The protein ENH is a cytoplasmic sequestration factor for Id2 in normal and tumor cells from the nervous system

Abstract

Id2 is a natural inhibitor of the basic helix-loop-helix transcription factors and the retinoblastoma tumor suppressor protein. Active Id2 prevents differentiation and promotes cell-cycle progression and tumorigenesis in the nervous system. A key event that regulates Id2 activity during differentiation is translocation from the nucleus to the cytoplasm. Here we show that the actin-associated protein enigma homolog (ENH) is a cytoplasmic retention factor for Id2. ENH contains three LIM domains, which bind to the helixloop-helix domain of Id proteins in vitro and in vivo. ENH is up-regulated during neural differentiation, and its ectopic expression in neuroblastoma cells leads to translocation of Id2 from the nucleus to the cytoplasm, with consequent inactivation of transcriptional and cell-cycle-promoting functions of Id2. Conversely, silencing of ENH by RNA interference prevents cytoplasmic relocation of Id2 in neuroblastoma cells differentiated with retinoic acid. Finally, the differentiated neural crest-derived tumor ganglioneuroblastoma coexpresses Id2 and ENH in the cytoplasm of ganglionic cells. These data indicate that ENH contributes to differentiation of the nervous system through cytoplasmic sequestration of Id2. They also suggest that ENH is a restraining factor of the oncogenic activity of Id proteins in neural tumors.differentiation ͉ enigma homolog ͉ Id proteins ͉ neural cancer I d2 is one of the four members of the Id protein family, a group of proteins known as inhibitor of differentiation (1, 2). Id2 lies at the center of a molecular network including the retinoblastoma (Rb) tumor suppressor protein and the basic helix-loop-helix (bHLH) transcription factors, the best-known targets for inhibition by Id2 (3, 4). These connections probably operate in a variety of cell types, but our work has characterized them in the nervous system (5-7). In this tissue, overexpression of Id proteins inhibits differentiation whereas ablation of Id genes induces premature differentiation of various neural cell types in vitro and in vivo (8-10). As physiologic regulator of Id2, Rb cooperates with bHLH transcription factors to promote cell-cycle arrest and differentiation in the developing brain. This pathway is subverted in tumor cells. Malignant transformation in the central and peripheral nervous system coincides with frequent elevation of Id2, a process typically implemented by the activation of oncoproteins such as Myc and Ews-Fli1 that up-regulate Id2 gene transcription, (6,7,11,12). The aberrant accumulation of Id2 contributes to uncontrolled proliferation and neoangiogenesis, two hallmarks of neural cancer (13).There is general agreement with the notion that differentiation of a variety of cell types requires elimination of Id function. However, the mechanisms by which the signaling pathways initiating differentiation in the nervous system inactivate Id proteins are unknown. Although Id are viewed mainly as nuclear proteins, recent papers reported that relocation of Id proteins to the cytoplasm is an effective...

FHL2 interacts with and acts as a functional repressor of Id2 in human neuroblastoma cells

“…However, treatment with RA (1 mM) induced a progressive and remarkable elevation of both FHL2 mRNA and protein levels. In accordance with previous reports (16,37), RA administration led to a marked inhibition of Id2 gene expression. In RA-untreated SH-SY5Y cells, the endogenous interaction of FHL2 and Id2 could not be detected by CoIP assays but could be detected in SH-SY5Y cells with 6 h RA treatment ( Figure 5B).…”

“…Rb binds to and antagonizes Id2 from binding to transcription factors, thus releasing bHLH protein-mediated transcription (10,14,15). Recently, cytoplasmic proteins such as enigma homolog (ENH), polycystin-2 (PC2) and interferon-induced protein p204 were reported to bind to Id2 and sequestrate it into cytoplasm, thus preventing the access of Id2 to its nuclear partners (16)(17)(18). Loss of the cytoplasmic adaptor ENH was suggested to boost Id2 activity in aggressive neuroblastomas (16).…”

“…Recently, cytoplasmic proteins such as enigma homolog (ENH), polycystin-2 (PC2) and interferon-induced protein p204 were reported to bind to Id2 and sequestrate it into cytoplasm, thus preventing the access of Id2 to its nuclear partners (16)(17)(18). Loss of the cytoplasmic adaptor ENH was suggested to boost Id2 activity in aggressive neuroblastomas (16). In view of the oncogenic activity of Id2, proteins that prevent Id2 from binding to bHLH factors may be potential tumor suppressors.…”

Over-expression of Id2 and Id3 Proteins Regulates Growth and Survival of Human Colon Carcinoma (HCT116) Cells

“…Evidence available suggests that Id proteins are localized in the cytoplasm rather than the nucleus in a variety of cells such as hemopoietic [20], neural [21], muscle [22], and renal cells [23]. These findings therefore suggest that translocation between the nucleus and the cytoplasm (nucleocytoplasmic shuttling) may be involved in the functional regulation of Id proteins.…”

Molecular mechanisms of reversing neural degeneration by retinoic acid, a major derivative of vitamin A

“…It is vital to understand the cell biology of neuro degenerative diseases and tissue malignance in order to design appropriate therapeutics. Intrinsic properties causing diseases such as uncontrolled transcription (Ruzinova and Benezra, 2003;Lasorella and Iavarone, 2006), Reactive Oxidative Species (ROS) accumulation (Eichele, 1997) and synthesis of molecules leading to apoptosis (Amtul et al, 2012) have been studied. In addition, extrinsic properties such as physical constrains, stress factors (Vogel, 2000) and toxic substances (Eichele, 1997) have also been examined and many approaches to address numerous pathological constraints have been under taken.…”