Stephen K. Horrigan

A novel nuclear protein, 5qNCA (LOC51780) is a candidate for the myeloid leukemia tumor suppressor gene on chromosome 5 band q31

Interstitial deletion or loss of chromosome 5, del(5q) or −5, is a frequent finding in myeloid leukemias and myelodysplasias, suggesting the presence of a tumor suppressor gene within the deleted region. In our search for this gene, we identified a candidate, 5qNCA (LOC51780), which lies within a consistently-deleted segment of 5q31. 5qNCA expresses a 7.2-kb transcript with a 5286-bp open reading frame which is present at high levels in heart, skeletal muscle, kidney, placenta, and liver as well as CD34+ cells and AML cell lines. 5qNCA encodes a 191-kD nuclear protein which contains a highly-conserved C-terminus containing a zinc finger with the unique spacing Cys-X2-Cys-X7-His-X2-Cys-X2-Cys-X4-Cys-X2-Cys and a jmjC domain, which is often found in proteins that regulate chromatin remodeling. Expression of 5qNCA in a del(5q) cell line results in suppression of clonogenic growth. Preliminary sequence results in AML and MDS samples and cell lines has revealed a possible mutation in the KG-1 cell line resulting in a THR to ALA substitution that has not been found in over 100 normal alleles to date. We propose 5qNCA is a good candidate for the del(5q) tumor suppressor gene based on its predicted function and growth suppressive activities, and suggest that further mutational and functional study of this interesting gene is warranted.

LOCALIZATION OF THE CANDIDATE TUMOR SUPPRESSOR GENE ING1 TO HUMAN CHROMOSOME 13Q34

A novel gene ING1 was recently cloned and defined as a candidate tumor suppressor gene. Reduced expression and rearrangements of ING1 are found in several tumor cell lines, ING1 overexpression is associated with cell growth arrest and ING1 suppression promotes neoplastic transformation (1). Using radiation hybrid mapping technique ING1 was assigned to subtelomeric region of the long arm of human chromosome 13 (13q34) which is known to be frequently rearranged in squamous carcinomas of head and neck.

Chromosome 8 Losses in Colorectal Carcinoma: Localization and Correlation With Invasive Disease.

Background: Allelic losses from the short arm of chromosome 8 (8p) are frequent in a variety of epithelial malignancies. In colorectal cancer, there are two discrete regions of 8p loss of hterozygosity (LOH), suggesting the existence of two putative tumor suppressor genes. Previous studies have shown an association of 8p LOH with tumor invasiveness. To better define the deletion extent and the clinical significance of these losses, a series of 41 colorectal cancers were examined for 8p LOH and correlated with clinical features. Methods and Results: Paired normal and enriched tumor DNA from the same individual was typed by polymerase chain reaction for 11 microsatellite polymorphisms and scored as positive or negative for 8p LOH. Loss of 8p markers was observed in 44% of the cases. Most cases had large deletions, but several had localized interstitial losses, enabling specification of two nonoverlapping regions of LOH. The telomeric region of loss is defined by the markers D8S262 and D8S133 at 8p22, and the centromeric region is proximal to NEFL. Clinical, histopathologic, and molecular data were obtained and a significant correlation of 8p LOH with microinvasion (invasion of lymphatics, vessels, or perineurium, ascertained by light microscopy) (P=.01) and also with loss of chromosome arm 18q (P=.001) was found. Conclusions: An association of 8p allelic loss with poor outcome was demonstrated. The correlation between 8p loss and 18q loss suggests that 8p LOH is a late event in the multistep model of colorectal carcinogenesis. 8p LOH may provide a clinically useful prognostic marker in colorectal cancer, thereby warranting further testing. The involvement of two independent loci on 8p is confirmed, and the refined localization of these sites will contribute to the eventual identification of these genes, which appear to play an important role in the progression of epithelial malignancies.

Evidence for anticipation in autosomal dominant limb-girdle muscular dystrophy.

Anticipation, an increase in severity or decrease in age of onset (AO) inherent in the transmission of the disease gene from affected parent to affected child, has been increasingly described in human disease. To assess anticipation in a large kindred in which autosomal dominant limb-girdle muscular dystrophy (LGMD1A) is segregating, age of disease onset was collected from patient interviews of affected family members. A total of 25 parent-offspring pairs, in which the parents are three (3R), four (4R), or five (5R) generations removed from a common founding ancestor, were available for analysis. Life table analyses showed significant decreases in age at first reported symptoms in the offspring of the 3R (chi2=5.55, p=0.02) and 4R (chi2=7.81, p=0.005) parents. Pairwise analyses confirmed this decrease with a median decrease of 13 years in transmission to offspring from 3R parents and 18 years in transmission to offspring from 4R parents. The finding of anticipation in this pedigree suggests that the mutation in LGMD1A may be the result of the expansion of an unstable trinucleotide repeat.

Novel nuclear receptor coactivator is a candidate for the del(5q) Leukemia tumor suppressor gene

Abstract Interstitial deletion or loss of chromosome 5 is frequent in myeloid leukemias and dysplasias, suggesting the presence of a tumor suppressor gene (TSG) within the consistently-deleted region at 5q31. We report a novel gene at 5q31, 5qNCA, as a candidate for this TSG. 5qNCA spans 23 exons and produces a 7.4-kb transcript with a 5,286-kb open reading frame that is expressed in heart, skeletal muscle, lung, and placenta as well as CD34+ cells and AML cell lines. The gene contains a highly conserved C-terminus with putative transcriptional regulatory activity, a signature motif for a nuclear receptor co-activator, and a zinc finger (ZF). 5qNCA is homologous to TRIP8, human/murine hairless, KIAA0742, and drosophila CG815 in the ZF and transactivation domains. The ZF has the unique spacing CysX2-Cys-X7-His-X2-Cys-X2-Cys-X4-Cys-X2-Cys, which may define a new family, resembling both LIM and PHD ZF domains, which regulate chromatin structure and are often involved in leukemia. KG-1, an AML cell line with del(5q), shows a mutation in exon 6 resulting in a THR to ALA substitution of unknown significance; additional sequencing is in progress in clinical del(5q) samples. We propose 5qNCR as a likely candidate for the del(5q) TSG based on its protein homologies, expression, and mutation.

Mighty, But How Useful? The Emerging Role of Genetically Engineered Mice in Cancer Drug Discovery and Development

Studies on genetically engineered mouse models (GEMMs) have provided invaluable insights to our understanding of human tumors for nearly three decades. The ability to manipulate the murine genome with ever increasing sophistication has generated great expectations for their successful use in developing novel therapeutics. Indeed, GEMMs have shown remarkable power to faithfully recapitulate some key aspects of human tumorigenesis and therapy response. Yet, despite much enthusiasm generated during the early years of the new millennium, their use in drug discovery and development has remained limited. Economic, practical, licensing, historical, and regulatory considerations remain as hurdles to the robust utility of GEMMs in drug discovery and development as does the modest predictive abilities of any single model. Because cancer is a cellular and genetic disorder, advancing treatment options and cure rates will very likely continue to depend on the intelligent use of a combination of simple and complex experimental model systems, including biochemical, cell- and tissue-based and animal models. To date, the most pronounced impact that GEMMs have had on the biomedical industry has been in the areas of target and pathway validation, disease history elucidation, and the discovery and refinement of pharmacodynamic and toxicity biomarkers. There are also areas where GEMMs have tremendous potential but are currently underused, such as modeling metastatic disease spread, stem cell targeting, predictive marker testing, adaptive resistance modeling in vivo or ex vivo or the pharmacogenetic representation of heterogeneous patient populations.