p53 intronic point mutation, aberrant splicing and telomeric associations in a case of B-chronic lymphocytic leukaemia

Overexpression and Mutation of p53 Exons 4-8 in Canine Intestinal Adenocarcinoma

p53 is mutated and overexpressed during malignant transformation, including in human colorectal cancer. This study investigated the overexpression of p53 protein and mutations in the p53 gene in canine intestinal neoplasia (CIN). Immunohistochemical analysis of p53 was carried out in formalin-fixed and paraffin wax-embedded (FFPE) sections of intestinal tissues from 35 dogs with CIN by the standard peroxidase-anti-peroxidase method. Expression of p53 protein in malignant (adenocarcinoma, n = 20) and benign (adenoma and polyp, n = 8) CINs was compared with tissue from negative controls (samples with no proliferation, n = 7). DNA was extracted from FFPE tissue from one control and 13 cases with overexpression of p53, and exons 4-8 were sequenced. p53 expression was higher in malignant than in benign tissues (P = 0.001). Sequencing was successfully performed in nine cases and mutations were confirmed in three of these cases. One non-sense mutation, one missense mutation and one germline mutation were confirmed for the three cases. This study suggests that p53 overexpression can be a prognostic factor for CIN; however, p53 overexpression in CIN may occur through a mechanism distinct from mutations within the p53 exon 4-8 region.

Chronic lymphocytic leukemia with isochromosome 17q: An aggressive subgroup associated with TP53 mutations and complex karyotypes

Although i(17q) [i(17q)] is frequently detected in hematological malignancies, few studies have assessed its clinical role in chronic lymphocytic leukemia (CLL). We recruited a cohort of 22 CLL patients with i(17q) and described their biological characteristics, mutational status of the genes TP53 and IGHV and genomic complexity. Furthermore, we analyzed the impact of the type of cytogenetic anomaly bearing the TP53 defect on the outcome of CLL patients and compared the progression-free survival (PFS) and overall survival (OS) of i(17q) cases with those of a group of 38 CLL patients harboring other 17p aberrations. We detected IGHV somatic hypermutation in all assessed patients, and TP53 mutations were observed in 71.4% of the cases. Patients with i(17q) were more commonly associated with complex karyotypes (CK) and tended to have a poorer OS than patients with other anomalies affecting 17p13 (median OS, 44 vs 120 months, P = 0.084). Regarding chromosomal alterations, significant differences in the median OS were found among groups (P = 0.044). In conclusion, our findings provide new insights regarding i(17q) in CLL and show a subgroup with adverse prognostic features.

Immunohistochemical correlates of TP53 somatic mutations in cancer

Despite controversy on the correlation between p53 accumulation and TP53 mutational status, immunohistochemical (IHC) detection of overexpressed protein has long been used as a surrogate method for mutation analysis. The aim of our study was to characterise the IHC expression features of TP53 somatic mutations and define their occurrence in human cancers. A large-scale database analysis was conducted in the IARC TP53 Database (R17); 7878 mutations with IHC features were retrieved representing 60 distinct tumour sites. The majority of the alterations were immunopositive (p <0.001). Sex was known for 4897 mutations showing a female dominance (57.2%) and females carrying negative mutations were significantly younger. TP53 mutations were divided into three IHC groups according to mutation frequency and IHC positivity. Each group had female dominance. Among the IHC groups, significant correlations were observed with age at diagnosis in breast, bladder, liver, haematopoietic system and head & neck cancers. An increased likelihood of false negative IHC associated with rare nonsense mutations was observed in certain tumour sites. Our study demonstrates that p53 immunopositivity largely correlates with TP53 mutational status but expression is absent in certain mutation types.Besides, describing the complex IHC expression of TP53 somatic mutations, our results reveal some caveats for the diagnostic practice.

Mutation of p53 Gene and Its Correlation with the Clinical Outcome in Dogs with Lymphoma

Background

p53 plays a key role in the apoptotic event induced by chemotherapeutic agents. Mutation of p53 gene has been observed in various spontaneous tumors in humans and is associated with a poor prognosis. p53 abnormalities have been evaluated in several tumors in dogs; however, the association of p53 gene mutation with clinical outcome in dogs with lymphoma has not been documented.

Hypothesis/Objectives

The aim of this study was to examine p53 mutation in canine lymphoma cells and its association with the clinical outcome.

Animals

Forty‐three dogs with previously untreated high‐grade lymphoma referred to the University of Tokyo were included in this study.

Methods

Prospective cohort study. We examined p53 gene (exon 4–8) mutation in the tumor tissues from 43 dogs with lymphoma using PCR‐SSCP (polymerase chain reaction – single‐strand conformational polymorphism) analysis, followed by nucleotide sequencing of the abnormal bands.

Results

Of the 43 dogs, 7 dogs (16%) had p53 mutation, whereas 36 dogs (84%) were devoid of p53 mutation. Overall response rate after remission induction was significantly lower (33% versus 88%, P = .002) in dogs with lymphomas having p53 mutation than those with lymphomas devoid of p53 mutation. Overall survival time was significantly shorter (67 days versus 264 days, P = .004) in dogs with lymphoma with p53 mutation than those with lymphoma retaining wild‐type p53.

Conclusion and Clinical Importance

Mutations of p53 gene were detected in a proportion of canine lymphoma cells from untreated dogs and can be associated with a poor prognosis.

New molecular markers in resistant B-CLL

B-chronic lymphocytic leukemia (B-CLL) is characterized by a highly variable clinical course which has long remained a stumbling block for clinicians. This variability appears to arise from complex molecular alterations identified in malignant cells from patient subsets. Recent studies have focused in particular on identifying new molecular markers to help predict the most effective and adapted treatments. In addition to the mutation status of immunoglobulin variable heavy-chain region (IgVH) genes, which is a well-established predictive factor in B-CLL, these new markers include defects of cell factors involved in the maintenance of genome stability, such as telomere function, DNA repair, ATM and p53. Other predictive factors, such as tyrosine kinase Zap-70 and soluble factors found in patient sera, may be associated with B-cell receptor signal transduction. Interestingly, an alteration of these factors fits closely, though not strikingly, with the absence of somatic mutations in IgVH genes, suggesting that the latter may be due either to epigenetic events leading to an unstable genome or to an inherited defect in the immune response of malignant B-cells. Recent lessons from Zap-70 expression/phosphorylation suggest that some of these markers may reflect the defective pathways in B-CLL cells rather than being markers of cell malignancy per se. Furthermore, specific subsets of markers are found in patient cells resistant to treatment. Current studies on gene expression profiling and proteomic analyses should soon lead to a better understanding of how these pathways are affected, especially in multi-drug resistant B-CLL.

Inherited and acquired variations in the hyaluronan synthase 1 (HAS1) gene may contribute to disease progression in multiple myeloma and Waldenstrom macroglobulinemia

To characterize genetic contributions toward aberrant splicing of the hyaluronan synthase 1 (HAS1) gene in multiple myeloma (MM) and Waldenstrom macroglobulinemia (WM), we sequenced 3616 bp in HAS1 exons and introns involved in aberrant splicing, from 17 patients. We identified a total of 197 HAS1 genetic variations (GVs), a range of 3 to 24 GVs/patient, including 87 somatic GVs acquired in splicing regions of HAS1. Nearly all newly identified inherited and somatic GVs in MM and/or WM were absent from B chronic lymphocytic leukemia, nonmalignant disease, and healthy donors. Somatic HAS1 GVs recurred in all hematopoietic cells tested, including normal CD34(+) hematopoietic progenitor cells and T cells, or as tumor-specific GVs restricted to malignant B and plasma cells. An in vitro splicing assay confirmed that HAS1 GVs direct aberrant HAS1 intronic splicing. Recurrent somatic GVs may be enriched by strong mutational selection leading to MM and/or WM.

Aberrant 3' splice sites in human disease genes: mutation pattern, nucleotide structure and comparison of computational tools that predict their utilization

The frequency distribution of mutation-induced aberrant 3' splice sites (3'ss) in exons and introns is more complex than for 5' splice sites, largely owing to sequence constraints upstream of intron/exon boundaries. As a result, prediction of their localization remains a challenging task. Here, nucleotide sequences of previously reported 218 aberrant 3'ss activated by disease-causing mutations in 131 human genes were compared with their authentic counterparts using currently available splice site prediction tools. Each tested algorithm distinguished authentic 3'ss from cryptic sites more effectively than from de novo sites. The best discrimination between aberrant and authentic 3'ss was achieved by the maximum entropy model. Almost one half of aberrant 3'ss was activated by AG-creating mutations and approximately 95% of the newly created AGs were selected in vivo. The overall nucleotide structure upstream of aberrant 3'ss was characterized by higher purine content than for authentic sites, particularly in position -3, that may be compensated by more stringent requirements for positive and negative nucleotide signatures centred around position -11. A newly developed online database of aberrant 3'ss will facilitate identification of splicing mutations in a gene or phenotype of interest and future optimization of splice site prediction tools.

Inactivating I kappa B epsilon mutations in Hodgkin/Reed-Sternberg cells

The pathogenesis of Hodgkin lymphoma (HL) is still unclear. Previous investigations have demonstrated constitutive nuclear activity of the transcription factor NF kappa B (NF-kappaB) in Hodgkin/Reed-Sternberg (HRS) cells as an important prerequisite in protecting these cells from apoptosis. As a molecular mechanism leading to constitutive NF-kappaB activity in HRS cells, mutations of the NF-kappaB inhibitor I kappa B alpha (IkappaBalpha) have recently been identified in classical (c) HL-derived cell lines in a patient with cHL. In the present study, the NF-kappaB inhibitor I kappa B epsilon (IkappaBepsilon) has been analysed for somatic mutations in the same group of six patients already studied for IkappaBalpha mutations, as well as in cHL-derived cell lines. In one cHL-derived cell line (L428), a hemizygous frame-shift mutation generating a pre-terminal stop codon resulting in a severely truncated protein was found. Moreover, in the HRS cells of one patient, a hemizygous mutation affecting the 5'-splicing site of intron 1 of the IkappaBepsilon gene was found. These results, in combination with recently described IkappaBalpha mutations, indicate that defective NF-kappaB inhibitors appear more frequent than previously thought and might explain the constitutive nuclear activity of NF-kappaB in a significant proportion of cHL cases.