Sp1-like zinc finger transcription factors are involved in the regulation of cell growth and differentiation. Recent evidence demonstrating that mammalian cells express novel, yet uncharacterized, Sp1-like proteins has stimulated a search for new members of this family. We and others have recently reported that the transforming growth factor (TGF)--regulated gene TIEG encodes a new Sp1-like protein that inhibits cell growth in cultured cells. Here we report the identification, nuclear localization, DNA binding activity, transcriptional repression activity, and growth inhibitory effects of TIEG2, a novel TGF--inducible gene related to TIEG. TIEG2 is ubiquitously expressed in human tissues, with an enrichment in pancreas and muscle. TIEG2 shares 91% homology with TIEG1 within the zinc finger region and 44% homology within the N terminus. Biochemical characterization reveals that TIEG2 is a nuclear protein, which, as predicted from the primary structure, specifically binds to an Sp1-like DNA sequence in vitro and can repress a promoter containing Sp1-like binding sites in transfected Chinese hamster ovary epithelial cells. Furthermore, functional studies using [ The transcription factor Sp1 is the founding member of a family of zinc finger proteins that regulate a variety of genes involved in cell growth and differentiation (1-22). Sp1-like binding sites, for example, are critical for the expression of a large group of genes necessary for DNA synthesis and cell cycle progression (2, 14 -22). In addition, the overexpression of some members of the Sp1-like family of proteins in cultured cells has been shown to induce cell proliferation, cell cycle arrest, or apoptosis (9, 10, 13, 23). Furthermore, the disruption of Sp1 by homologous recombination demonstrates that at least some members of this subfamily of proteins are essential for normal development in vivo (24). Thus, Sp1-like proteins are emerging as critical regulators of the cellular events underlying morphogenesis.The current members within the Sp1-like family of proteins include Sp1, Sp2, Sp3, Sp4, BTEB1, BTEB2, CPBP, BKLF, EKLF, GKLF, LKLF, and TIEG 1 (1, 3-15). These proteins are characterized by the presence of three highly conserved Cterminal zinc finger domains, which bind to GC-rich sequences. The growth regulatory effects of these proteins are believed to be mediated by the tight regulation of a hierarchical cascade of gene expression resulting from their binding to cis-regulatory GC-rich sites and subsequent interaction with the basal transcriptional machinery (25)(26)(27)(28)(29). In several instances, the identity of the specific Sp1-like protein that regulates distinct promoters through GC-rich sequences has been determined (5, 7, 14 -22). However, emerging evidence reveals that GC-rich sequences in other promoters bind to as yet uncharacterized proteins (22, 30 -36). This evidence has led many laboratories to search for novel members of the Sp1-like proteins. We and others, for example, have recently reported that the TIEG gene encodes an Sp1-li...
Sp1-like transcription factors are characterized by three highly homologous C-terminal zinc finger motifs that bind GC-rich sequences. These proteins behave as either activators or repressors and have begun to be classified into different subfamilies based upon the presence of conserved motifs outside the zinc finger domain. This classification predicts that different Sp1-like subfamilies share certain functional properties. TIEG1 and TIEG2 constitute a new subfamily of transforming growth factor--inducible Sp1-like proteins whose zinc finger motifs also bind GC-rich sequences. However, regions outside of the DNA-binding domain that differ in structure from other Sp1-like family members remain poorly characterized. Here, we have used extensive mutagenesis and GAL4-based transcriptional assays to identify three repression domains within TIEG1 and TIEG2 that we call R1, R2, and R3. R1 is 10 amino acids, R2 is 12 amino acids, and R3 is approximately 80 amino acids long. None of these domains share homology with previously described transcriptional regulatory motifs, but they share strong sequence homology and are functionally conserved between TIEG1 and TIEG2. Together, these data demonstrate that TIEG proteins are capable of repressing transcription, define domains critical for this function, and further support the idea that different subfamilies of Sp1-like proteins have evolved to mediate distinct transcriptional functions.Sp1-like transcription factors have recently elicited significant attention because of their widespread participation in the regulation of mammalian cell homeostasis (1). Members of this family of proteins currently include Sp1-4, BTEB1, BTEB2/ IKLF, TIEG1/MGIF, TIEG2, BKLF, EKLF, GKLF/EZF, LKLF, CPBP/Bcd, and AP2-rep, all of which are characterized by three highly conserved C 2 H 2 zinc finger DNA-binding domains at their C termini (2-21). Sp1-like transcription factors share over 75% similarity within these three zinc finger domains. Because of this high similarity, it is not surprising that many of these proteins bind to similar GC-rich sequences within promoters (reviewed in Ref. 1). These GC-rich sequences contribute to the regulation of a large number of genes necessary for various cellular functions, including cell proliferation, differentiation, and apoptosis (22). Thus, because of their participation in these functions, many Sp1-like proteins also function as key regulators of morphogenesis (1).While the DNA-binding domain of the Sp1-like transcription factor family is highly conserved, the N-terminal regions of the proteins are more divergent. Interestingly, it is through this domain that many of these transcription factors regulate transcription (7,14,(17)(18)(19)(23)(24)(25)(26)(27)(28)(29)(30). The founding member of this family, Sp1, for example, is a potent transcriptional activator that utilizes glutamine-rich sequences located within its N terminus to interact with proteins from the basal transcriptional apparatus to regulate gene expression (23). In contrast, BKLF behaves a...
Dynamin proteins are members of a recently described family of GTPases involved in receptor-mediated processes. To date, three different dynamin-encoding genes have been identified in mammalian tissues. Dynamin I is expressed only in neurons, whereas dynamin II is ubiquitously expressed. A third isoform, dynamin Ill, was originally isolated from a rat testis cONA library and shown to be testis-specific. However, here we report the cloning and characterization of dynamin Ill from brain and lung, demonstrating a more extended pattern of expression for this isoform. In addition, we have investigated the temporal pattern of expression of these three genes during brain development. We find that both dynamin I and dynamin Ill mRNA levels are up-regulated during embryogenesis, whereas dynamin II mRNA levels remain unchanged. From these results, we conclude that dynamin Ill is not a testis-specific isoform and, furthermore, that rat brain expresses three different dynamin-encoding genes that are differentially regulated during development. Therefore, this large isoform diversity of dynamin proteins in brain predicts a significant complexity in the understanding of dynamin-based processes in this tissue. Key Words: Dynamin-encoding genes-Brain-Development-Differential expression-PC12 cells.
Members of the dynamin superfamily are GTPases which have been shown to support receptor-mediated endocytosis in vivo and bind to growth factor receptor-associated proteins in vitro. In acinar cells of the pancreas, receptor-mediated endocytosis is very important for the recycling of membranes after secretory granule release. Therefore, characterization of the molecular machinery responsible for this process is critical for a better understanding of this phenomenon. In this study we sought to determine the expression pattern of the endocytic GTPase dynamin II during pancreatic acinar cell differentiation in developing rat embryos and in dexamethasone-treated AR42J cells using Western blot, Northern blot, and immunocytochemical analyses. During pancreatic development, dynamin immunoreactivity is almost undetectable until day E17 but undergoes significant upregulation in acinar cells starting at E18. In addition, the levels of dynamin mRNA and protein in AR42J cells increase approximately threefold during dexamethasone-induced acinar differentiation. The increase in dynamin levels that occurs in both embryonic pancreatic cells and dexamethasone-treated AR42J cells correlates with the establishment of a more differentiated acinar phenotype. Therefore, these results suggest a potential role for dynamin in supporting receptor-mediated endocytosis in mature pancreatic acinar cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.