[Show abstract][Hide abstract] ABSTRACT: Genomic imprinting is the biological process whereby a gene or genomic domain exists in a state of epigenetic differentiation that depends upon its parent of origin. Importantly, the establishment and propagation of these parent-specific genomic conformations does not alter the primary DNA sequence comprised of A, C, G, and T nucleotides. Genomic imprints may be covalent (DNA methylation) or non-covalent (DNA-protein and DNA-RNA interactions, genomic localization in nuclear space), and the process of imprinting encompasses the specialized nuclear enzymatic machinery that maintains parental epigenetic markings throughout the cell cycle. Because of genomic imprinting, the parent of origin of homologous genetic alleles in diploid individuals can be determined in the absence of DNA sequence polymorphisms and without recourse to parental DNA samples. As illustrated in Figure 1, alleles of imprinted genes look and behave differently, as determined by parent of origin.
[Show abstract][Hide abstract] ABSTRACT: The mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) encodes for a multifunctional receptor involved in lysosomal enzyme trafficking, fetal organogenesis, cytotoxic T cell-induced apoptosis and tumor suppression. The purpose of this investigation was to determine if the M6P/IGF2R tumor suppressor gene is mutated in human head and neck cancer, and if allelic loss is associated with poor patient prognosis.
M6P/IGF2R loss of heterozygosity in locally advanced squamous cell carcinoma of the head and neck was assessed with six different gene-specific nucleotide polymorphisms. The patients studied were enrolled in a phase 3 trial of twice daily radiotherapy with or without concurrent chemotherapy; median follow-up for surviving patients is 76 months.
M6P/IGF2R was polymorphic in 64% (56/87) of patients, and 54% (30/56) of the tumors in these informative patients had loss of heterozygosity. M6P/IGF2R loss of heterozygosity was associated with a significantly reduced 5 year relapse-free survival (23% vs. 69%, p = 0.02), locoregional control (34% vs. 75%, p = 0.03) and cause specific survival (29% vs. 75%, p = 0.02) in the patients treated with radiotherapy alone. Concomitant chemotherapy resulted in a better outcome when compared to radiotherapy alone only in those patients whose tumors had M6P/IGF2R loss of heterozygosity.
This study provides the first evidence that M6P/IGF2R loss of heterozygosity predicts for poor therapeutic outcome in patients treated with radiotherapy alone. Our findings also indicate that head and neck cancer patients with M6P/IGF2R allelic loss benefit most from concurrent chemotherapy.
[Show abstract][Hide abstract] ABSTRACT: Mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) tumor suppressor- gene mutation is an early event in human hepatocellular carcinoma (HCC) formation in the United States, but its role in hepatocarcinogenesis in Japan is unclear. We therefore determined M6P/IGF2R mutation frequency in HCCs from patients who resided in the southern, central, and northern regions of Japan. Ten single nucleotide polymorphisms were used to identify HCCs and dysplastic liver nodules with M6P/IGF2R loss of heterozygosity. The retained allele in these tumors was also assessed for point mutations and deletions in the M6P/IGF2R ligand binding domains by direct sequencing of polymerase chain reaction (PCR) amplified DNA products. Fifty-eight percent (54 of 93) of the patients were heterozygous at the M6P/IGF2R locus, and 67% (43 of 64) of the HCCs and 75% (3 of 4) of the dysplastic nodules had loss of heterozygosity. The remaining allele in 21% of the HCCs contained either M6P/IGF2R missense mutations or deletions, whereas such mutations were not found in the dysplastic lesions. In conclusion, M6P/IGF2R is mutated in HCCs from throughout Japan with a frequency similar to that in the United States. Loss of heterozygosity in dysplastic liver nodules provides additional evidence that M6P/IGF2R haploid insufficiency is an early event in human hepatocarcinogenesis.
[Show abstract][Hide abstract] ABSTRACT: M6P/IGF2R imprinting first appeared approximately 150 million years ago following the divergence of prototherian from therian mammals. Although M6P/IGF2R is clearly imprinted in opossums and rodents, its imprint status in humans remains ambiguous. It is also still unknown if M6P/IGF2R imprinting was an ancestral mammalian epigenotype or if it evolved convergently. We report herein that M6P/IGF2R is imprinted in Artiodactyla, as it is in Rodentia and Marsupialia, but that it is not imprinted in Scandentia, Dermoptera and Primates, including ringtail lemurs and humans. These results are most parsimonious with a single ancestral origin of M6P/IGF2R imprinting followed by a lineage-specific disappearance of M6P/IGF2R imprinting in Euarchonta. The absence of M6P/IGF2R imprinting in extant primates, due to its disappearance from the primate lineage over 75 million years ago, demonstrates that imprinting at this locus does not predispose to human disease. Moreover, the divergent evolution of M6P/IGF2R imprinting predicts that the success of in vitro embryo procedures such as cloning may be species dependent.
Human Molecular Genetics 09/2001; · 7.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The three living monophyletic divisions of Class Mammalia are the Prototheria (monotremes), Metatheria (marsupials), and
Eutheria (`placental' mammals). Determining the sister relationships among these three groups is the most fundamental question
in mammalian evolution. Phylogenetic comparison of these mammals by either anatomy or mitochondrial DNA has resulted in two
conflicting hypotheses, Theria and Marsupionta, and has fueled a ``genes versus morphology'' controversy. We have cloned and
analyzed a large nuclear gene, the mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R), from representatives of all three mammalian groups, including platypus, echidna, opossum, wallaby, hedgehog, mouse, rat,
rabbit, cow, pig, bat, tree shrew, colugo, ringtail lemur, and human. Statistical analysis of this nuclear gene unambiguously
supports the morphology-based Theria hypothesis that excludes monotremes from a clade of marsupials and eutherians. The M6P/IGF2R was also able to resolve the finer structure of the eutherian mammalian family tree. In particular, our analyses support
sister group relationships between lagomorphs and rodents, and between the primates and Dermoptera. Statistical support for
the grouping of the hedgehog with Feruungulata and Chiroptera was also strong.
[Show abstract][Hide abstract] ABSTRACT: Genomic imprinting is a method of gene regulation whereby a gene is expressed in a parent-of-origin-dependent fashion; however, it is hypothesized that imprinting should not occur in oviparous taxa such as birds. Therefore, we examined the allelic expression of two genes in the chicken that are reciprocally imprinted in most mammals, mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) and insulin-like growth factor 2 (IGF2). Single nucleotide polymorphisms were identified in these genes, and cDNA was prepared from several tissues of embryos heterozygous for these polymorphisms. Both alleles of M6P/IGF2R and IGF2 were expressed in all tissues examined by RT-PCR. Since the expression of these genes was independent of the parent from which they were inherited, we conclude that neither M6P/IGF2R nor IGF2 are imprinted in the chicken.
Development Genes and Evolution 05/2001; 211(4):179-83. · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Imprinted gene identification in animals has been limited to eutherian mammals, suggesting a significant role for intrauterine fetal development in the evolution of imprinting. We report herein that M6P/IGF2R is not imprinted in monotremes and does not encode for a receptor that binds IGF2. In contrast, M6P/IGF2R is imprinted in a didelphid marsupial, the opossum, but it strikingly lacks the differentially methylated CpG island in intron 2 postulated to be involved in imprint control. Thus, invasive placentation and gestational fetal growth are not required for imprinted genes to evolve. Unless there was convergent evolution of M6P/ IGF2R imprinting and receptor IGF2 binding in marsupials and eutherians, our results also demonstrate that these two functions evolved in a mammalian clade exclusive of monotremes.
[Show abstract][Hide abstract] ABSTRACT: In addition to the intracellular sorting of lysosomal enzymes, the mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) plays a critical role in regulating the bioavailability of extracellular proteolytic enzymes and growth factors. It has also been shown to be mutated in a number of human cancers, and to suppress cancer cell growth. The purpose of this study was to determine if the M6P/IGF2R is mutated in lung cancer, a leading cause of cancer death worldwide. Archival pathology specimens were obtained on 22 patients with newly diagnosed, untreated squamous cell carcinoma of the lung. Two polymorphisms in the 3'-untranslated region of the M6P/IGF2R were used to screen lung tumors for loss of heterozygosity (LOH) by PCR amplification of DNA. Nineteen of 22 (86%) patients were informative (heterozygous), and 11/19 (58%) squamous cell carcinomas of the lung had LOH at the M6P/IGF2R locus. The remaining allele in 6/11 (55%) LOH patients contained mutations in either the mannose 6-phosphate or the IGF2 binding domain of the M6P/IGF2R. Thus, the M6P/IGF2R is mutated frequently in squamous cell carcinoma of the lung, providing further support for its function as a tumor suppressor.
[Show abstract][Hide abstract] ABSTRACT: Polymorphisms have been identified in proto-oncogenes and tumor suppressor genes that predispose people to cancer. Recent evidence indicates that genomic imprinting, an epigenetic form of gene regulation that results in uniparental gene expression, can also function as a cancer predisposing event. Thus, cancer susceptibility is increased by both Mendelian inherited genetic and non-Mendelian inherited epigenetic events. Consequently, chemical and physical agents cannot only induce cancer through the formation of genetic mutations but also through epigenetic changes that result in the inappropriate expression of imprinted proto-oncogenes and tumor suppressor genes. The role of genomic imprinting in carcinogenesis and cancer susceptibility is examined in this review.
Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 02/1999; 436(1):59-67. · 3.90 Impact Factor