Daxx is essential for embryonic development and implicated in apoptosis and transcriptional regulation. It is found only in the animal kingdom and appears to arise first in insects. In the Drosophila genus, the Daxx orthologs are much larger than those in other species. Here we show that in addition to a conserved core of ~200 residues, Daxx possesses several conserved domains and two essentially invariable short SUMO-interacting motifs (SIMs), each located at one or the other terminus of the protein.
p53 SUMOylation promotes its nuclear export. The SIM-binding groove of a SUMO moiety linked to p53 and a SIM in CRM1 regulates their interaction. CRM1 binds to tetrameric p53 with a properly folded core domain, and CRM1 with a mutated SIM in the HEAT9 loop accumulates with SUMOylated p53 at NPCs and cytoplasmic aggregates.
In a genome-wide screen for putative tumor suppressor genes, the EBF3 locus on the human chromosome 10q26.3 was found to be deleted or methylated in 73% of the examined cases of brain tumors. EBF3 is expressed in normal brain but is silenced in brain tumors. Therefore, it is suggested that EBF3 is a tumor suppressor. However, it remains unknown whether inactivation of EBF3 locus also occurs in other types of tumors and what functions of EBF3 underlie EBF3-mediated tumor suppression. We show here that expression of EBF3 resulted in cell cycle arrest and apoptosis. The expression of cyclindependent kinase inhibitors was profoundly affected with early activation and then repression of p21 cip1/waf1 and persistent activation of both p27 kip1 and p57 kip2 , whereas genes involved in cell survival and proliferation were suppressed. EBF3 bound directly to p21 cip1/waf1 promoter and regulated transcription from both p21 cip1/waf1 and p27 kip1 promoters in reporter assays. Apoptosis occurred 48 hours after EBF3 expression with caspase-3 activation. Silencing of the EBF3 locus was observed in brain, colorectal, breast, liver, and bone tumor cell lines and its reactivation was achieved on treatment with 5-aza-2 ¶-deoxycytidine and trichostatin A in a significant portion of these tumor cells. Therefore, EBF3 regulates a transcriptional program underlying a putative tumor suppression pathway.
In an attempt to develop high producing mammalian cell lines expressing glucagon-like-peptide-1-antibody fusion proteins (GLP-1), we have noted that the N-terminal GLP-1 portion of the fusion protein was susceptible to proteolytic degradation during cell culture, which resulted in an inactive product. The majority of the N-terminal clipped product appeared to be due to the removal of the entire biologically active peptide (30 amino acids) from the intact molecule. A number of parameters that influenced the degradative process were investigated. Additionally, protease inhibitors specific for each class of protease were tested. Results suggested that one or more serine-threonine class of protease(s) were involved in this process and inhibitors that are specific for this class of protease, including benzamidine hydrochloride could significantly inhibit the proteolytic degradation of the fusion proteins. Identification of the specific proteases involved in this process by shotgun proteomics methodology will pave the way for engineering the CHOK1SV cell line which will serve as a superior host for the production of future fusion protein products.
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