Bibhuti Mishra

Progenitor/stem cells give rise to liver cancer due to aberrant TGF-β and IL-6 signaling

Cancer stem cells (CSCs) are critical for the initiation, propagation, and treatment resistance of multiple cancers. Yet functional interactions between specific signaling pathways in solid organ “cancer stem cells,” such as those of the liver, remain elusive. We report that in regenerating human liver, two to four cells per 30,000–50,000 cells express stem cell proteins Stat3, Oct4, and Nanog, along with the prodifferentiation proteins TGF-β-receptor type II (TBRII) and embryonic liver fodrin (ELF). Examination of human hepatocellular cancer (HCC) reveals cells that label with stem cell markers that have unexpectedly lost TBRII and ELF. elf+/− mice spontaneously develop HCC; expression analysis of these tumors highlighted the marked activation of the genes involved in the IL-6 signaling pathway, including IL-6 and Stat3, suggesting that HCC could arise from an IL-6-driven transformed stem cell with inactivated TGF-β signaling. Similarly, suppression of IL-6 signaling, through the generation of mouse knockouts involving a positive regulator of IL-6, Inter-alpha-trypsin inhibitor-heavy chain-4 (ITIH4), resulted in reduction in HCC in elf+/− mice. This study reveals an unexpected functional link between IL-6, a major stem cell signaling pathway, and the TGF-β signaling pathway in the modulation of mammalian HCC, a lethal cancer of the foregut. These experiments suggest an important therapeutic role for targeting IL-6 in HCCs lacking a functional TGF-β pathway.

Tgf-Beta signaling in development.

The transforming growth factor–β (TGF-β) superfamily comprises nearly 30 growth and differentiation factors that include TGF-βs, activins, inhibins, and bone morphogenetic proteins (BMPs). Multiple members of the TGF-β superfamily serve key roles in stem cell fate commitment. The various members of the family can exhibit disparate roles in regulating the biology of embryonic stem (ES) cells and tumor suppression. For example, TGF-β inhibits proliferation of multipotent hematopoietic progenitors, promotes lineage commitment of neural precursors, and suppresses epithelial tumors. BMPs block neural differentiation of mouse and human ES cells, contribute to self-renewal of mouse ES cells, and also suppress tumorigenesis. ES cells and tumors may be exposed to multiple TGF-β members, and it is likely that the combination of growth factors and cross-talk among the intracellular signaling pathways is what precisely defines stem cell fate commitment. This Connections Map Pathway in the Database of Cell Signaling integrates signaling not only from TGF-β and BMP but also from the ligands nodal and activin, and describes the role of the signaling pathways activated by these ligands in mammalian development. Much of the evidence for the connections shown comes from studies on mouse and human ES cells or mouse knockouts. This pathway is important for understanding not only stem cell biology, but also the molecular effectors of TGF-β and BMP signaling that may contribute to cancer suppression or progression and thus are potential targets for therapeutic intervention.

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

Transforming growth factor-β (TGF-β) signaling members, TGF-β receptor type II (TBRII), Smad2, Smad4 and Smad adaptor, embryonic liver fodrin (ELF), are prominent tumor suppressors in gastrointestinal cancers. Here, we show that 40% of elf+/− mice spontaneously develop hepatocellular cancer (HCC) with markedly increased cyclin D1, cyclin-dependent kinase 4 (Cdk4), c-Myc and MDM2 expression. Reduced ELF but not TBRII, or Smad4 was observed in 8 of 9 human HCCs (P<0.017). ELF and TBRII are also markedly decreased in human HCC cell lines SNU-398 and SNU-475. Restoration of ELF and TBRII in SNU-398 cells markedly decreases cyclin D1 as well as hyperphosphorylated-retinoblastoma (hyperphosphorylated-pRb). Thus, we show that TGF-β signaling and Smad adaptor ELF suppress human hepatocarcinogenesis, potentially through cyclin D1 deregulation. Loss of ELF could serve as a primary event in progression toward a fully transformed phenotype and could hold promise for new therapeutic approaches in human HCCs.

Hepatocellular Cancer Arises from Loss of Transforming Growth Factor Beta Signaling Adaptor Protein Embryonic Liver Fodrin Through Abnormal Angiogenesis

We have previously demonstrated that 40%‐70% of elf+/− mice spontaneously develop hepatocellular cancer (HCC) within 15 months, revealing the importance of the transforming growth factor‐beta (TGF‐β) signaling pathway in suppressing tumorigenesis in the liver. The current study was carried out to investigate mechanisms by which embryonic liver fodrin (ELF), a crucial Smad3/4 adaptor, suppresses liver tumor formation. Histological analysis of hyperplastic liver tissues from elf+/− mice revealed abundant newly formed vascular structures, suggesting aberrant angiogenesis with loss of ELF function. In addition, elf+/− mice displayed an expansion of endothelial progenitor cells. Ectopic ELF expression in fetal bovine heart endothelial (FBHE) cells resulted in cell cycle arrest and apoptosis. Further analysis of developing yolk sacs of elf−/− mice revealed a failure of normal vasculature and significantly decreased endothelial cell differentiation with embryonic lethality. Immunohistochemical analysis of hepatocellular cancer (HCC) from the elf+/− mice revealed an abnormal angiogenic profile, suggesting the role of ELF as an angiogenic regulator in suppressing HCC. Lastly, acute small interfering RNA (siRNA) inhibition of ELF raised retinoblastoma protein (pRb) levels nearly fourfold in HepG2 cells (a hepatocellular carcinoma cell line) as well as in cow pulmonary artery endothelial (CPAE) cells, respectively. Conclusion: Taken together these results, ELF, a TGF‐β adaptor and signaling molecule, functions as a critical adaptor protein in TGF‐β modulation of angiogenesis as well as cell cycle progression. Loss of ELF in the liver leads the cancer formation by deregulated hepatocyte proliferation and stimulation of angiogenesis in early cancers. Our studies propose that ELF is potentially a powerful target for mimetics enhancing the TGF‐β pathway tumor suppression of HCC. (HEPATOLOGY 2008.)

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

Inactivation of the transforming growth factor-β (TGF-β) pathway occurs often in malignancies of the gastrointestinal (GI) system. However, only a fraction of sporadic GI tumors exhibit inactivating mutations in early stages of cancer formation, suggesting that other mechanisms play a critical role in the inactivation of this pathway. Here, we show a wide range of GI tumors, including those of the stomach, liver and colon in elf+/− and elf+/−/Smad4+/− mutant mice. We found that embryonic liver fodrin (ELF), a β-Spectrin originally identified in endodermal stem/progenitor cells committed to foregut lineage, possesses potent antioncogenic activity and is frequently inactivated in GI cancers. Specifically, E-cadherin accumulation at cell–cell contacts and E-cadherin-β-catenin-dependent epithelial cell–cell adhesion is disrupted in elf+/−/Smad4+/− mutant gastric epithelial cells, and could be rescued by ectopic expression of full-length elf, but not Smad3 or Smad4. Subcellular fractionation revealed that E-cadherin is expressed mainly at the cell membrane after TGF-β stimulation. In contrast, elf+/−/Smad4+/− mutant tissues showed abnormal distribution of E-cadherin that could be rescued by overexpression of ELF but not Smad3 or Smad4. Our results identify a group of common lethal malignancies in which inactivation of TGF-β signaling, which is essential for tumor suppression, is disrupted by inactivation of the ELF adaptor protein.

Inactivation of ELF/TGF- β signaling in human gastrointestinal cancer

TGF-β/Smads regulate a wide variety of biological responses through transcriptional regulation of target genes. ELF, a β-spectrin, plays a key role in the transmission of TGF-β-mediated transcriptional response through Smads. ELF was originally identified as a key protein involved in endodermal stem/progenitor cells committed to foregut lineage. Also, as a major dynamic adaptor and scaffolding protein, ELF is important for the generation of functionally distinct membranes, protein sorting and the development of polarized differentiated epithelial cells. Disruption of elf results in the loss of Smad3/Smad4 activation and, therefore, a disruption of the TGF-β pathway. These observations led us to pursue the function of ELF in gastrointestinal (GI) epithelial cell–cell adhesion and tumor suppression. Here, we show a significant loss of ELF and reduced Smad4 expression in human gastric cancer tissue samples. Also, of the six human gastric cancer cell lines examined, three show deficient ELF expression. Furthermore, we demonstrate the rescue of E-cadherin-dependent homophilic cell–cell adhesion by ectopic expression of full-length elf. Our results suggest that ELF has an essential role in tumor suppression in GI cancers.

RING finger-dependent ubiquitination by PRAJA is dependent on TGF- β and potentially defines the functional status of the tumor suppressor ELF

In gastrointestinal cells, biological signals for transforming growth factor-beta (TGF-β) are transduced through transmembrane serine/threonine kinase receptors that signal to Smad proteins. Smad4, a tumor suppressor, is often mutated in human gastrointestinal cancers. The mechanism of Smad4 inactivation, however, remains uncertain and could be through E3-mediated ubiquitination of Smad4/adaptor protein complexes. Disruption of ELF (embryonic liver fodrin), a Smad4 adaptor protein, modulates TGF-β signaling. We have found that PRAJA, a RING-H2 protein, interacts with ELF in a TGF-β-dependent manner, with a fivefold increase of PRAJA expression and a subsequent decrease in ELF and Smad4 expression, in gastrointestinal cancer cell lines (P<0.05). Strikingly, PRAJA manifests substantial E3-dependent ubiquitination of ELF and Smad3, but not Smad4. Δ-PRAJA, which has a deleted RING finger domain at the C terminus, abolishes ubiquitination of ELF. A stable cell line that overexpresses PRAJA exhibits low levels of ELF in comparison to a Δ-PRAJA stable cell line, where ELF expression is high compared to normal controls. The alteration of ELF and/or Smad4 expression and/or function in the TGF-β signaling pathway may be induced by enhancement of ELF degradation, which is mediated by a high-level expression of PRAJA in gastrointestinal cancers. In hepatocytes, half-life (t1/2) and rate constant for degradation (kD) of ELF is 1.91 h and 21.72 min−1 when coupled with ectopic expression of PRAJA in cells stimulated by TGF-β, compared to PRAJA-transfected unstimulated cells (t1/2=4.33 h and kD=9.6 min−1). These studies reveal a mechanism for tumorigenesis whereby defects in adaptor proteins for Smads, such as ELF, can undergo degradation by PRAJA, through the ubiquitin-mediated pathway.

Loss of cooperative function of transforming growth factor-β signaling proteins, smad3 with embryonic liver fodrin, a β -spectrin, in primary biliary cirrhosis

Abstract: Modulation of fibrogenesis, epithelial, and mesenchymal cell fates are prominent effects of transforming growth factor‐β (TGF‐β) signaling by Smad proteins. We have previously shown that Smad2 and Smad3 insufficiency leads to a loss of bile ducts. In addition, Smad3/4 activity is mediated by embryonic liver fodrin (ELF), a β‐Spectrin. In mouse elf−/− mutants and in liver explant cultures, loss of ELF function results in T lymphocytic proliferation and absent intrahepatic bile ducts. A similar phenotype is seen in a number of cholestatic diseases with progressive loss of intrahepatic bile ducts and fibrosis. However, the expression patterns of Smads or role of ELF in cholestatic and fibrotic liver diseases are not yet known.

ELF a β-spectrin is a neuronal precursor cell marker in developing mammalian brain; structure and organization of the elf/β-G spectrin gene

Spectrins play a pivotal role in axonal transport, neurite extension, the organization of synaptic vesicles, as well as for protein sorting in the Golgi apparatus and cell membrane. Among spectrins there is great variability in sequence composition, tissue distribution, and function, with two known genes encoding the α-chain, and at least five encoding the β-chain. It remains unclear as to whether novel β-spectrins such as elf1-4are distinct genes or β-G-spectrin isoforms. The role for ELF in the developing nervous system has not been identified to date. In this study we demonstrate the genomic structure of elf-3, as well as the expression of ELF in the developing mouse brain using a peptide specific antibody against its distinctive amino-terminal end. Full genomic structural analyses reveal that elf-3is composed of 31 exons spanning ∼67˜kb, and confirm that elfand mouse brain β-G-spectrin share multiple exons, with a complex form of exon/intron usage. In embryonic stages, E9–12, anti-ELF localized to the primary brain vesicular cells that also labeled strongly with anti-nestin but not anti-vimentin. At E12–14, anti-ELF localized to axonal sprouts in the developing neuroblasts of cortex and purkinje cell layer of the cerebellum, as well as in cell bodies in the diencephalon and metencephalon. Double labeling identified significant co-localization of anti-ELF, nestin and dystrophin in sub ventricular zone cells and in stellate-like cells of the developing forebrain. These studies define clearly the expression of ELF, a new isoform of β-G-spectrin in the developing brain. Based on its expression pattern, ELF may have a role in neural stem cell development and is a marker of axonal sprouting in mid stages of embryonic development.

TGF-β signaling in neuronal stem cells

Transforming growth factor beta (TGF-β) signaling has diverse and complex roles in various biological phenomena such as cell growth, differentiation, embryogenesis and morphogenesis. ES cells provide an essential model for understanding the role of TGF-β signaling in lineage specification and differentiation. Recent studies have suggested significant role of TGF-β in stem/progenitor cell biology. Here in this review, we focus on the role of the TGF-β superfamily in neuronal development.