Low frequency of p57KIP2 mutation in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an autosomal dominant disorder of increased prenatal growth and predisposition to embryonal cancers such as Wilms tumor. BWS is thought to involve one or more imprinted genes, since some patients show paternal uniparental disomy, and others show balanced germ-line chromosomal rearrangements involving the maternal chromosome. We previously mapped BWS, by genetic linkage analysis, to 11p15.5, which we and others also found to contain several imprinted genes; these include the gene for insulin-like growth factor II (IGF2) and H19, which show abnormal imprint-specific expression and/or methylation in 20% of BWS patients, and p57KIP2, a cyclin-dependent kinase inhibitor, which we found showed biallelic expression in one of nine BWS patients studied. In addition, p57KIP2 was recently reported to show mutations in two of nine BWS patients. We have now analyzed the entire coding sequence and intron-exon boundaries of p57KIP2 in 40 unrelated BWS patients. Of these patients, only two (5%) showed mutations, both involving frameshifts in the second exon. In one case, the mutation was transmitted to the proband's mother, who was also affected, from the maternal grandfather, suggesting that p57KIP2 is not imprinted in at least some affected tissues at a critical stage of development and that haploinsufficiency due to mutation of either parental allele may cause at least some features of BWS. The low frequency of p57KIP2 mutations, as well as our recent discovery of disruption of the K(v)LQT1 gene in patients with chromosomal rearrangements, suggest that BWS can involve disruption of multiple independent 11p15.5 genes.     

Altered cell differentiation and proliferation in mice lacking p57KIP2 indicates a role in Beckwith-Wiedemann syndrome

Mice lacking the imprinted Cdk inhibitor p57(KIP2) have altered cell proliferation and differentiation, leading to abdominal muscle defects; cleft palate; endochondral bone ossification defects with incomplete differentiation of hypertrophic chondrocytes; renal medullary dysplasia; adrenal cortical hyperplasia and cytomegaly; and lens cell hyperproliferation and apoptosis. Many of these phenotypes are also seen in patients with Beckwith-Wiedemann syndrome, a pleiotropic hereditary disorder characterized by overgrowth and predisposition to cancer, suggesting that loss of p57(KIP2) expression may play a role in the condition.     

p57KIP2 targeted disruption and Beckwith-Wiedemann syndrome: is the inhibitor just a contributor?

Beckwith-Wiedemann syndrome is a human congenital disorder characterized by a wide variety of growth abnormalities, including developmental defects and predisposition to certain tumors. Genetic evidence has suggested a role for p57KIP2, a member of a family of cell cycle inhibitory genes, in Beckwith-Wiedemann syndrome. Two independent groups have reported the generation and characterization of mice lacking functional p57KIP2. These mice demonstrate a number of abnormal phenotypes which overlap with, although do not completely recapitulate, Beckwith-Wiedemann syndrome. These findings advance the molecular characterization of a human disorder, and provide insight into the interplay between regulation of cell division and development.     

Chromosome 11p15.5 regional imprinting: comparative analysis of KIP2 and H19 in human tissues and Wilms' tumors

The imprinted H19 gene is frequently inactivated in Wilms' tumors (WTs) either by chromosome 11p15.5 loss of heterozygosity (LOH) or by hypermethylation of the maternal allele and it is possible that there might be coordinate disruption of imprinting of multiple 11p15.5 genes in these tumors. To test this we have characterized total and allele-specific mRNA expression levels and DNA methylation of the 11p15.5 KIP2 gene in normal human tissues, WTs and embryonal rhabdomyosarcoma (RMS). Both KIP2 alleles are expressed but there is a bias with the maternal allele contributing 70-90% of mRNA. Tumors with LOH show moderate to marked reductions in KIP2 mRNA relative to control tissues and residual mRNA expression is from the imprinted paternal allele. Among WTs without LOH most cases with H19 inactivation also have reduced KIP2 expression and most cases with persistent H19 expression have high levels of KIP2 mRNA. In contrast to the extensive hypermethylation of the imprinted H19 allele, both KIP2 alleles are hypomethylated and WTs with biallelic H19 hypermethylation lack comparable hypermethylation of KIP2 DNA. 5-aza-2'-deoxycytidine (aza-C) increases H19 expression in RD RMS cells but does not activate KIP2 expression. These data indicate coordinately reduced expression of two linked paternally imprinted genes in most WTs and also suggest mechanistic differences in the maintenance of imprinting at these two loci.     

Clinicopathologic implications of MDM2, p53 and K-ras gene alterations in osteosarcomas: MDM2 amplification and p53 mutations found in progressive tumors

The role of rapidly growing mycobacteria in the pathogenesis of pulmonary disease is being increasingly recognized; however, the clinical significance of these mycobacteria in patients with underlying malignancy has not been well studied. Over a 6-year period, 37 cancer patients with rapidly growing mycobacteria isolated from respiratory specimens were identified at our center. Mycobacterium chelonae group was isolated in 24 cases and Mycobacterium fortuitum in 13 cases. Of the 24 cases with cultures yielding Mycobacterium chelonae group, eight met the study criteria for infection and were determined to be clinically significant, whereas only one of the Mycobacterium fortuitum isolates was determined to represent infection. An average of two antimicrobial agents were used for treatment, most commonly clarithromycin, ciprofloxacin, and trimethoprim/sulfamethoxazole. Although the isolation of rapidly growing mycobacteria represents colonization in most cases, these bacteria, especially the Mycobacterium chelonae group, may cause pulmonary disease in cancer patients. The clinical and radiological findings are usually non-specific in this population, and patients with respiratory cultures yielding rapidly growing mycobacteria should be assessed carefully to distinguish infection from colonization. Effective therapy can be provided with oral regimens that include at least two antibiotics to which the organism is susceptible.     

Loss of expression or mutations in the p73 tumour suppressor gene are not involved in the pathogenesis of malignant melanomas

BACKGROUND: The authors present their study on oncologic and functional results of supracricoid partial laryngectomies (SPL) performed on 149 patients between January 1984 and December 1995. METHODS: Cricohyoidopexy (CHP) was carried out on 98 patients and cricohyoidoepiglottopexy (CHEP) on 51 patients. The patients were divided into two groups. The first group included those operated on between January 1984 and December 1992 and who therefore had a minimum follow-up period of 3 years. The second group included those operated on after December 1992 and who therefore had a follow-up period of less than 3 years. The statistical evaluation of this second group was carried out using an actuarial method according to Kaplan-Meier. RESULTS: In the first group, survival rate (regarding disease-related deaths) was 94% (95/101), whereas in the second group, survival rate was 95%. There were 9 recurrences in the 149 patients (6.71%), B of which occurred after CHP (6 for tumor [T] and 2 for node [N]) and 1 (for T) after CHEP. Three of the 6 recurrences for T after CHP occurred in the hypopharynx, 2 in the peristomal area, and 1 in the arytenoid area. The only recurrence for T after CHEP occurred in the paraglottic area. Decannulation was carried out in 85.7% of CHP patients (84/98) and in 98% of CHEP patients (50/51). The nasogastric tube was kept in position for an average of 28 days (range, 15-90 days) in the CHP patients and 15 days (range, 9-90 days) in the CHEP patients. Swallowing was excellent; only a small number of patients (n = 21) were forced to assume a particular posture during meals. Phoniatric controls performed on 104 patients also showed adequate speech recovery. CONCLUSIONS: If the indications are applied scrupulously, CHEP is a valid alternative to partial laryngeal surgery and CHP is a possible alternative to total laryngectomy in the treatment of glottic and supraglottic tumors.     

Release of cell cycle constraints in mouse melanocytes by overexpressed mutant E2F1E132, but not by deletion of p16INK4A or p21WAF1/CIP1

Compared to normal melanocytes, melanoma cell lines exhibit overexpression of hyperphosphorylated retinoblastoma tumor suppressor protein (Rb) or a marked decrease in, or lack of, expression of Rb. Hyperphosphorylation of Rb results in increased E2F-mediated transactivation of target genes and cell cycle progression. Using a combination of gene disruption and ectopic expression in growth factor-dependent mouse melanocytes, we studied the roles of E2F1 and the p16INK4A and p21WAF1/CIP1 CKIs (cyclin dependent kinase inhibitors) in the acquisition of TPA (12-O-tetradecanoyl phorbol-13-acetate)-independent growth in culture, a hallmark of melanomas. Surprisingly, melanocytes from p16INK4A- or p21WAF1/CIP1-null mice remained TPA-dependent, and disruption of p21WAF1/CIP1 accelerated cell death in the absence of this mitogen. Disruption of E2F1 had the most profound effect on melanocyte growth, resulting in a fourfold decrease in growth rate in the presence of TPA. Furthermore, enforced overexpression of the DNA-binding-defective E2F1E132 mutant conferred TPA-independence upon melanocytes and was associated with sequestration of Rb and constitutive expression of E2F1 target genes, including p21WAF1/CIP1. We conclude that neutralization of Rb by E2F1E132, but not the disruption of p16INK4A or p21WAF1/CIP1, resulted in the accumulation of free E2F and cell cycle progression. Thus, mechanisms other than the loss of p16INK4A or p21WAF1/CIP1 that activate E2F may play an important role in melanomas.     

Intracellular coexpression of epidermal growth factor receptor, Her-2/neu, and p21ras in human breast cancers: evidence for the existence of distinctive patterns of genetic evolution that are common to tumors from different patients

Multiparameter flow cytometry studies were performed on cells from the primary tumors of 94 patients with breast cancer. Correlated cellular measurements of cell DNA content, Her-2/neu, epidermal growth factor receptor (EGFR), and p21ras levels were performed on each of 5,000 to 100,000 cells from each tumor. When criteria for positivity were matched with those in common use for immunohistochemical studies, 28 of 94 (30%) breast cancers were classified as positive for Her-2/neu overexpression. When similar criteria were applied to the EGFR measurements, 23 of 94 (24%) cases were classified as positive for EGFR overexpression. Similarly, 23 of 94 (24%) cases were classified as positive for p21ras overexpression. By conventional flow cytometric criteria for DNA ploidy, 24 cases were diploid, 28 were tetraploid, and 42 were aneuploid. When the measurements were treated as separate sets of data, the only statistically significant correlations noted were the high frequency of diploid tumors, which did not overexpress any of the three oncogenes studied (P < 0.05), and an association between Her-2/neu overexpression and aneuploidy (P < 0.03). When the data were treated as correlated intracellular measurements, 90 of the 94 tumors studied contained a population of cells in which the intracellular levels of Her-2/neu expression were directly correlated with the levels of EGFR expression in the same cells. The ratio of Her-2/neu molecules to EGFR molecules in the same cells exceeded 1 in the majority of tetraploid and aneuploid cases and was close to or less than 1 in the majority of diploid cases. In nearly all tumors, p21ras overexpression was observed only in cells that overexpressed Her-2/neu, EGFR, or both, and p21ras levels per cell were more closely correlated with levels of EGFR per cell in the same cells than with Her-2/neu levels per cell. The data are consistent with a model in which heterodimerization of Her-2/neu and EGFR in individual cells is achieved by one of several genetic evolutionary pathways, all of which commonly lead to p21ras overexpression. The two major genetic evolutionary pathways identified in this study are an aneuploid, Her-2/neu overexpression-driven pathway seen in 59 of 94 tumors, and a diploid, EGFR overexpression-driven pathway seen in 19 of 94 tumors. All tumors with Her-2/neu:EGFR ratios greater than 2 contained an infiltrating ductal carcinoma component, whereas all infiltrating pure lobular carcinomas had Her-2/ neu:EGFR ratios that were less than 2. All of the genetic evolutionary pathways identified in this study were represented among the 11 tumors from patients who experienced early tumor recurrences.     

The Knights of the Round Table hypothesis of tumour suppressor gene function--noble sacrifice or sexual dalliance: genes, including p53, BRCA1/2 and RB have evolved by horizontal and vertical transmission of mating factor genes and are involved in gametogenesis, implantation, development and tumourigenesis

The genes involved in negative cell cycle regulation and familial tumour susceptibility including APC, BRCA, p53, RB, WT1 are unique and have no homologies with other genes. Our hypothesis suggests they originated from mating factor genes, which halted cell division in response to stress to generate genetic diversity by sexual mechanisms. Some have evolved principally by vertical transmission (mismatch repair), others by horizontal transmission via mobile elements, predominantly in oocytes. We demonstrate amplification in human extra-embryonic tissues in fetus and mother in implantation; in the developing fetus, differing tissue-specific patterns are seen, especially between testis and ovary. We suggest that the fetus is susceptible to maternal transmission of infections including CMV, malaria, trypanosomes, whose sequences occur within these genes. In head and neck cancers, we demonstrate specific patterns of loss or instability involving up to seven different TSG. We suggest mechanisms of tumourigenesis involve transposable elements and episome formation, leading to loss of negative cell cycle regulation and exit from G0.