Leukemia translocation protein PLZF inhibits cell growth and expression of cyclin A.
(1/2427)
The PLZF gene was identified by its fusion with the RARalpha locus in a therapy resistant form of acute promyelocytic leukemia (APL) associated with the t(11;17)(q23;q21) translocation. Here we describe PLZF as a negative regulator of cell cycle progression ultimately leading to growth suppression. PLZF can bind and repress the cyclin A2 promoter while expression of cyclin A2 reverts the growth suppressed phenotype of myeloid cells expressing PLZF. In contrast RARalpha-PLZF, a fusion protein generated in t(11;17)(q23;q21)-APL activates cyclin A2 transcription and allows expression of cyclin A in anchorage-deprived NIH3T3 cells. Therefore, cyclin A2 is a candidate target gene for PLZF and inhibition of cyclin A expression may contribute to the growth suppressive properties of PLZF. Deregulation of cyclin A2 by RARalpha-PLZF may represent an oncogenic mechanism of this chimeric protein and contribute to the aggressive clinical phenotype of t(11;17)(q23;q21)-associated APL. (+info)
Retinoic acid, but not arsenic trioxide, degrades the PLZF/RARalpha fusion protein, without inducing terminal differentiation or apoptosis, in a RA-therapy resistant t(11;17)(q23;q21) APL patient.
(2/2427)
Primary blasts of a t(11;17)(q23;q21) acute promyelocytic leukaemia (APL) patient were analysed with respect to retinoic acid (RA) and arsenic trioxide (As2O3) sensitivity as well as PLZF/RARalpha status. Although RA induced partial monocytic differentiation ex vivo, but not in vivo, As203 failed to induce apoptosis in culture, contrasting with t(15;17) APL and arguing against the clinical use of As203 in t(11;17)(q23;q21) APL. Prior to cell culture, PLZF/RARalpha was found to exactly co-localize with PML onto PML nuclear bodies. However upon cell culture, it quickly shifted towards microspeckles, its localization found in transfection experiments. Arsenic trioxide, known to induce aggregation of PML nuclear bodies, left the microspeckled PLZF/RARalpha localization completely unaffected. RA treatment led to PLZF/RARalpha degradation. However, this complete PLZF/RARalpha degradation was not accompanied by differentiation or apoptosis, which could suggest a contribution of the reciprocal RARalpha/PLZF fusion product in leukaemogenesis or the existence of irreversible changes induced by the chimera. (+info)
RFLAT-1: a new zinc finger transcription factor that activates RANTES gene expression in T lymphocytes.
(3/2427)
RANTES (Regulated upon Activation, Normal T cell Expressed and Secreted) is a chemoattractant cytokine (chemokine) important in the generation of inflammatory infiltrate and human immunodeficiency virus entry into immune cells. RANTES is expressed late (3-5 days) after activation in T lymphocytes. Using expression cloning, we identified the first "late" T lymphocyte associated transcription factor and named it "RANTES Factor of Late Activated T Lymphocytes-1" (RFLAT-1). RFLAT-1 is a novel, phosphorylated, zinc finger transcription factor that is expressed in T cells 3 days after activation, coincident with RANTES expression. While Rel proteins play the dominant role in RANTES gene expression in fibroblasts, RFLAT-1 is a strong transactivator for RANTES in T cells. (+info)
Comparative synteny cloning of zebrafish you-too: mutations in the Hedgehog target gli2 affect ventral forebrain patterning.
(4/2427)
Zebrafish you-too (yot) mutations interfere with Hedgehog (Hh) signaling during embryogenesis. Using a comparative synteny approach, we isolated yot as a zinc finger transcription factor homologous to the Hh target gli2. Two alleles of yot contain nonsense mutations resulting in carboxy-terminally truncated proteins. In addition to causing defects in midline development, muscle differentiation, and retinal axon guidance, yot mutations disrupt anterior pituitary and ventral forebrain differentiation. yot mutations also cause ectopic lens formation in the ventral diencephalon. These findings reveal that truncated zebrafish Gli2 proteins interfere with Hh signaling necessary for differentiation and axon guidance in the ventral forebrain. (+info)
Isolation and embryonic expression of the novel mouse gene Hic1, the homologue of HIC1, a candidate gene for the Miller-Dieker syndrome.
(5/2427)
The human gene HIC1 (hypermethylated in cancer) maps to chromosome 17p13.3 and is deleted in the contiguous gene disorder Miller-Dieker syndrome (MDS) [Makos-Wales et al. (1995) Nature Med., 1, 570-577; Chong et al. (1996) Genome Res., 6, 735-741]. We isolated the murine homologue Hic1, encoding a zinc-finger protein with a poxvirus and zinc-finger (POZ) domain and mapped it to mouse chromosome 11 in a region exhibiting conserved synteny to human chromosome 17. Comparison of genomic and cDNA sequences predicts two exons for the murine Hic1. The second exon exhibits 88% identity to the human HIC1 on DNA level. During embryonic development, Hic1 is expressed in mesenchymes of the sclerotomes, lateral body wall, limb and cranio-facial regions embedding the outgrowing peripheral nerves during their differentiation. During fetal development, Hic1 additionally is expressed in mesenchymes apposed to precartilaginous condensations, at many interfaces to budding epithelia of inner organs, and weakly in muscles. We observed activation of Hic1 expression in the embryonic anlagen of many tissues displaying anomalies in MDS patients. Besides lissencephaly, MDS patients exhibit facial dysmorphism and frequently additional birth defects, e.g. anomalies of the heart, kidney, gastrointestinal tract and the limbs (OMIM 247200). Thus, HIC1 activity may correlate with the defective development of the nose, jaws, extremities, gastrointestinal tract and kidney in MDS patients. (+info)
Interaction of Gli2 with CREB protein on DNA elements in the long terminal repeat of human T-cell leukemia virus type 1 is responsible for transcriptional activation by tax protein.
(6/2427)
The long terminal repeat (LTR) of human T-cell leukemia virus type 1 (HTLV-1) has two distinct DNA elements, one copy of TRE2S and three copies of a 21-bp sequence that respond to the viral trans-activator protein, Tax. Either multiple copies of the 21-bp sequence or a combination of one copy each of TRE2S and 21-bp sequence is required for efficient trans activation by Tax. In the trans activation of multiple copies of 21-bp sequence, CREB/ATF protein plays an essential role in forming a complex with Tax. To understand the role of TRE2S in trans activation of one copy of 21-bp sequence, we examined protein binding to the DNA elements by DNA affinity precipitation assay including Gli2 protein binding to TRE2S and CREB protein binding to 21-bp sequence. Binding of CREB to a DNA probe containing both elements, TRE2S-21bp probe, was dependent on Gli2 protein under restricted conditions and was enhanced in a dose-dependent fashion by the binding of Gli2 protein to the same probe. Mutation in either element abolished the efficient binding of CREB. A glutathione S-transferase fusion protein of a fragment of Gli2 was able to bind to CREB. Therefore, Gli2-CREB interaction on the DNA probe is proposed to stabilize CREB binding to DNA. Tax can bind to CREB protein on the DNA; therefore, stabilization of DNA binding of CREB results in more recruitment of Tax onto DNA. Conversely, Tax increased the DNA binding of CREB, although it had almost no effect on the binding of Gli2. These results suggest that Gli2 binds to the DNA element and interacts with CREB, resulting in more recruitment of Tax, which in turn stabilizes DNA binding of CREB. Similar cooperation of the protein binding to TRE2S-21bp probe was also observed in nuclear extract of an HTLV-1-infected T-cell line. Consistent with the Gli2-CREB interaction on the DNA elements, Tax-mediated trans activation was dependent on the size of the spacer between TRE2S and 21-bp sequence. The effective sizes of the spacer suggest that TRE2S in the LTR would cooperate with the second and third copies of the 21-bp sequence and contribute to trans activation of the viral gene transcription. (+info)
Sonic Hedgehog-induced activation of the Gli1 promoter is mediated by GLI3.
(7/2427)
Drosophila transcription factor cubitus interruptus (Ci) and its co-activator CRE (cAMP response element)-binding protein (CBP) activate a group of target genes on the anterior-posterior border in response to hedgehog protein (Hh) signaling. In the anterior region, in contrast, the carboxyl-truncated form of Ci generated by protein processing represses Hh expression. In vertebrates, three Ci-related transcription factors (glioblastoma gene products (GLIs) 1, 2, and 3) were identified, but their functional difference in Hh signal transduction is unknown. Here, we report distinct roles for GLI1 and GLI3 in Sonic hedgehog (Shh) signaling. GLI3 containing both repression and activation domains acts both as an activator and a repressor, as does Ci, whereas GLI1 contains only the activation domain. Consistent with this, GLI3, but not GLI1, is processed to generate the repressor form. Transcriptional co-activator CBP binds to GLI3, but not to GLI1. The trans-activating capacity of GLI3 is positively and negatively regulated by Shh and cAMP-dependent protein kinase, respectively, through a specific region of GLI3, which contains the CBP-binding domain and the phosphorylation sites of cAMP-dependent protein kinase. GLI3 directly binds to the Gli1 promoter and induces Gli1 transcription in response to Shh. Thus, GLI3 may act as a mediator of Shh signaling in the activation of the target gene Gli1. (+info)
GLI3 mutations in human disorders mimic Drosophila cubitus interruptus protein functions and localization.
(8/2427)
Truncation mutations of the GLI3 zinc finger transcription factor can cause Greig cephalopolysyndactyly syndrome (GCPS), Pallister-Hall syndrome (PHS), and postaxial polydactyly type A (PAP-A). GLI3 is homologous to Drosophila Cubitus interruptus (Ci), which regulates the patched (ptc), gooseberry (gsb), and decapentaplegic (dpp) genes. Ci is sequestered in the cytoplasm and is subject to posttranslational processing whereby the full-length transcriptional activator form (Ci155) can be cleaved to a repressor form (Ci75). Under hedgehog signaling, the Ci155 form translocates to the nucleus whereas in the absence of hedgehog, the Ci75 form translocates to the nucleus. Based on the correlation of GLI3 truncation mutations and the human phenotypes, we hypothesized that GLI3 shows transcriptional activation or repression activity and subcellular localization similar to Ci. Here we show that full-length GLI3 localizes to the cytoplasm and activates PTCH1 expression, which is similar to full-length Ci155. PHS mutant protein (GLI3-PHS) localizes to the nucleus and represses GLI3-activated PTCH1 expression, which is similar to Ci75. The GCPS mutant protein has no effect on GLI3-activated PTCH1 transcription, consistent with the role of haploinsufficiency in this disorder. The PAP-A mutant protein (GLI3-PAP-A) showed less specific subcellular localization but still inhibited GLI3-activated PTCH1 transcription, suggesting it may be a weaker allele than the GLI3-PHS mutation. These data show that GLI3 mutations in humans mimic functional effects of the Drosophila ci gene and correlate with the distinct effects of these mutations on human development. (+info)