ABSTRACT
gamma-heregulin is a recently described novel isoform of the heregulin/neuregulin class of EGF-like ligands that bind to and activate receptors of the ErbB family. Deregulated signaling through the heregulin-ErbB pathway is thought to be implicated in the development of a subset of human breast cancers. gamma-heregulin has been found to be expressed in the culture supernatant of MDA-MB-175, a breast carcinoma cell line. gamma-heregulin is characterized by the presence of a large N-terminal peptide extension that is not found in other heregulin isoforms. Here we report that this unique N-terminal extension of gamma-heregulin is identical to the N-terminus of DOC4, a product of a recently identified CHOP-dependent stress-induced gene. Human DOC4 and the heregulin-encoding genes map to different chromosomes and the MDA-MB-175 cell line contains a chromosomal translocation that leads to the fusion of DOC4 and HGL, on chromosomes 11 and 8, respectively. Thus, gamma-heregulin is a product of a mutant fusion gene and not a bona fide normal isoform. We speculate that the mutation may be selected for by virtue of its ability to activate ErbB signaling through the production of an autocrine ligand.
Subject(s)
Breast Neoplasms/genetics , Carcinoma/genetics , Carrier Proteins/genetics , Chromosomes, Human, Pair 11/genetics , Chromosomes, Human, Pair 8/genetics , Neuregulin-1/genetics , Nuclear Proteins/genetics , Oncogene Proteins, Fusion/genetics , Translocation, Genetic , Breast Neoplasms/pathology , Carcinoma/pathology , Chromosomes, Human, Pair 11/ultrastructure , Chromosomes, Human, Pair 8/ultrastructure , Female , Gene Expression Regulation, Neoplastic , Humans , In Situ Hybridization, Fluorescence , Membrane Proteins , Receptor, ErbB-2/physiology , Signal Transduction , Tumor Cells, CulturedABSTRACT
LOH11A is a region of Chromosome (Chr) 11p15.5 where 75% of lung cancers show loss of heterozygosity (LOH). Clinical and cell biological studies suggest that LOH11A contains a tumor/metastasis suppressor gene. We have mapped this region (650 kb) using overlapping genomic P1/PAC/BAC clones, and one of the genes that we have identified is RRM1. This gene encodes the large subunit (M1) of ribonucleotide reductase, the heterodimeric enzyme that catalyzes the rate-limiting step in deoxyribonucleotide synthesis. By comparing our genomic sequences with the previously published cDNA, we have found that the human gene is composed of 19 exons. It is oriented telomere to centromere and is Alu rich. In order to verify that RRM1 maps within the boundaries of LOH11A, we assessed the frequency of LOH at a SacI polymorphism within intron IX of the gene. We observed LOH in 48% (15/31) of informative lung tumor specimens. To determine whether RRM1 was mutated in tumors, SSCP analysis of the 19 RRM1 exons was performed. No mutations were revealed in 12 pairs of normal and tumor DNA samples. Immunoblots on protein extracts from normal/tumor pairs indicated that a protein of the expected size was present in both. Our conclusion is that RRM1 lies within the LOH11A region, but that its exons are not mutated in tumors. The potential for RRM1 to act as a tumor suppressor is discussed.
Subject(s)
Lung Neoplasms/enzymology , Lung Neoplasms/genetics , Ribonucleotide Reductases/genetics , Base Sequence , Chromosomes, Human, Pair 11/genetics , DNA Primers/genetics , DNA, Complementary/genetics , Exons , Genes, Tumor Suppressor , Humans , Introns , Loss of Heterozygosity , Molecular Sequence Data , Mutation , Polymorphism, Single-Stranded Conformational , Protein Conformation , Restriction Mapping , Ribonucleotide Reductases/chemistry , Tumor Cells, CulturedABSTRACT
Cells modify their gene expression pattern in response to stress signals emanating from the endoplasmic reticulum (ER). The well-characterized aspect of this response consists of the activation of genes that encode protein chaperones and other ER resident proteins, and is conserved between mammals and yeast. In mammalian cells, however, ER stress also activates other pathways, including the expression of the transcription factor CHOP/GADD153 and its downstream target genes. ER stress is also linked to the development of programmed cell death, a phenomenon in which CHOP plays an important role. Here we report on the cloning of a murine homolog of yeast IRE1, an essential upstream component of the ER stress-response in yeast. The mammalian Ire1 is located in the ER membrane and its over-expression in mammalian cells activates both the endogenous ER chaperone GRP78/BiP and CHOP-encoding genes. Over-expression of a dominant-negative form of Ire1 blocks the induction of GRP78/BiP and CHOP in response to the ER stress induced by tunicamycin treatment. Over-expression of murine Ire1 also leads to the development of programmed cell death in transfected cells. These results indicate that a single upstream component, Ire1, plays a role in multiple facets of the ER stress-response in mammalian cells.
Subject(s)
Adaptation, Biological , CCAAT-Enhancer-Binding Proteins , Endoplasmic Reticulum/metabolism , Homeostasis , Membrane Glycoproteins/metabolism , Membrane Proteins , Protein Serine-Threonine Kinases/genetics , Amino Acid Sequence , Animals , COS Cells , Chromosome Mapping , DNA, Complementary/genetics , DNA-Binding Proteins/biosynthesis , Endoplasmic Reticulum Chaperone BiP , Gene Library , Membrane Glycoproteins/genetics , Mice , Molecular Sequence Data , Protein Folding , Recombinant Proteins/metabolism , Sequence Homology, Amino Acid , Signal Transduction , Stress, Physiological , Transcription Factor CHOP , Transcription Factors/biosynthesisABSTRACT
Lung cancers are a heterogeneous group of tumors broadly classified as small cell or non-small cell lung cancers. In each case, numerous DNA mutations precede tumor formation, resulting in the activation of growth stimulatory genes and the loss of tumor suppressor genes. The known cellular functions of the tumor suppressor genes most commonly affected in lung cancer are reviewed herein, including the retinoblastoma (Rb) gene on chromosome 13q14, the p53 gene on 17p13, and the cyclin-dependent kinase inhibitor (CDKN2) gene on 9p21. The chromosomal locations for other potential tumor suppressor genes are on chromosomes 3p, 9p, and 11p. Candidate genes in these regions include the von Hippel-Lindau (VHL) gene at 3p25, the ubiquitin-activating enzyme homologue (UBE1L at 3p21, the genes for the dinucleoside polyphosphate hydrolase FHIT and receptor protein-tyrosine phosphatase gamma PTPRG at 3p14.2, the genes for tropomyosin beta (TM1) and a talin homologue (talin) at 9p21, and the H-ras gene at 11p15.