Interphase cytogenetic analysis of non-Hodgkin's lymphoma

Elevated levels of MDM-2 and p53 expression are associated with high grade non-Hodgkin's lymphomas

The role of p53 in the evolution of non-Hodgkin's lymphomas (NHL) is unclear. Mutations of the p53 gene appear to be relatively uncommon but stabilized p53 protein, as detected by immunohistochemistry, has indicated a more frequent involvement of p53. As dysfunction of p53 protein has also been suggested to occur after overexpression of the mdm-2 protein, we have therefore investigated a series of non-malignant hyperplastic reactive lymphoid tissues and NHL to examine whether the levels of expression of MDM-2 correlated to positivity of p53 protein staining. Northern blot analysis of MDM-2 expression was compared to glucose-6-phosphate dehydrogenase (G6PD) expression by densitometry to quantify the relative levels of MDM-2 expression. Consistent low levels of MDM-2 expression were observed in non-malignant lymphoid tissue and in low grade NHL, however, 13/15 high grade NHL exhibited a 2-15-fold increase in MDM-2 expression. Interestingly similar elevations in p53 mRNA expression were also observed in 6/15 high grade NHL. Positive staining of the p53 protein did not, however, correlate with elevated mRNA levels of either MDM-2 or p53. The significance of these observations is discussed.

Investigation of BCL-2 gene rearrangements in a United Kingdom series of low and high grade non-Hodgkin's lymphomas

Rearrangements of the BCL-2 gene are thought to be the most frequent genetic changes that occur in non-Hodgkin's lymphomas (NHL), and are particularly associated with follicular low grade disease. Wide variations in the frequency of these rearrangements have, however, been reported in studies of NHL series from different parts of the world. We were therefore interested to determine the frequency of BCL-2 gene rearrangements in the different grades of NHL from a U.K. series. We have done this by using a combination of Southern blot hybridization and polymerase chain reaction (PCR) analysis. The frequencies of rearrangements in our series were 9/20 (45%) in low grade follicular NHL, 1/8 (12.5%) in low grade lymphocytic and 5/19 (26%) in high grade NHL. However, estimation of the high grade value was complicated by the fact that a number of the high grade samples in our series were from patients who had transformed from low grade follicular disease. If the patients were ranked on the basis of whether they had a history of low grade follicular disease then the frequency of BCL-2 rearrangement remained the same 13/29 (45%), but was only 1/10 (10%) in high grade NHL with no history of follicular disease. The former figure was intermediate between those reported for the USA and Japan series, but the latter high grade figure was the lowest reported from any series. The significance of BCL-2 rearrangements in the evolution of both low and high grade NHL is discussed.