Translocation t(14;18) and gain of chromosome 18/BCL2: effects on BCL2 expression and apoptosis in B-cell non-Hodgkin's lymphomas

Abstract

Gain of chromosome 18q and translocation t(14;18) are] frequently found in B-cell non-Hodgkin's lymphomas (B-NHL). Increased BCL2 transcription and BCL2 protein expression have been suggested to be the result of the gain. We utilized FISH, PCR and array CGH to study BCL2 and chromosome 18 copy number changes and rearrangements in 93 cases of B-NHL. BCL2 protein was expressed in 475% of the tumor cells in 92% of the cases by immunohistochemistry. Gain of BCL2 was associated with a 25% increase in BCL2 expression levels (immunoblotting), whereas t(14;18) resulted in a 55% increase in BCL2 levels compared to cases without BCL2 alterations. The tumor cell (spontaneous) apoptotic fractions were similar for the cases with different BCL2 genotypes. However, the normal cell apoptotic fractions were higher for the tumors with t(14;18) compared to the tumors without BCL2 alterations, while the tumors with gain of BCL2 only showed intermediate levels.Low-level gains of parts of chromosome 18 were found in 14 of the 38 B-NHL cases with t(14;18), with a consensus region 18pter-q21.33 that did not include the BCL2 gene. The 11 cases with 18q gain only showed a consensus region encompassing 18q21.2-18q21.32 and 18q21.33, which contain PMAIP1/MALT1 and BCL2, respectively.

Gain of chromosome 6p is an infrequent cause of increased PIM1 expression in B-cell non-Hodgkin's lymphomas

“…Conversely, the C-terminal PEST domain is an important negative regulatory site required for ICN degradation, and loss of this region also leads to increased activity in the Notch-sensitive reporter assay, probably through stabilization of ICN. 3 All PEST domain mutations detected in our patients would lead to a similarly truncated protein. The probable functional consequence of the mutations identified in our study is supported by the loss of these mutations at remission and reappearance at relapse, which provides conclusive evidence that they are acquired and are specifically associated with the leukemic clone.…”

“…Functional analysis using a Notch-sensitive luciferase reporter assay has shown that leucine to proline point mutations in the HD domain lead to increased activity. 3 At least 10 of the 13 different HD domain mutations detected in our cohort are likely to result in an altered conformation, either through insertion of a proline residue, or loss or gain of amino acids. Conversely, the C-terminal PEST domain is an important negative regulatory site required for ICN degradation, and loss of this region also leads to increased activity in the Notch-sensitive reporter assay, probably through stabilization of ICN.…”

“…2 The general procedures of DNA isolation, CGH hybridizations and gene copy number analysis by FISH has been described earlier. 3 A local DNA gain mapping to region 6p21 was identified by conventional CGH analysis (Figure 1a). To identify genes in the amplified region, we performed array CGH analysis using a BAC-array with an average spacing of 1 Mbp between the probes (Figure 1b).…”

“…7 Furthermore, g-secretase inhibitors (GSI) have been shown to induce cell cycle arrest in vitro in T-ALL cell lines harboring Notch-1 mutations 3 and therefore may offer a rational molecularly targeted approach for these patients who, in the older age group, have a poor outcome with current therapy. The experience gained from clinical trials using GSIs for Alzheimer's disease, where they inhibit the production of beta amyloid peptide from amyloid precursor protein, should expedite trials of these agents in T-ALL.…”

“…Of the 18 different mutations identified, only four have been previously described in the pediatric cohort or T-ALL cell lines. 3 The HD domain is responsible for stable association of Notch-1 subunits 6 and structural integrity in this region is required to prevent exposure of the site to unregulated proteolytic cleavage. Functional analysis using a Notch-sensitive luciferase reporter assay has shown that leucine to proline point mutations in the HD domain lead to increased activity.…”