leading to global epigenetic changes. METHODOLOGY: Using fluorescence spectroscopy we have shown that the inhibitor, known as Active DNA-dependent ATPase ADomain inhibitor (ADAADi), binds to the SWI2/SNF2 proteins in the absence as well as presence of ATP and DNA. This binding occurs via a specific region known as Motif Ia leading to a conformational change in the SWI2/SNF2 proteins that precludes ATP hydrolysis. ADAADi is produced from a plethora of aminoglycosides including G418 and Streptomycin, two commonly used antibiotics in mammalian cell cultures. Mammalian cells are sensitive to ADAADi; however, cells stably transfected with neomycin-resistant genes are refractory to ADAADi. In resistant cells, endogenous SWI2/SNF2 proteins are inactivated which results in altered histone modifications. Microarray data shows that the changes in the epigenome are reflected in altered gene expression. The microarray data was validated using real-time PCR. Finally, we show that the epigenetic changes are quantized. SIGNIFICANCE: The use of neomycin-resistant genes revolutionized mammalian transfections even though questions linger about efficacy. In this study, we have demonstrated that selection of neomycin-resistant cells results in survival of only those cells that have undergone epigenetic changes, and therefore, data obtained using these resistant genes as selection markers need to be cautiously evaluated.

Involvement of a Na+/HCO-3 cotransporter in mouse sperm capacitation.

Mammalian sperm are incapable of fertilizing eggs immediately after ejaculation; they acquire fertilization capacity after residing in the female tract for a finite period of time. The physiological changes sperm undergo in the female reproductive tract that render sperm able to fertilize constitute the phenomenon of "sperm capacitation." We have demonstrated that capacitation is associated with an increase in the tyrosine phosphorylation of a subset of proteins and that these events are regulated by an HCO(3)(-)/cAMP-dependent pathway involving protein kinase A. Capacitation is also accompanied by hyperpolarization of the sperm plasma membrane. Here we present evidence that, in addition to its role in the regulation of adenylyl cyclase, HCO(3)(-) has a role in the regulation of plasma membrane potential in mouse sperm. Addition of HCO(3)(-) but not Cl(-) induces a hyperpolarizing current in mouse sperm plasma membranes. This HCO(3)(-)-dependent hyperpolarization was not observed when Na(+) was replaced by the non-permeant cation choline(+). Replacement of Na(+) by choline(+) also inhibited the capacitation-associated increase in protein tyrosine phosphorylation as well as the zona pellucida-induced acrosome reaction. The lack of an increase in protein tyrosine phosphorylation was overcome by the presence of cAMP agonists in the incubation medium. The lack of a hyperpolarizing HCO(3)(-) current and the inhibition of the capacitation-dependent increase in protein tyrosine phosphorylation in the absence of Na(+) suggest that a Na(+)/HCO(3)(-) cotransporter is present in mouse sperm and is coupled to events regulating capacitation.