Subcellular localization of the oncoprotein MTG8 (CDR/ETO) in neural cells

Abstract

The t(8;21) translocation associated with acute myeloid leukemia (AML) disrupts two genes, the AML1 gene also known as the core binding factor A2 (CBFA2) on chromosome 21, and a gene on chromosome 8, hereafter referred to as MTG8, but also known as CDR and ETO. Extensive information is available on AML1, a member of the CBF family of transcription factors, containing a highly conserved domain, the runt box, of the Drosophila segmentation gene runt. This gene is essential for the hematopoietic development and is found disrupted in several leukemias. In contrast, the function of the MTG8 gene is poorly understood. The predicted protein sequence shows two unusual, putative zinc-®ngers, three proline-rich regions, a PEST domain and several phosphorylation sites. In addition, we found a region encompassing aa 443 ± 514 predicted to have a signi®cant propensity to form coiled coil structures. MTG8 displays a high degree of similarity with nervy, a homeotic target gene of Drosophila, expressed in the nervous system. Human and mouse wild-type MTG8 are also highly expressed in brain relative to other tissues. For these reasons, we set out to investigate the expression and subcellular localization of the MTG8 protein in neural cells. Immunohistochemical experiments in a 12.5-dayold mouse embryo clearly showed that the protein was expressed in the neural cells of the developing brain and the spinal cord. In primary cultures of hippocampal neurons of 2 ± 3 day-old mice, MTG8 was found in the nucleus, in the cytoplasm and as ®ne granules in the neurites. Cytoplasmic localization of the protein was observed in Purkinje cells of both human and mouse cerebellum. The molecular mass of MTG8 in total human and mouse brain was analysed by immunoblotting and determined to be between 70 and 90 kDa. Isoforms with the same molecular mass were demonstrated in synaptosomes isolated from mouse forebrain. The evidence of MTG8 in the nucleus and cytoplasm of neural cells suggests a speci®c mechanism regulating the subcellular localization of the protein.

Characterization of a t(5;8)(q31;q21) translocation in a patient with mental retardation and congenital heart disease: implications for involvement of RUNX1T1 in human brain and heart development

“…The strongest nuclear expression was observed in neurons in the cortical plate. These data support the previously reported nuclear localization of RUNX1T1 in mouse neurons 10 and suggest that RUNX1T1 is involved in differentiation of cortical Characterization of a t(5;8)(q31;q21) translocation L Zhang et al neurons in human. Interestingly, a similar expression pattern of RUNX1T1 was observed during hematopoietic differentiation of murine embryonic stem (ES) cells.…”

“…Thus, RUNX1T1 seems to play a role during stem cell differentiation, at least in hematopoietic and neuronal differentiation. The cytoplasmic staining in neurons of the nucleus ambiguous in a 16-week-old fetus supports previous observations in hippocampal neurons 10 and suggests that RUNX1T1 may have multiple roles during brain development. QPCR analysis of 25 hearts dissected from human embryos at different developmental stages suggests that RUNX1T1 expression level in the heart peaks around day 48 post fertilization.…”

“…The abundant expression in the developing brain is in agreement with previous investigations. 10,20 Involvement of RUNX1T1 in brain development was further investigated using immunohistochemical analysis of human embryonic and fetal tissue sections. In a 5-week-old embryo we observed strong and distinct staining in the perinuclear membrane of neural stem cells in the germinal matrix (ventricular zone) of the entire CNS.…”

The transcriptional corepressor MTG16a contains a novel nucleolar targeting sequence deranged in t (16; 21)-positive myeloid malignancies

“…These data fully support our previous protein findings (Sacchi et al, 1996(Sacchi et al, , 1998. In contrast, we could not detect either endogenous MTG16a or MTGR1a proteins in any hematopoietic cell line, which we screened so far (data not shown), even when we amplified the corresponding transcripts by RT -PCR (Figure 2g).…”

Breakpoint sequences of an 1;8 translocation in a family with Gilles de la Tourette syndrome

“…28 The nervy gene in Drosophila is similar to CBFA2T1 in sequence and is a target of the ultrabithorax homeotic gene product. 34,35 CBFA2T1 coding, 5' and 3' sequences are very highly conserved between humans and mice. 36 Although CBFA2T1 was not directly disrupted by the translocation breakpoint in the GTS family we studied, it is still possible that the translocation significantly altered the expression of CBFA2T1 (or another nearby gene).…”