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.     

Cyclin-dependent kinase inhibitor p21 modulates the DNA primer-template recognition complex

The p21 protein, a cyclin-dependent kinase (CDK) inhibitor, is capable of binding to both cyclin-CDK and the proliferating cell nuclear antigen (PCNA). Through its binding to PCNA, p21 can regulate the function of PCNA differentially in replication and repair. To gain an understanding of the precise mechanism by which p21 affects PCNA function, we have designed a new assay for replication factor C (RFC)-catalyzed loading of PCNA onto DNA, a method that utilizes a primer-template DNA attached to agarose beads via biotin-streptavidin. Using this assay, we showed that RFC remains transiently associated with PCNA on the DNA after the loading reaction. Addition of p21 did not inhibit RFC-dependent PCNA loading; rather, p21 formed a stable complex with PCNA on the DNA. In contrast, the formation of a p21-PCNA complex on the DNA resulted in the displacement of RFC from the DNA. The nonhydrolyzable analogs of ATP, adenosine-5'-O-(3-thiotriphosphate) (ATPgammaS) and adenyl-imidodiphosphate, each stabilized the primer recognition complex containing RFC and PCNA in the absence of p21. RFC in the ATPgammaS-activated complex was no longer displaced from the DNA by p21. We propose that p21 stimulates the dissociation of the RFC from the PCNA-DNA complex in a process that requires ATP hydrolysis and then inhibits subsequent PCNA-dependent events in DNA replication. The data suggest that the conformation of RFC in the primer recognition complex might change on hydrolysis of ATP. We also suggest that the p21-PCNA complex that remains attached to DNA might function to tether cyclin-CDK complexes to specific regions of the genome.     

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.     

Cyclin D- and E-dependent kinases and the p57(KIP2) inhibitor: cooperative interactions in vivo

This study examines in vivo the role and functional interrelationships of components regulating exit from the G1 resting phase into the DNA synthetic (S) phase of the cell cycle. Our approach made use of several key experimental attributes of the developing mouse lens, namely its strong dependence on pRb in maintenance of the postmitotic state, the down-regulation of cyclins D and E and up-regulation of the p57(KIP2) inhibitor in the postmitotic lens fiber cell compartment, and the ability to target transgene expression to this compartment. These attributes provide an ideal in vivo context in which to examine the consequences of forced cyclin expression and/or of loss of p57(KIP2) inhibitor function in a cellular compartment that permits an accurate quantitation of cellular proliferation and apoptosis rates in situ. Here, we demonstrate that, despite substantial overlap in cyclin transgene expression levels, D-type and E cyclins exhibited clear functional differences in promoting entry into S phase. In general, forced expression of the D-type cyclins was more efficient than cyclin E in driving lens fiber cells into S phase. In the case of cyclins D1 and D2, ectopic proliferation required their enhanced nuclear localization through CDK4 coexpression. High nuclear levels of cyclin E and CDK2, while not sufficient to promote efficient exit from G1, did act synergistically with ectopic cyclin D/CDK4. The functional differences between D-type and E cyclins was most evident in the p57(KIP2)-deficient lens wherein cyclin D overexpression induced a rate of proliferation equivalent to that of the pRb null lens, while overexpression of cyclin E did not increase the rate of proliferation over that induced by the loss of p57(KIP2) function. These in vivo analyses provide strong biological support for the prevailing view that the antecedent actions of cyclin D/CDK4 act cooperatively with cyclin E/CDK2 and antagonistically with p57(KIP2) to regulate the G1/S transition in a cell type highly dependent upon pRb.     

High prognostic significance of Mdm2/p53 co-overexpression in soft tissue sarcomas of the extremities

Soft tissue sarcomas are a heterogeneous group of neoplasms with various histological subtypes. Up to now, no individual causal molecular markers for prognosis and therapeutic success have been identified. A tumorigenic connection between the oncogene product Mdm2 and tumor suppressor p53 is generally accepted, but their possible clinical relevance has not yet been investigated sufficiently in soft tissue sarcoma. In 86 primary soft tissue sarcoma of the extremities (RO-resected, T1/2 N0 M0), Mdm2 and p53 overexpression were investigated by immunohistochemistry. The results were adjusted to clinico-pathological characteristics and evaluated for their prognostic relevance by multivariate analysis. In Cox's multivariate analysis with stratification of Mdm2 to p53 results, we determined four groups which had different prognostic values for relapse-free and overall survival (Mdm2-/p53- < Mdm2-/p53+ < Mdm2+/p53- < Mdm2+/p53+). The most striking finding was a relative risk (rr) for overall survival of 18.77 (P=0.006) for patients with Mdm2/p53 co-overexpression (n=40). It is noticeably higher than the additive risk from both factors. Coincident Mdm2/p53 overexpression is an independent molecular marker with the highest prognostic relevance described for soft tissue sarcoma. Thus, a high risk sarcoma group has been defined which we believe requires alternative therapeutic approaches.     

E-Cadherin-dependent growth suppression is mediated by the cyclin-dependent kinase inhibitor p27(KIP1)

Recent studies have demonstrated the importance of E-cadherin, a homophilic cell-cell adhesion molecule, in contact inhibition of growth of normal epithelial cells. Many tumor cells also maintain strong intercellular adhesion, and are growth-inhibited by cell- cell contact, especially when grown in three-dimensional culture. To determine if E-cadherin could mediate contact-dependent growth inhibition of nonadherent EMT/6 mouse mammary carcinoma cells that lack E-cadherin, we transfected these cells with an exogenous E-cadherin expression vector. E-cadherin expression in EMT/6 cells resulted in tighter adhesion of multicellular spheroids and a reduced proliferative fraction in three-dimensional culture. In addition to increased cell-cell adhesion, E-cadherin expression also resulted in dephosphorylation of the retinoblastoma protein, an increase in the level of the cyclin-dependent kinase inhibitor p27(kip1) and a late reduction in cyclin D1 protein. Tightly adherent spheroids also showed increased levels of p27 bound to the cyclin E-cdk2 complex, and a reduction in cyclin E-cdk2 activity. Exposure to E-cadherin-neutralizing antibodies in three-dimensional culture simultaneously prevented adhesion and stimulated proliferation of E-cadherin transfectants as well as a panel of human colon, breast, and lung carcinoma cell lines that express functional E-cadherin. To test the importance of p27 in E-cadherin-dependent growth inhibition, we engineered E-cadherin-positive cells to express inducible p27. By forcing expression of p27 levels similar to those observed in aggregated cells, the stimulatory effect of E-cadherin-neutralizing antibodies on proliferation could be inhibited. This study demonstrates that E-cadherin, classically described as an invasion suppressor, is also a major growth suppressor, and its ability to inhibit proliferation involves upregulation of the cyclin-dependent kinase inhibitor p27.     

Therapeutic use of carminomycin in soft tissue sarcomas

Under endoscopic control, biopsy specimens were taken from the oxyntic gland area of the stomach before and after administration of pentagastrin, synthetic secretin, and 13-norleucine motilin (13-nle-motilin), respectively. In 29 volunteers, the basal rate of 14C-leucine incorporation into mucosal protein averaged 41.2 +/- 7.7 X 103 cpm/mg protein (mean +/- S.D.). One and 4 hours after s.c. administration of pentagastrin (6 mug/kg body weight), values were significantly increased (p less than 0.05) by 18.9 and 21.8%, respectively, with respect to the basal level. One hour after an intravenous shot of 2 CU per kg body weight of secretin, gastric mucosal protein synthetis was not substantially inhibited, whereas a 1-hour continuous i.v. infusion of 13-nle-motilin (0.4 mug/kg body weight, hr) significantly decreased 14C-leucine incorporation rates by 17.5% (p less than 0.05). In contrast to rats, 1 hour after s.c. pentagastrin, protein synthesis in human duodenal mucosa was not altered. From these results it may be concluded that pentagastrin has a trophic influence on gastric mucosa in man. Moreover, the data presented are compatible with the hypothesis that gastrin and motilin may be involved in the regulation of human gastric mucosal protein synthesis.     

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.     

Morphology and molecular biology of malignant soft tissue sarcomas

Malignant soft tissue tumors are classified and named according to cellular differentiation and thus the non-neoplastic soft tissue they imitate. The topical WHO classification already comprises more than 140 entities and tumor subtypes, but the process of defining new tumor variants will go on. Questions of nomenclature are discussed briefly with laying special emphasis on the non-undisputed concept of malignant fibrous histiocytomas. Without doubt, this diagnosis is made too frequently by which it has become to a collective name for unclassifiable pleomorphic sarcomas. For the time being nobody is able to say whether or not the malignant fibrous histiocytoma will remain an entity. Likely, fibrosarcomas and hemangiopericytomas are defined as exclusion diagnosis, as well. The diagnosis of malignant soft tissue tumors is based on recognizing the cellular line of differentiation. This is frequently possible at light microscopic level, sometimes additional diagnostic methods are required. The most important adjunct method is immunohistochemistry. Because aberrant differentiations and unexpected immunohistochemical reactions are known the use of a panel of antibodies is necessary. In the last years soft tissue tumors has increasingly been characterized by molecular biological methods. The results are of significance for understanding sarcoma pathogenesis and may be used for diagnosis, as well. Chromosome translocations are explained and rhabdomyosarcomas are taken as example for demonstrating the diagnostic significance of molecular biological/cytogenetic findings. Molecular biology may also aid in defining the histopathologic features of an entity as shown for intraabdominal desmoplastic small cell tumors. Eventually, heterogeneity in soft tissue sarcomas is addressed and discussed in view of its importance for diagnosis, classification and therapy as well as for development of sarcoma progression.     

Combined modality treatment of extremity soft tissue sarcomas

Various aspects of epilepsy, including its evolution, were studied in 78 children with mental retardation in a prospective 5-year (1989-1994) follow-up study. Level of mental retardation was moderate or even more severe (IQ < 50) in 83% of children, and 56% suffered from significant cerebral palsy. Epilepsy remained uncontrolled in 28% of cases, 2-year remission was achieved by 26%, and mortality was 12% during the study period. Associated cerebral palsy was the most important single risk factor for severe epilepsy, and several handicaps seemed to have a strong multiplicative effect. Complexity of epilepsy in children with mental retardation was reflected by the evolutionary features described.     

Skeletal and soft tissue sarcomas. Treatment with adjuvant immunotherapy

Because there is evidence for an active immunologic response against sarcoma, a clinical trial of adjuvant immunotherapy using bacillus Calmette-Guérin (BCG) and tumor cell vaccine was begun. Eleven of 18 patients with localized soft tissue sarcoma who received immunotherapy are free of disease, compared to only 5 of 15 treated by operation alone who are free of disease. Furthermore, immunotherapy also prolonged the median disease-free interval from 7.3 months to 15 months in the patients who experienced recurrence of their disease.     

Surgical aspects in the multidisciplinary treatment of soft tissue sarcomas

Sarcomas are rare malignant tumors with a large variety of histologic subtypes. The surgical approach depends more on the histologic grade, the size and the site of the tumor. Radiologic diagnosis relies predominantly on MR-imaging. Discernible improvements have taken place in soft tissue sarcoma patient survivorship and quality of life over the past 20 years, with overall 5-year survival currently at approximately 50-80%. The place of surgery in the treatment of soft-tissue sarcoma is defined in the light of a review of the recent literature. Radical surgical resection is the mainstay of therapy. Local recurrence is the most common type of failure. Local recurrence is resectable and limb preservations possible in the majority of patients. Survival after treatment of local recurrence is determined mainly by the grade and secondarily by the size of the tumor. The essential risk factor for local recurrence is the quality of surgical resection, defined by the definitive resection margins. A lateral safety margin of 5 cm and of 2 cm to the depth should be respected. In sarcoma of the extremity the compartment is defined based on clinical, radiographic, histopathologic and operative findings. The use of muscle flaps to fill the surgical defects can improve the functional result and reduce the complication rate. Only about 5% of the patients need amputation. Evaluation of functional results must be based on objective criteria. In retroperitoneal sarcoma the significant factors for determining prognosis are grade and completeness of exzision. Multidisciplinary treatment according to common protocols is essential. Shifts in treatment have taken place over the past decade, from single-modality treatment involving radical surgery with compartment resection to sophisticated limb-salvage strategies combined with radiation therapy. In case of inadequate surgery e.g. in a large tumor with positive margins in high-grade soft tissue sarcomas the addition of radiotherapy can improve local control, but cannot ensure that obtained by adequate surgery. Patients with large (greater than 5 cm), high grade soft tissue sarcoma are at high risk for distant recurrence and disease-related mortality. Investigations of combined modality therapy with newer chemotherapy agents and dose intensification treatment strategies are warranted.     

Phase II study of rapid-scheduled etoposide in paediatric soft tissue sarcomas

Twenty three patients with paediatric soft tissue sarcomas who had relapsed or refractory disease were treated with a rapid schedule of intravenous etoposide (100 mg/m2 daily on three consecutive days, weekly over 3 weeks). The regimen was well tolerated with predictable myelotoxicity. In 19 patients with rhabdomyosarcoma, there was a response rate of 42%. This appears to be better than previously reported with conventional three weekly schedules. These data indicate that for rhabdomyosarcoma, as for some other tumours, a divided dose regimen may be the optimal schedule and is worthy of further evaluation.     

Contribution of the cyclin-dependent kinase inhibitor p27KIP1 to the confluence-dependent resistance of HT29 human colon carcinoma cells

We have previously shown that growth of HT29 human colorectal cancer cells at confluence increased their resistance to the cytotoxic agent cisplatin. This study further explores the mechanisms of this resistance phenotype. DNA platination induced by cisplatin exposure is slightly reduced by confluence. However, at an equivalent DNA platination level, non-confluent cells accumulate in the G2/M phase of the cell cycle, demonstrate aberrant mitotic figures and die by apoptosis, while confluent cells progress slowly through the cell cycle, do not reach mitosis and are more resistant to drug-induced cell death. At a molecular level, cisplatin enhances cyclin B and p34cdc2 levels and histone H1 kinase activity in non-confluent, but not in confluent, cells. Furthermore, when HT29 cells reach confluence, expression of the cyclin-dependent kinase inhibitor p27Kip1 increases and cells accumulate in the G0/G1 phase of the cell cycle. Transfection-mediated over-expression of p27Kip1 in non-confluent HT29 cells decreases the cytotoxic activity of cisplatin as well as its ability to trigger apoptosis. Non-confluent HT29 cells over-expressing p27Kip1 are also more resistant to doxorubicin, etoposide and 5-fluorouracil. Our results suggest that p27Kip1 contributes to the confluence-dependent resistance phenotype.