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Biomedical subjects

Kenan Onel

Publications and source records attributed to Kenan Onel.

6 recordsLinked to original sources
PubMed2005

The TP53 mutational spectrum and frequency of CHEK2*1100delC in Li-Fraumeni-like kindreds.

Li-Fraumeni syndrome (LFS) is a dominantly inherited cancer predisposition syndrome characterized by a wide spectrum of neoplasms occurring at young age. Germline mutations in the TP53 tumor suppressor gene have been identified in approximately 71 of LFS patients and 22 of Li-Fraumeni-like (LFL) patients. Mutations within the cell cycle checkpoint gene CHEK2 have also been reported in some patients with LFS, LFL, and phenotypically suggestive of LFS (PS-LFS) not carrying a TP53 mutation. In this study, we show that 7 of the 23 patients with LFS/LFL tested positive for deleterious mutations in p53. Fifteen of the remaining sixteen were not found to carry the CHEK2* 1100delCmutation. These results indicate that CHEK2*1100delC is not a common cause of LFS, LFL, or PS-LFS in North American kindreds not carrying a TP53 mutation. Of note, two patients were found to carry p53* R72P, which is of unknown clinical significance. Lack of segregation of this allele in one of these kindreds provides strong evidence that the R72P allele is not disease-causing. While mutations in p53 account for a proportion of patients with LFS/LFL, future studies are needed to determine if other genes are responsible for LFS/LFL families not carrying germline p53 mutations.

Adolescent↗
PubMed2004

A single nucleotide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans.

The tumor suppressor p53 gene is mutated in minimally half of all cancers. It is therefore reasonable to assume that naturally occurring polymorphic genetic variants in the p53 stress response pathway might determine an individual's susceptibility to cancer. A central node in the p53 pathway is the MDM2 protein, a direct negative regulator of p53. In this report, a single nucleotide polymorphism (SNP309) is found in the MDM2 promoter and is shown to increase the affinity of the transcriptional activator Sp1, resulting in higher levels of MDM2 RNA and protein and the subsequent attenuation of the p53 pathway. In humans, SNP309 is shown to associate with accelerated tumor formation in both hereditary and sporadic cancers. A model is proposed whereby SNP309 serves as a rate-limiting event in carcinogenesis.

Adult↗
PubMed2004

The genetics of familial lymphomas.

Whereas familial clustering of malignant lymphoma is well documented, the molecular changes underlying familial lymphoma syndromes remain unclear. An understanding of the hereditary basis of lymphoma may lead to the identification of new molecular markers for disease or novel therapeutic targets. This paper reviews the genetics of familial lymphoma, focusing on germline susceptibilities to lymphoma as well as germline susceptibilities to environmental exposures that have been linked to lymphoma.

Chromosome Aberrations↗
PubMed2004

MDM2 and prognosis.

The cellular stress response pathway regulated by the p53 tumor suppressor is critical to the maintenance of genomic integrity and to the prevention of oncogenic transformation. Intracellular levels of p53 are tightly regulated by an autoregulatory feedback loop comprised of p53 and MDM2. It might be predicted that disruption of this loop, either through p53 mutation or overexpression of MDM2, would be a negative prognostic marker for cancer development, likelihood of relapse, or response to therapy. In fact, although MDM2 overexpression is common in cancer, it can be both a positive and a negative predictor of outcome in different tumors, and its significance as a biomarker remains controversial. Data from a number of different tumor types are reviewed for the predictive significance of MDM2 expression, along with evidence for different mechanisms of MDM2 overexpression in these different tumors. In light of the biological complexities underlying the p53-MDM2 loop, it is, perhaps, not surprising that no simple paradigm exists that is generally applicable. Much work remains to be done to elucidate the basic mechanisms underlying the physical interactions between the two proteins, the role of protein modifications in altering those interactions, and also the genetic and transcriptional deregulations by which protein levels are altered in human cancers. Only in this way will truly biologically relevant predictive factors emerge.

Animals↗
PubMed2003

Differential recruitment of caspase 8 to cFlip confers sensitivity or resistance to Fas-mediated apoptosis in a subset of familial lymphoma patients.

Resistance to Fas-mediated apoptosis (FMA) has been implicated in the pathogenesis of hematologic malignancies. Recently, a collaborative study showed that germline Fas mutations represent a genetic risk factor for the development of Hodgkin's and non-Hodgkin lymphoma. Here, we report that transformed B cell lines from familial lymphoma patients show a range of sensitivity to Fas-mediated apoptosis with lymphocytes from two patients with a marked resistance to Fas-, but not p53-mediated cell death. Fas resistance in these cells was associated with reduced recruitment of the initiator caspase 8 compared to cFlip, an inhibitor of apoptosis, to the death-inducing signaling complex (DISC). A decreased ratio of caspase 8 to cFlip in total cell extracts as well as in the DISC was associated with a profound disturbance of the Fas signaling cascade. We propose here that the relative reduction in caspase 8 to cFlip in the Fas DISC confers a survival advantage to lymphocytes and predisposes to the development of malignancy in some familial lymphoma patients.

Aged↗