Expression of Id1 Results in Apoptosis of Cardiac Myocytes through a Redox-dependent Mechanism

Abstract

We have constructed a recombinant adenovirus (Ad.Id1) that allows for efficient expression of the helixloop-helix protein Id1. After infection with Ad.Id1, neonatal cardiac myocytes display a significant reduction in viability, which was proportional to the level of Id1 expression. A similar effect was observed in adult myocytes. Morphological and biochemical assays demonstrated that Id1 expression resulted in myocyte apoptosis. In contrast, expression of Id1 in endothelial cells, vascular smooth muscle cells, or fibroblasts did not affect the viability of these cells. Along with the induction of apoptosis, the expression of Id1 in neonatal cardiac myocytes resulted in an increase in the level of intracellular reactive oxygen species. The source of these reactive oxygen species appears to be the mitochondria. Reducing the ambient oxygen concentration or treatment with a cell-permeant H 2 O 2 scavenger prevented Id1-stimulated apoptosis in cardiac myocytes. These results suggest that the expression of Id1 leads to the induction of apoptosis in cardiac myocytes through a redox-dependent mechanism.The Id family of proteins belongs to a class of nuclear proteins known as helix-loop-helix (HLH) 1 proteins, which regulate differentiation and tissue-specific gene expression. To date, four different Id family members have been identified (1-6). Although these four proteins share a high degree of homology, especially within the HLH domain, evidence suggests that they exert nonoverlapping functions (7-9).The HLH domain acts as a protein dimerization motif. Members of the HLH protein family which act to regulate transcription positively also contain an additional basic domain that mediates binding to DNA. In contrast, members of the Id family lack this domain and therefore are unable to bind DNA. These structural differences have led to a model in which Id proteins act in a dominant negative fashion to inhibit differentiation (1, 2). Under these circumstances, expression of high levels of Id1 would result in the binding and subsequent inactivation of basic domain HLH proteins.Consistent with this model of Id function is the observation that Id expression decreases when skeletal muscle cells differentiate (10). In addition, forced expression of Id has been shown to inhibit tissue-specific gene expression or differentiation of a variety of cell types (1, 10 -12). Previous reports have demonstrated that Id levels are high in embryonic hearts and decrease after birth (13-15). Such a shift in Id expression is consistent with its role as an inhibitor of differentiation. Although Id expression is low or absent in adult cardiac myocytes in culture, its expression can be reactivated by certain stimuli, such as ␣-adrenergic agonists (14, 15). A similar induction of Id expression has been demonstrated in skeletal muscle after treatment with the cardiotoxic chemotherapeutic agent doxorubicin (16,17).Although previous studies have demonstrated that forced expression of Id proteins can block differentiation, relatively little is known a...

Id-1gene downregulation by sulindac sulfide and its upregulation during tumor development in gastric cancer

“…Several studies have reported that Id-1 expression induced apoptosis in normal cells. 11,40 In contrast, in prostate cancer cells, Id-1 expression leads to protection against apoptosis. 41 At this time, we do not know why sulindac sulfide reduces Id-1 expression, nor do we have an explanation for the role of Id-1 on apoptosis; further studies are required to understand this.…”

Expression profiling reveals distinct sets of genes altered during induction and regression of cardiac hypertrophy

“…Eight of the fifteen were identified in previous studies of hypertrophy (Table 1) whereas three show no similarity to known genes. Included in this group are IGF-II, an orphan tyrosine kinase receptor MRK that is implicated in cardiac development, two kinases (JAK3 and MEK kinase), and a negative regulator of basis helix-loop-helix transcription factors (Id1) that has been implicated in cardiac myocyte apoptosis (42).…”

The helix–loop–helix protein ID1 localizes to centrosomes and rapidly induces abnormal centrosome numbers

“…This phosphorylation event may be a trigger for their ubiquitin-mediated proteasomal degradation and/or alter their bHLH protein binding specificities (Bounpheng et al, 1999;Deed et al, 1997). Various functions of the individual ID-proteins have been described to date: inhibition of differentiation by interfering with differentiation-specific bHLH factors (Benezra et al, 1990;Jen et al, 1992;Kreider et al, 1992), interference with non-bHLH transcription factors (Ohtani et al, 2001;Roberts et al, 2001), induction of apoptosis (Florio et al, 1998;Tanaka et al, 1998;Andres-Barquin et al, 1999), cooperation with the pRb pathway (Iavarone et al, 1994;Hara et al, 1996), and extension of life span (Alani et al, 1999;Nickoloff et al, 2000;Tang et al, 2002). These biological activities are consistent with the model that ID-proteins may directly contribute to tumorigenesis.…”