Optimizing outcomes with azacitidine: recommendations from Canadian centres of excellence.

Myelodysplastic syndromes (mdss) constitute a heterogeneous group of malignant hematologic disorders characterized by marrow dysplasia, ineffective hematopoiesis, peripheral blood cytopenias, and pronounced risk of progression to acute myeloid leukemia. Azacitidine has emerged as an important treatment option and is recommended by the Canadian Consortium on Evidence-Based Care in mds as a first-line therapy for intermediate-2 and high-risk patients not eligible for allogeneic stem cell transplant; however, practical guidance on how to manage patients through treatment is limited. This best practice guideline provides recommendations by a panel of experts from Canadian centres of excellence on the selection and clinical management of mds patients with azacitidine. Familiarity with the referral process, treatment protocols, dose scheduling, treatment expectations, response monitoring, management of treatment breaks and adverse events, and multidisciplinary strategies for patient support will improve the opportunity for optimizing treatment outcomes with azacitidine.

Long-term remission after autologous stem-cell transplantation for relapsed histiocytic sarcoma.

Histiocytic sarcoma is diagnosed according to established criteria. However, treatment is controversial: although lymphoma chemotherapy regimens are often used, their impact on the natural history of the disease is unclear. Here, we report a disease-free survival of 2 years after autologous stem-cell transplantation in a patient with relapsed histiocytic sarcoma.

Heterodimerization of mineralocorticoid and glucocorticoid receptors at a novel negative response element of the 5-HT1A receptor gene.

Negative regulation of neuronal serotonin (5-HT1A) receptor levels by glucocorticoids in vivo may contribute to depression. Both types I (mineralocorticoid) and II (glucocorticoid) receptors (MR and GR, respectively) participate in corticosteroid-induced transcriptional repression of the 5-HT1A gene; however, the precise mechanism is unclear. A direct repeat 6-base pair glucocorticoid response element (GRE) half-site 5'-TGTCCT separated by 6 nucleotides was conserved in human, mouse, and rat 5-HT1A receptor promoters. In SN-48 neuronal cells that express MR, GR, and 5-HT1A receptors, deletion or inactivation of the nGRE (negative GRE) eliminated negative regulation of the rat 5-HT1A or heterologous promoters by corticosteroids, whereas its inclusion conferred corticosteroid-induced inhibition to a heterologous promoter. Bacterially expressed recombinant MR and GR preferentially bound to the nGRE as a heterodimer, as identified in nuclear extracts of MR/GR-transfected COS-7 cells, and with higher affinity than MR or GR homodimers. In SN48 and COS-7 cells, concentration-dependent coactivation of MR and GR was required for maximal inhibitory action by corticosteroids and was abrogated in the L501P-GR mutant lacking DNA binding activity. Corticosteroid-mediated transcriptional inhibition was greater for MR/GR in combination than for MR or GR alone. These data represent the first identification of an nMRE/GRE and indicate that heterodimerization of MR and GR mediates direct corticosteroid-induced transrepression of the 5-HT1A receptor promoter.

Transcriptional mechanisms for induction of 5-HT1A receptor mRNA and protein in activated B and T lymphocytes.

Serotonin (5-HT) up-regulates B and T lymphocyte proliferation by activating mitogen-induced cell surface 5-HT(1A) receptors. The mechanism of 5-HT(1A) receptor induction by B and T cell mitogens at the mRNA and protein levels in mouse splenocytes was addressed. Quantitation by RNase protection assay showed maximal increases of 3.4-, 3.0-, 3.8-, and 4.9-fold in relative 5-HT(1A) mRNA levels after 48 h of stimulation of splenocytes with lipopolysaccharide, phytohemagglutinin, concanavalin A, or phorbol 12-myristate 13-acetate plus ionomycin, respectively, as compared with unstimulated cells. Mitogens did not alter 5-HT(1A) mRNA stability (t(12) = 26 h), but induction of 5-HT(1A) mRNA was blocked by the transcriptional inhibitor actinomycin D (10 microgram/ml) and by inhibition of nuclear factor-kappaB signaling. Additionally, mitogenic stimulation of transcription was paralleled by increased cell surface 5-HT(1A) receptor immunoreactivity in splenocytes. Thus, mitogen-induced 5-HT(1A) receptor expression appears to involve transcriptional regulation by the nuclear factor-kappaB signaling cascade. Increased expression of the 5-HT(1A) receptor in activated B and T lymphocytes may enhance the immune response and provide therapeutic target for tissue inflammation and immune stimulation.

Novel dual repressor elements for neuronal cell-specific transcription of the rat 5-HT1A receptor gene.

The level of expression of the 5-HT1A receptor in the raphe and limbic systems is implicated in the etiology and treatment of major depression and anxiety disorders. The rat 5-HT1A receptor gene is regulated by a proximal TATA-driven promoter and by upstream repressors that inhibit gene expression. Deletion of a 71-base pair (bp) segment between -1590/-1519 bp of the 5-HT1A receptor gene induced over 10-fold enhancement of transcriptional activity in both 5-HT1A receptor-expressing (RN46A raphe and SN48 septal) cells and receptor-negative (L6 myoblast and C6 glioma) cells. A 31-bp segment of the repressor was protected from DNase I digestion by RN46A or L6 nuclear extracts. Within the 31-bp segment, a single protein complex was present in receptor-expressing cells that bound a novel 14-bp DNA element; in receptor-negative cells, an additional complex bound an adjacent 12-bp sequence. In receptor-positive but not receptor-negative cells, mutation of the 14-bp element to eliminate protein binding abrogated repression to nearly the same extent as deletion of the -1590/-1519 bp segment. Additional mutation of both 14-bp and 12-bp elements abolished protein binding and repressor activity in receptor-negative cells. Thus a single protein-DNA complex at the 14-bp element represses the 5-HT1A receptor gene in 5-HT1A receptor-positive neuronal cells, whereas adjacent DNA elements provide a dual repression mechanism in 5-HT1A receptor-negative cells.

TATA-driven transcriptional initiation and regulation of the rat serotonin 5-HT1A receptor gene.

The transcriptional initiation and regulation of the rat serotonin 5-HT1A receptor gene were characterized. By three types of analyses, a single brain-specific site of transcriptional initiation was localized to -967 bp upstream of the translation initiation codon that is utilized both in hippocampus and in the rat raphe RN46A cell line. This major site of transcriptional initiation was located 58 bp downstream from a consensus TATA element, suggesting TATA-driven transcription of the rat 5-HT1A receptor. To identify the promoter activity of the receptor gene, progressive 5' deletions of the -2,719/-117-bp fragment of the 5-HT1A promoter linked to luciferase gene were transfected into 5-HT1A-negative (pituitary GH4C1, L6 myoblast, and C6 glioma) and 5-HT1A-positive (septal SN-48 and raphe RN46A) cell lines. Enhancer regions were identified within a fragment between nucleotides -426 and -117 that selectively enhanced transcription in 5-HT1A-positive cells. A nonselective enhancer/promoter that mediated expression in all cell lines was located upstream between -1,519 and -426 bp in a DNA segment containing consensus TATA, CCAAT, SP-1, and AP-1 elements as well as a poly-GT26 dinucleotide repeat. Strong repression of transcription in all cell lines was conferred by the region upstream of -1,519 bp that contains a 152-bp DNA segment with >80% identity to RANTES, tumor necrosis factor-beta, and other immune system genes. Our results indicate that TATA-driven expression of the 5-HT1A receptor is regulated by a novel proximal tissue-specific enhancer region, a nonselective promoter, and an upstream repressor region that is distinct from previously identified neuron-specific repressors.

A putative alpha-helical G beta gamma-coupling domain in the second intracellular loop of the 5-HT1A receptor.

We have identified a conserved threonine residue in the second intracellular (i2) loop of the 5-HT1A receptor that when mutated to alanine prevents coupling to G beta gamma-mediated signaling, while preserving G alpha i-induced actions. In this review, we investigate the characteristics and potential role of the i2 domain in the coupling of the 5-HT1A receptor and other receptors to G proteins. The i2 domain, as well as portions of the i3 domain, is predicted to form an amphipathic alpha-helix with a positively charged face and a hydrophobic face. Mutagenesis experiments support a model in which the hydrophobic faces of these alpha-helical domains form an intracellular binding "pocket" for interaction with G proteins. Embedded in the hydrophobic face, Thr 149 is crucial for signaling through G beta gamma subunits, perhaps via interaction with its hydroxyl side-chain. Mutation of other residues of the i2 domain of Gi-coupled receptors is required to substantiate the importance of the alpha-helical i2 domain in receptor-G beta gamma signaling. If confirmed in other receptors, these results support a general model in which activated receptor and G beta gamma subunits remain associated to interact with effectors in a receptor-specific manner.

The 5-HT1A receptor: signaling, desensitization, and gene transcription.

The hypothesis that antianxiety or antidepressant agents (e.g., 5-HT1A agonists, 5-HT uptake blockers) exert their clinical actions via enhancement of serotonergic neurotransmission due to desensitization of 5-HT1A autoreceptors predicts that regulation of this receptor plays a crucial role in the therapeutic actions of these agents. A multidisciplinary strategy is described for the characterization of the 5-HT1A receptor at the level of cellular signaling mechanisms and genetic regulation, using heterologous expression of the cloned receptor in cell lines, site-directed mutagenesis, isolation of receptor-positive neuronal cell lines, and promoter analysis of the 5-HT1A receptor gene. These analyses will yield new insights into the possible mechanisms down-regulation of 5-HT1A receptor signaling, and may suggest novel sites of inherent defect involved in anxiety syndromes or major depression.