Disease relevance of Nrg1

• The amelioration of dystrophic phenotype by heregulin-mediated utrophin up-regulation offers a pharmacological therapeutic modality and obviates many of the toxicity and delivery issues associated with viral vector-based gene therapy for DMD [1].
• We thereby sought to determine whether overexpression of the extracellular region of HRG would be sufficient to induce mammary gland carcinomas [2].
• A HRG construct lacking the cytoplasmic domain was targeted to the mammary gland using the murine mammary tumor virus promoter [2].
• Based on these results, we propose that heregulin increases the expression of pro-invasive, pro-metastatic and anti-apoptotic genes in cancer cells through autocrine activation of NF-kappaB, which leads to invasive and drug-resistant growth of breast cancer [3].
• Interactions between progestins and heregulin (HRG) signaling pathways: HRG acts as mediator of progestins proliferative effects in mouse mammary adenocarcinomas [4].

High impact information on Nrg1

• We show that hyaluronan-deficient AVC explants from Has2(-/-) embryos, which normally lack mesenchyme formation, are rescued by heregulin treatment, which restores phosphorylation of ErbB2 and ErbB3 [5].
• The factors needed for these structures to develop include the transcription factor Mash1, the glial-derived neurotrophic factor GNDF and its receptor subunits, and the neuregulin signalling system, each of which is essential for the differentiation and survival of subsets of autonomic neurons [6].
• We show that C2 muscle cells contain erbB2 and erbB3 messenger RNA but little or no erbB4 mRNA, and that neuregulin stimulates tyrosine phosphorylation of erbB2 and erbB3, indicating that neuregulin signalling in skeletal muscle may be mediated by a complex of erbB2 and erbB3 [7].
• Neuregulins, identified originally as a potential ligand for erbB2 (Neu differentiation factor, NDF), stimulate proliferation of Schwann cells (glial growth factor, GGF), increase the rate of AChR synthesis in cultured muscle cells (AChR-inducing activity) and are expressed in motor neurons [7].
• Here we show that neuregulin activates AChR gene expression in C2 muscle cells and that the neuregulin response element in the AChR delta-subunit gene is contained in the same 181 base pairs that confer synapse-specific expression in transgenic mice [7].

Chemical compound and disease context of Nrg1

• Eight chimeric toxins composed of the extracellular and EGF-like domains of four different HRG isoforms and truncated Pseudomonas exotoxin (PE38KDEL) were constructed [8].
• Moreover, activation of the HER-2 receptor in breast cancer cells by the peptide growth factor, heregulin, leads to direct and rapid phosphorylation of ER on tyrosine residues [9].
• We demonstrated that HRG stimulation of human breast cancer cells and normal breast epithelial cells induces the expression of Rab3A protein and mRNA in a cycloheximide-independent manner [10].
• We found that Ebp1 was basally phosphorylated in AU565 breast cancer cells on serine/threonine residues and that this phosphorylation was enhanced by heregulin treatment [11].
• We demonstrated that in ovariectomized nude mice, HRG induced E2 independence and antiestrogen resistance and promoted metastasis and preneoplastic transformation of the adjacent mouse mammary tissue [12].

Biological context of Nrg1

• Reduced Nrg1 expression causes hypomyelination and reduced nerve conduction velocity [13].
• Here, we report a novel phenotype in mice with targeted mutations in the erbB2, erbB3, or neuregulin-1 genes [14].
• Heregulin (HRG)-induced tyrosine phosphorylation of the Gab2 docking protein was enhanced by pretreatment with wortmannin, indicating negative regulation via a PI3-kinase-dependent pathway [15].
• Sequential requirement of hepatocyte growth factor and neuregulin in the morphogenesis and differentiation of the mammary gland [16].
• Thus, HRG treatment of primary cultures of epithelial cells of the progestin-dependent C4HD murine mammary tumor line and of T47D cells induced a decrease of protein levels of PRA and -B isoforms and the downregulation of progesterone-binding sites [17].

Anatomical context of Nrg1

• Ig-Nrg1 isoforms are preferentially expressed by proprioceptive sensory neurons and are sufficient to induce muscle spindle differentiation in vivo, whereas CRD-Nrg1 isoforms are broadly expressed in sensory and motor neurons but are not required for muscle spindle induction [18].
• We provide genetic evidence that Neuregulin1 (Nrg1) is required for proprioceptive afferent-evoked induction of muscle spindle differentiation in the mouse [18].
• We suggest a model by which myelin-forming Schwann cells integrate axonal Nrg1 signals as a biochemical measure of axon size [13].
• Neuregulin-1 is expressed at the origin of neural crest cells [14].
• We provide evidence that migration of neural crest cells to the mesenchyme lateral of the dorsal aorta, in which they differentiate into sympathetic neurons, depends on neuregulin-1 and its receptors [14].

Associations of Nrg1 with chemical compounds

• Novel role for cyclin-dependent kinase 2 in neuregulin-induced acetylcholine receptor epsilon subunit expression in differentiated myotubes [19].
• HRG induced a potent proliferative effect on these cells and potentiated MPA mitogenic effects [4].
• Mammary tumor progression to a progestin-independent (HI) phenotype was accompanied by a high constitutive expression of HRG [4].
• In contrast, emodin, which blocks phosphorylation of her2/neu by heregulin, failed to reduce NF-kappaB activation [3].
• The major isoform synthesized by striatal NPs is a transmembrane type III isoform called cysteine-rich domain Nrg-1 [20].

Physical interactions of Nrg1

• Furthermore, the neural tube activity is blocked by a hybrid protein containing the NDF-binding domain of the ErbB4 receptor, strongly implicating NDF in the physiological transition [21].
• Heregulin receptors are unable to mediate the rapid internalization of bound ligand as demonstrated in cells transfected with chimeric or wild-type ErbB-2, -3, or -4 receptors (Baulida et al., 1996, J. Biol. Chem. 271, 5251-5257; Pinkas-Kramanski et al., 1996, EMBO J. 15, 2452-2467) [22].

Enzymatic interactions of Nrg1

• More Retinoblastoma protein was found in the hypophosphorylated state in the cells treated with mAb ID5, whereas more retinoblastoma protein was in the hyperphosphorylated state in heregulin-treated cells [23].
• Furthermore, neuregulin phosphorylated CREB, a well-known down-stream transcription factor of PKA [24].

Regulatory relationships of Nrg1

• The utrophin promoter A is transcriptionally regulated in part by heregulin-mediated, extracellular signal-related kinase-dependent activation of the GABP(alpha/beta) transcription factor complex [1].
• Inhibition of CDK2 activity with either the specific CDK2 inhibitory peptide Tat-LFG or by RNA interference abolished neuregulin-induced AChRepsilon expression [19].
• It is likely that the secreted mature HRG activated the ErbB-2/3 receptors [25].
• DNA mobility shift assay revealed that HRG was able to induce PR binding to a progesterone response element (PRE) in C4HD and T47D cells [17].
• Taken together, these results suggest that the GA-binding protein alpha/beta complex of transcription factors binds and activates the utrophin promoter in response to heregulin-activated extracellular signal-regulated kinase in muscle cell cultures [26].

Other interactions of Nrg1

• The ErbB2 and ErbB3 receptors and their ligand, neuregulin-1, are essential for development of the sympathetic nervous system [14].
• Heregulin ameliorates the dystrophic phenotype in mdx mice [1].
• Neuregulin regulated CDK2 activity through coordinating phosphorylation of CDK2 on Thr-160, accumulation of CDK2 in the nucleus, and down-regulation of the CDK2 inhibitory protein p27 in the nucleus [19].
• Finally, we demonstrate here for the first time that HRG-activated MAPK can phosphorylate both human and mouse PR in vitro [17].
• In addition, we also observed a novel mechanism of regulation of CDK2 activity by a low molecular weight variant of cyclin E in response to NRG [19].

Analytical, diagnostic and therapeutic context of Nrg1

• As a first step toward understanding the physiological role of NDF, we performed in situ hybridization analyses to determine mRNA distribution in the mouse embryo and to map the gene to human karyotypes [27].
• Intraperitoneal injections of a small peptide encoding the epidermal growth factor-like region of heregulin ectodomain for 3 months in vivo resulted in up-regulation of utrophin, a marked improvement in the mechanical properties of muscle as evidenced by resistance to eccentric contraction mediated damage, and a reduction of muscle pathology [1].
• Western blot analysis showed activation of ErbB2 and ErbB3, suggesting a possible mode of action of extracellular HRG in mammary gland carcinomas [2].
• When NPs were induced to migrate and differentiate by adhesion of neurospheres to the substratum, the level of type III isoforms detected by RT-PCR and Western blot decreased in parallel with a reduction in Nrg-1 fluorescence intensity in differentiating astrocytes, neurons, and oligodendrocytes [20].
• Accordingly, site-directed mutagenesis of a single N-box motif in the utrophin gene promoter abolished the transcriptional response to heregulin [28].

References