ABSTRACT
In acute promyelocytic leukemia (APL) the retinoic acid receptor alpha (RARα) becomes an oncogene through the fusion with several partners, mostly with promyelocytic leukemia protein (PML), all of which have in common the presence of a self-association domain. The new fusion proteins, therefore, differently from the wild-type RARα, which forms only heterodimers with retinoic X receptor alpha, are also able to homo-oligomerize. The presence of such a domain has been suggested to be crucial for the leukemogenic potential of the chimeric proteins found in APL blasts. Whether or not any self-association domain is sufficient to bestow a leukemogenic activity on RARα is still under investigation. In this work, we address this question using two different X-RARα chimeras, where X represents the coiled-coil domain of PML (CC-RARα) or the oligomerization portion of the yeast transcription factor GCN4 (GCN4-RARα). We demonstrate that in vitro both proteins have transforming potential, and recapitulate the main PML-RARα biological properties, but CC-RARα is uniquely able to disrupt PML nuclear bodies. Indeed, in vivo only the CC-RARα chimera induces efficiently APL in a murine transplantation model. Thus, the PML CC domain represents the minimal structural determinant indispensable to transform RARα into an oncogenic protein.
Subject(s)
Cell Transformation, Neoplastic , Leukemia, Promyelocytic, Acute/genetics , Nuclear Proteins/genetics , Receptors, Retinoic Acid/genetics , Recombinant Fusion Proteins/physiology , Transcription Factors/genetics , Tumor Suppressor Proteins/genetics , Animals , Blotting, Western , Chromatography, Gel , Fluorescent Antibody Technique , Hematopoietic Stem Cells/metabolism , Immunophenotyping , Immunoprecipitation , Leukemia, Promyelocytic, Acute/metabolism , Leukemia, Promyelocytic, Acute/pathology , Mice , Promyelocytic Leukemia Protein , Protein Multimerization , RNA, Messenger/genetics , Retinoic Acid Receptor alpha , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
AIMS: Diffuse large B-cell lymphomas (DLBCL) can be divided into different subgroups (germinal center B-cell-like [GCB] and non-GCB) according to their gene expression profiles. Immunohistochemistry has been proposed as a surrogate for identifying these subgroups, but data about its efficacy in providing prognostic information are conflicting. METHODS AND RESULTS: This study retrospectively analyzed a series of 105 DLBCL, defined as GCB and non-GCB according to CD10, bcl-6, and MUM1 expression. All patients received a first-line anthracycline-based (CHOP-like) chemotherapy. A total of 50 patients (48%) were identified as GCB and 55 (52%) as non-GCB. The overall response rate was 89% (94/105), with 62 (59%) complete response. Disease progressions were equally distributed between the 2 subgroups and were not significantly different (P = .756) considering the primary site of involvement (nodal or extranodal). The median follow-up was 62 months (range 5-126 months). Overall survival at 5 years was not significantly different between the groups (P = .3468) and was 72.3% and 66.6% for GCB and non-GCB, respectively. CONCLUSION: The results do not support the prognostic value of GCB and non-GCB immunohistochemical categories in DLBCL of both nodal and extranodal origin. Furthermore, a limited number of antigens may be not sufficient to identify the same patterns defined by cDNA microarray. Prospective studies are warranted to address this issue.
