Elf3 encodes a novel 200-kD β-spectrin: role in liver development

Abstract

b-spectrins are crucial for the maintenance of cell shape, the establishment of cell polarity, and the formation of distinct membrane domains. Our strategy for identifying genes important for hepatocyte polarity has been to utilize subtractive hybridization of early embryonic mouse cDNA liver libraries. As a result, we have cloned three isoforms of a novel b-spectrin elf (embryonic liver b-fodrin), and here we report the analysis of elf3, the longest isoform (8172 nt). ELF3 comprises 2154 residues with an overall similarity of 89.0% and 95.3% to mouse b-spectrin (bSpIIS1) at the nucleotide and amino acid level, respectively. ELF3 is characterized by an actinbinding domain, a long repeat domain, and a short regulatory domain remarkable for the absence of a PH domain. Linkage analysis reveals that elf3 maps to mouse chromosome 11 between D11Bir6 and D11Xrf477, a di erent chromosomal locus from that of the other four spectrin genes. Northern blot analysis utilizing an elf3 3'-UTR probe demonstrates an abundant 9.0-kb transcript in brain, liver, and heart tissues. Western blot with a polyclonal antibody against ELF identi®es a 200 kD protein in mouse liver, brain, kidney, and heart tissues. Immunohistochemical studies demonstrate ELF labeling of the basolateral or sinusoidal membranes surface as well as a granular cytoplasmic pattern in hepatocytes. Antisense studies utilizing cultured liver explants show a vital role of elf3 in hepatocyte di erentiation and intrahepatic bile duct formation. The di erential expression, tissue localization, and functional studies demonstrate the importance of elf3 in modulating interactions between various components of the cytoskeleton proteins controlling liver and bile duct development.

Critical interactions between TGF-β signaling/ELF, and E-cadherin/β-catenin mediated tumor suppression

“…This is also evidenced by our observation that disruption of ELF (a b-Spectrin), in turn, disrupts TGF-b signaling as a result of mislocalization of Smad3 and Smad4 (Tang Y et al, 2003). ELF was originally identified from endodermal stem/progenitor cells committed to foregut lineage (Mishra et al, 1998(Mishra et al, , 1999. Also, ELF, as a b-Spectrin and a major dynamic scaffolding protein, is important for the generation of functionally distinct membranes, protein sorting, cell adhesion and the development of a polarized differentiated epithelial cell (Tang et al, 2005).…”

“…To explore the role of ELF in the maintenance of adherens junctions and control of gastric epithelial cell polarity, proliferation and differentiation, we investigated the possibility of rescuing E-cadherin expression and normal cell-cell adhesion in the elf þ /À /Smad4 þ /À mutants through restoration of ELF activity. A fulllength elf cDNA clone was constructed that encodes the N-terminal actin and membrane binding domain, as well as the C-terminal domain that includes the ankyrin binding region, active phosphorylation sites at serine residues, and a hinge region that regulates oligomer formation (Mishra et al, 1998(Mishra et al, , 1999. Correction of cell-cell contacts by transient transfection of elf þ /À / Smad4 þ /À gastric cells with full-length elf was confirmed by rescue of substrate independent cell-cell adhesion (Figure 9c), but not with Smad3 or Smad4.…”

Disruption of transforming growth factor-β signaling through β-spectrin ELF leads to hepatocellular cancer through cyclin D1 activation

“…Smad function is highly dependent upon adaptor proteins such as embryonic liver fodrin (ELF), SARA and microtubules (Tsukazaki et al, 1998;Tang et al, 2003;Mishra et al, 2005). ELF, a b-spectrin, is first isolated from mouse E11 libraries and is shown to play a crucial role in the propagation of TGF-b signaling (Mishra et al, 1999). Specifically, ELF associates with Smad3 and the TGF-b receptor complex; this interaction is followed by interaction with Smad4 and leads to their translocation to the nucleus.…”

Transforming growth factor‐β in liver cancer stem cells and regeneration

“…When mature hepatocytes and cholangiocytes are damaged or inhibited in their replication, however, a reserve compartment of hepatic progenitor cells are activated 133. In human liver donor transplant recipients, early on within the first 6 weeks, expansion of cells expressing stem cell markers Oct3/4, AFP, and TGF‐β members is observed in zone 1, zone 2,28 and surprisingly also zone 3 (central vein)134, 135, 136 and appears to give rise to hepatocytes. These studies suggest that in submassive hepatic necrosis with intact zones 1 and 2, cells express stem cell markers and potentially lead the regenerative process 28, 33.…”