p53 alterations in sequential biopsies of Asian follicular lymphoma: a study of immunohistochemical staining pattern and gene mutations by PCR-SSCP in paraffin-embedded tissues

Gene Analysis of Epstein-Barr Virus-Associated Lymphomas in Hu-PBL/SCID Chimeras

Aims and background

The mechanisms of Epstein-Barr virus (EBV)-associated tumor development are incompletely understood. The aim of this study was to investigate the gene expression of EBV-associated lymphomas in hu-PBL/SCID mice.

Methods

Human peripheral blood lymphocytes (hu-PBL) from EBV-seropositive donors were transplanted into severe combined immunodeficiency (SCID) mice. In situ hybridization was used to detect EBV-encoded small RNA-1 (EBER1) in tumor tissues. Mutation of TP53 exons 5–8 in EBV-induced lymphomas was analyzed by PCR-SSCP. Immunohistochemical staining was used to examine EBV gene products and cellular oncoproteins.

Results

Twenty-one of 29 mice developed tumors. EBER1 was positive in the nuclei of almost all tumor cells. Immunohistochemistry showed positive staining of LMP1, EBNA2 and ZEBRA in a small number of tumor cells. Immunohistochemically detectable p53 protein expression was common (85.7%), but TP53 gene mutations were identified in only four cases (19.1%) of EBV-associated lymphomas. Positivity rates of C-myc, Bcl-2 and Bax expression were 100%, 95.2%, and 90.5%, respectively, in the 21 cases of EBV-associated lymphomas.

Conclusions

Our preliminary findings suggest that EBV-associated lymphomas in hu-PBL/SCID chimeras show EBV infection, expression of oncogenic viral genes, and overexpression of cellular oncogenes. TP53 gene mutations are rare but p53 protein is commonly expressed in EBV-associated lymphomas.

The role of cell cycle regulatory proteins in the pathogenesis of melanoma

The transformation of melanocytes to melanoma cells is characterised by abnormal proliferation resulting from alterations in cell cycle regulatory mechanisms. This occurs through alterations in the two major cell cycle regulatory pathways, the retinoblastoma (Rb) and p53 tumour suppressor pathways. This review summarises the current knowledge of alterations in these two pathways at G1/S transition and specifically the role of the key cell cycle regulatory proteins pRb, p16INK4a (p16), cyclin D1, p27Kip1 (p27), p53 and p21Waf1/Cip1 (p21) in the pathogenesis of melanoma. It also considers their prognostic significance. Current data indicate that alterations of cyclin kinase inhibitor (cdki) levels are implicated in the pathogenesis of melanoma and may be useful prognostic markers. However, large validation studies linked to comprehensive clinical follow up data are necessary to clarify the prognostic significance of cell cycle regulatory proteins in individual patients.

Mutations in Exons 6 and 7 of TP53 Gene Correlate Positively with Serum Tumor Necrosis Factor Alpha Independent of Microsatellite Instability in BAT26 Gene in Egyptian Patients with Endometrial Carcinoma

Abnormalities in the TP53 gene are the most frequent genetic alterations in human cancers. The role and mechanism of TP53 mutations have been well studied in many types of human cancer. Similarly, the presence of microsatellite instability (MSI) in the DNA mismatch repair system (hMSH2) may provide evidence of faulty DNA mismatch repair. One of the most important locations of MSI is the BAT26 gene. In addition, deranged serum cytokines, especially elevated levels of the tumor necrosis factor (TNF) alpha, have been found in many gynecological conditions.

Aims

The current study aimed at evaluating mutations in exons 6 and 7 of TP53 and the presence of microsatellite instability in BAT26 of the hMSH2 system in Egyptian patients with endometrial carcinoma. The study also evaluated whether there was a correlation between any of these genetic mutations/instability and the tissue expression of estrogen and progesterone receptors and the serum TNF-alpha level.

Patients and methods

The current study included 2 groups: a control group comprising 20 healthy women aged 52.21 ± 5.80 years attending the clinic for routine checkups and 40 patients with endometrial cancer aged 55.30 ± 6.21 years. Mutations in TP53 and BAT26 were evaluated using polymerase chain reaction–single-strand conformational polymorphism (PCR-SSCP) and automated sequencing while serum TNF-alpha was measured using an ELISA technique. Estrogen and progesterone receptor expression in biopsy tissue was evaluated using immunohistochemical staining.

Results

Seven of the 40 patients (17.5%) were positive for TP53 gene alterations in exon 6, while 9 patients (22.5%) were positive for TP53 alterations in exon 7. Cases positive for TP53 mutations had higher tumor stages. Ten patients (25%) showed MSI in BAT26. Nearly all patients with mutations in BAT26 had a strong family history for endometrial cancer (χ2=13.33, p<0.05). There was no positive correlation between the presence of MSI in the BAT26 gene and mutations in the TP53 gene or high serum TNF-alpha levels. Cases positive for TP53 mutations had a significantly higher level of TNF-alpha than cases negative for TP53 mutations (p<0.05). Cases showing mutations in exon 6 or 7 of TP53 showed a significantly higher intensity of immunohistochemical staining for estrogen and progesterone receptor expression in biopsy tissue than cases negative for mutations. (χ2=8.11, p<0.05).

Conclusion

Our results suggest that the development of endometrial carcinoma is probably mediated through a multi-step carcinogenesis pathway and mutation of TP53 does not necessarily result from the presence of microsatellite instability in BAT26. The high serum TNF-alpha levels detected in our patients may represent an immunological antitumor response that was particularly evident in cases positive for TP53 mutations.