Aberrant Somatic Hypermutation in Primary Mediastinal Large B-Cell Lymphoma.

Abstract

Primary mediastinal large B-cell lymphoma (PMLBCL) is recognised as a subtype of diffuse large B-cell lymphoma (DLBCL) arising in the mediastinum. With respect to DLBCL, PMLBCL displays specific clinical, molecular and morphological features suggesting that PMLBCL may represent a distinct clinico-pathologic entity. Aberrant somatic hypermutation (SHM) of PIM-1, PAX-5, RhoH/TTF and c-MYC has been advocated as a molecular feature distinctive of DLBCL. To investigate wether the same mechanism is associated with PMLBCL, we performed mutational analysis of PIM-1, PAX-5, RhoH/TTF and c-MYC in a panel of 19 PMLBCL. For comparison, 19 DLBCL were also analysed. For each gene, a region previously shown to contain >90% of mutations was analysed by PCR amplification and DNA direct sequencing. Overall, the prevalence of mutated cases was similar among DLBCL and PMLBCL. Mutations targeting at least one of the 4 genes were found in 14/19 (73.6%) PMLBCL and 13/19 (68.4%) DLBCL, while mutations in more than one gene were found in 7/19 (36.8%) PMLBCL and 9/19 (47.3%) DLBCL. Among the four genes, the prevalence of mutation and the mutation frequency was superimposable between PMLBCL and DLBCL. In fact, PAX-5 was mutated in 9/19 (47.3%) PMLBCL with a mean mutation frequency of 0.20 x 10−2/bp and in 7/19 (36.8%) DLBCL with a mean mutation frequency of 0.18 x 10−2/bp; RhoH/TTF was mutated in 6/19 (31.5%) PMLBCL with a mean mutation frequency of 0.08 x 10−2/bp and in 8/19 (42.1%) DLBCL with a mean mutation frequency of 0.27 x 10−2/bp; PIM-1 was mutated in 3/19 (15.7%) PMLBCL with a mean mutation frequency of 0.09 x 10−2/bp and in 7/19 (36.8%) DLBCL with a mean mutation frequency of 0.11 x 10−2/bp; c-MYC was mutated in 6/19 (31.5%) PMLBCL with a mean mutation frequency of 0.23 x 10−2/bp and in 5/19 (26.3%) DLBCL with a mean mutation frequency of 0.11 x 10−2. The mutation pattern was also similar between PMLBCL and DLBCL and was consistent with the SHM process. A total of 74 mutational events were detected in PMLBCL. The majority of mutations were represented by single base-pair substitution (n=66), whereas only 8 deletions of a short DNA stretch were observed. Of the 66 single base-pair substitutions, 41 were transitions and 25 were transversions, with a transition/transversion ratio of 1.64 and a G+C/A+T ratio of 3.6. Eleven out of 66 (16.6%) single base-pair substitutions felt within RGYW/WRCY motifs. Among DLBCL a total of 87 mutational events were detected. Mutations were preferentially represented by single base-pair substitutions (n=81), whereas only 4 deletions and 2 insertions of a short DNA stretch were observed. Of the 81 single base-pair substitutions, 42 were transitions and 39 were transversions, with a transition/transversion ratio of 1.07 and a G+C/A+T ratio of 1.89. Twenty six out of 81 (32.1%) single base-pair substitutions felt within RGYW/WRCY motifs. The implication of our results are twofold. First, aberrant SHM is involved in the pathogenesis of PMLBCL. Second, our results indicate that aberrant SHM targets both PMLBCL and DLBCL with similar prevalence, distribution and mutation pattern. Since aberrant SHM has been advocated as a molecular marker of DLBCL, our results corroborate the notion that PMLBCL represent a subtype of DLBCL rather than a distinct clinico-pathologic entity.

Targeting Pim kinases in hematological cancers: molecular and clinical review

“…Pim-1 is one of the critically deregulated oncogenes in T-ALL. Similar to B-ALL, genetic aberrations in Pim-1 gene locus have been found in T-ALL and T-LBL patients, t(6;7)(p21;q34), producing, TCRβ-PIM1 (T-cell receptor beta locus/PIM1), whereby the TCRβ enhancer was found juxtaposed to the 5'UTR (untranslated region) of the Pim-1 gene [105][106][107][108]. Although this genetic translocation is rare in T-ALL patients, TCRβ-PIM1+ T-ALL patients and T-ALL subgroups (HOXA, TLX, and LYL1+ (Lymphoblastic leukemia derived sequence 1)) that have JAK/STAT activating abnormalities (JAK1, JAK2, JAK3, IL7R, STAT5A/B, PTPN2 (protein tyrosine phosphatase non-receptor type 2), and/or NUP214-ABL1 (Nucleoporin Nup214-ABL1)) all lead to very high levels of Pim-1 gene expression [105,108].…”

“…These encompass, putative driver missense mutations, and amplifications, splice, missense, in frame, and truncating mutations of unknown significance. Pim-1 is one of four proto-oncogenes involved in DLBCL, PMLBCL, and FL SHA [102,105,106]. The 5'UTR of Pim-1, along with Pax-5 (Paired Box 5), RhoH/TFF (Ras homolog family member H/Trefoil Factor), and c-Myc, undergoes SHA with mutations occurring within coding exons leading to changes in amino acids and possibly Pim-1 activity.…”

B-cell lymphoma is unclassifiable, with signs intermediate between diffuse large-cell B-cell lymphoma and Hodgkin lymphoma

“…Так, вследствие ингибирования FAS-опосредованного апоптоза или апоптоза, ассоциированного с экспрессией BCL-2, развивается резистентность опухолевых клеток к апоптозу за счет продуктов генов, контролирующих NFkB, воздействуя на сигнальный путь ТNF-α (фактор некроза опухоли) [16]. Мутация 9р24.1 (JAK2/PD -L1-L2) -в 55% случаев отмечается при НВКЛ; в 25% -при ЛХ и в 75%при ДВККЛ [14,17] К Л И Н И ч е с К И е Н А Б Л ю Д е Н И я встречается в 27% случаев; наличие данной реаранжировки -один из неблагоприятных факторов, влияющих на продолжительность жизни пациентов с НВКЛ; 8q24 (MYC) -в 25% случаев [14]. Трудности диагностики НВКЛ у детей обусловлены редкой встречаемостью, отсутствием специфических клинических симптомов и лабораторных показателей, гистологическим сходством с другими типами лимфом.…”

Primary Mediastinal Large B-Cell Lymphoma

“…JAK-STAT positively regulate the expression of PDL1 and PDL2. These studies could be considered as preclinical model for a targeted therapy of PMBCL demonstrating that the blockade of NFKB, and JAK-STAT pathway as well as PD/PDL1 antibody could be potential therapeutic strategies (Rossi et al, 2005;Steidl and Gascoyne, 2011).…”