Proteins encoded by genes involved in chromosomal alterations in lymphoma and leukemia: clinical value of their detection by immunocytochemistry

Abstract

IntroductionTranslocations, deletions, and other nonrandom chromosomal abnormalities 1,2 play a central role in the pathogenesis of many human hematologic malignant diseases. A growing number of studies are revealing the ways in which these chromosomal alterations affect specific genes, such as those encoding nuclear transcription factors. However, any gene implicated in the neoplastic process can act only through the protein it encodes. Many of the consequences of chromosomal changes with respect to abnormal protein expression have been inferred indirectly by analysis of messenger RNA (mRNA) transcription, but it is clear that protein and mRNA levels do not always correlate. For example, germinalcenter B cells appear to contain BCL-2 message but little protein, 3,4 and the same is true for TAL-1 in erythroid cells. 5 Many examples of the opposite combination (high protein and little or no message) also exist, such as BCL-2 in mature lymphocytes 6,7 and elastase in mature myeloid cells. 8 Antibody-based detection of the protein is therefore required, but this frequently cannot be done because of a lack of suitable reagents. Consequently, we are often ignorant not only about patterns of expression of oncogenic proteins in hematologic neoplasms but also about possible abnormalities in the distribution and subcellular localization of these proteins.Most of the currently recognized genetic alterations in human leukemias and lymphomas result in either activation of a quiescent gene or creation of a hybrid gene encoding a chimeric protein. Table 1 summarizes the genetic abnormalities that have been studied using antibodies specific for the protein products of genes involved in such rearrangements. We here review the immunocytochemical studies that have been done with these antibodies and assess, for each protein, whether abnormalities demonstrable by immunocytochemistry are of clinical value in determining diagnosis or predicting prognosis. Immunocytochemical findings that are of value are discussed below, whereas those for which no clear clinical applications have been observed are described briefly in Table 2. Genes activated by chromosomal changesThe CCND1 (BCL-1) gene and its protein product (cyclin D1) CCND1 (BCL-1) gene. The (11;14)(q13;q32) translocation, 9 an anomaly often found in mantle cell (centrocytic) lymphoma 10,11 and occasionally in other B-cell neoplasms, notably myeloma, 12,13 From For personal use only. on May 12, 2018. by guest www.bloodjournal.org From juxtaposes the CCND1 (BCL-1) locus encoding cyclin D1 on chromosome 11 to an immunoglobulin-enhancer sequence on chromosome 14. 9 The CCND1 gene is transcriptionally silent in normal lymphohemopoietic tissues 14,15 ; thus, expression of the protein may promote neoplastic cell proliferation by perpetuating the transition from G 1 to S. 16 Antibodies to cyclin D1. Several antibodies recognizing cyclin D1 have been described (Table 3), [14][15][16][17][18] but hematopathologists know that immunocytochemical detection of cyclin D1 in routinely processe...

Aberrant subcellular expression of nucleophosmin and NPM-MLF1 fusion protein in acute myeloid leukaemia carrying t(3;5): A comparison with NPMc+ AML

“…1 Although NPM is known to shuttle back and forth between the nucleus and the cytoplasm, 2 only a minimum amount of the protein is present at any time in the cytoplasm; this explains why with immunohistochemistry NPM is only detectable at the nucleolar level. 3 We previously showed that NPM is aberrantly expressed in the cytoplasm of anaplastic large cell lymphoma cells carrying t(2;5), due to the presence of the NPM-ALK fusion protein. 3 Ectopic NPM expression parallels that of ALK protein and serves as a highly specific diagnostic test on routine biopsies.…”

“…3 We previously showed that NPM is aberrantly expressed in the cytoplasm of anaplastic large cell lymphoma cells carrying t(2;5), due to the presence of the NPM-ALK fusion protein. 3 Ectopic NPM expression parallels that of ALK protein and serves as a highly specific diagnostic test on routine biopsies. 3 The t(3;5)(q25;q35) is a rare chromosomal translocation which is detected in myelodysplastic syndromes and acute myeloid leukaemia (AML), 4 more frequently of FAB-M6 type.…”

Altered nucleophosmin transport in acute myeloid leukaemia with mutated NPM1: molecular basis and clinical implications

“…46 Nevertheless, the view that the NPM1 moiety of the chimeric protein only provides a dimerization substrate for the C-terminal onco-protein has recently been challenged by in vivo evidence that NPM1 is an haploinsufficient tumour suppressor gene. 55 Therefore, its heterozygous loss could also contribute to the pathogenesis of the disease.…”

“…Because of its ALK moiety, at least a proportion of the NPM1-ALK protein anchors to ALCL cell cytoplasm. 46 This accounts for the aberrant cytoplasmic expression of nucleophosmin that is revealed with antibodies against the NPM1 N-terminus (which is retained in the fusion protein). 46,49 In contrast, NPM1wt that can be detected with an antibody against NPM1 C-terminus (that is not retained in NPM1-ALK), maintains its expected nucleolar expression in ALCL with t(2;5), 49 suggesting that localization is not perturbed by the NPM1-ALK fusion product.…”

“…The usual positivity of NPM1wt in paraffin-embedded samples is 'nucleus-restricted, diffuse' rather than nucleolar, 26,45 reflecting the limits of immunohistochemical staining of paraffin sections in detecting subnuclear structures, such as nucleoli or nuclear bodies. 46 In normal human tissues, immunohistochemistry also identifies a small percentage of cells that express nucleophosmin in cytoplasm in the absence of NPM1 mutations. These represent cells in mitosis as well as post-mitotic and apoptotic elements in which NPM1wt localizes in the cytoplasm because of loss of nuclear membrane (mitosis) or diffusion of the protein from nucleus to cytoplasm (apoptosis) (Falini B, unpublished observation).…”