Mechanisms of Regulation of the Human c-myb Proto-oncogene During Myelomonocytic Differentiation

Control of hematopoiesis is a complex set of events that is currently being dissected at the molecular level. To determine factors that may be crucial for commitment to terminal differentiation of myelomonocytic cells, a mutant of the HL-60 cell line was characterized at the cellular and molecular level. This clone, termed DMSOr, was shown to differentiate in a similar fashion as parental HL-60 in response to 1.3% DMSO at the morphologic and functional level. The anti-proliferative aspects of differentiation were also present in DMSOr as evidenced by decreased 3H-thymidine incorporation and an increased percentage of cells in the G0/G1 phase of the cell cycle. All of these phenotypic changes induced in DMSOr would revert if the DMSO was removed at any point during the differentiation process, thus DMSOr, despite its ability to functional differentiate, could not commit to terminal differentiation. Associated with the altered phenotype of DMSOr was the altered expression of the proto-oncogene c-myb. Expression of cmyb remained detectable at 144 hrs of DMSO treatment in DMSOr but not HL-60. Similar findings were shown for the cell cycle other related genes. This altered gene expression did not extend to the c-myb related gene B-myb. The possibility that altered transcriptional regulation of c-myb was eliminated by nuclear run-on analysis and by the fact that a splice variant of c-myb with an altered 3\u27 untranslated region showed no altered regulation. Thus the genetic defect in DMSOr may be in a global control factor for cell cycle related genes such as c-myb. This factor may regulate these genes at the post-transcriptional level. To determine the mechanisms of regulation of c-myb during hematopoietic cell differentiation, transcriptional and posttranscriptional studies of c-myb following treatment of HL-60 cells with various differentiation inducers were undertaken. Retinoic acid and vitamin D3 regulated c-myb at the transcriptional level via an attenuator, while DMSO and phorbol dibutyrate activated multiple mechanisms of regulation. These included attenuation and a post-transcriptional regulation that was dependent on continuous transcription, but not translation in the case of DMSO. Phorbol ester regulation of c-myb occurred at the level of an attenuator and possibly a promoter at the transcriptional level. In addition there was post-transcriptional control of c-myb by phorbol dibutyrate that differed from the regulation by DMSO through the lack of transcriptional dependency. Thus c-myb is regulated at the transcriptional and the post-transcriptional level in an agent specific fashion during HL-60 differentiation. A 2.4 kb message is present in the Northern blots probed for c-myb expression. This lower molecular weight message is regulated in an abberrant fashion compared to normal message during HL-60 differentiation. Probing of blots with different regions of a full length c-myb eDNA and primer extension analysis suggest that the 2.4 kb message may start in the exon of the c-myb locus

Cell of Origin and Genetic Alterations in the Pathogenesis of Multiple Myeloma

B cell activation and differentiation yields plasma cells with high affinity antibodies to a given antigen in a time-frame that allows for host protection. Although the end product is most commonly humoral immunity, the rapid proliferation and somatic mutation of the B cell receptor also results in oncogenic mutations that cause B cell malignancies including plasma cell neoplasms such as multiple myeloma. Myeloma is the second most common hematological malignancy and results in over 100,000 deaths per year worldwide. The genetic alterations that occur in the germinal center, however, are not sufficient to cause myeloma, but rather impart cell proliferation potential on plasma cells, which are normally non-dividing. This pre-malignant state, referred to as monoclonal gammopathy of undetermined significance or MGUS, provides the opportunity for further genetic and epigenetic alterations eventually resulting in a progressive disease that becomes symptomatic. In this review, we will provide a brief history of clonal gammopathies and detail how some of the key discoveries were interwoven with the study of plasma cells. We will also review the genetic and epigenetic alterations discovered over the past 25 years, how these are instrumental to myeloma pathogenesis, and what these events teach us about myeloma and plasma cell biology. These data will be placed in the context of normal B cell development and differentiation and we will discuss how understanding the biology of plasma cells can lead to more effective therapies targeting multiple myeloma

A MCP1 fusokine with CCR2-specific tumoricidal activity

<p>Abstract</p> <p>Background</p> <p>The CCL2 chemokine is involved in promoting cancer angiogenesis, proliferation and metastasis by malignancies that express CCR2 receptor. Thus the CCL2/CCR2 axis is an attractive molecular target for anticancer drug development.</p> <p>Methods</p> <p>We have generated a novel fusion protein using GMCSF and an N-terminal truncated version of MCP1/CCL2 (6-76) [hereafter GMME1] and investigated its utility as a CCR2-specific tumoricidal agent.</p> <p>Results</p> <p>We found that distinct to full length CCL2 or its N-truncated derivative (CCL2 5-76), GMME1 bound to CCR2 on mouse lymphoma EG7, human multiple myeloma cell line U266, or murine and human medulloblastoma cell lines, and led to their death by apoptosis. We demonstrated that GMME1 specifically blocked CCR2-associated STAT3 phosphorylation and up-regulated pro-apoptotic BAX. Furthermore, GMME1 significantly inhibited EG7 tumor growth in C57BL/6 mice, and induced apoptosis of primary myeloma cells from patients.</p> <p>Conclusion</p> <p>Our data demonstrate that GMME1 is a fusokine with a potent, CCR2 receptor-mediated pro-apoptotic effect on tumor cells and could be exploited as a novel biological therapy for CCR2⁺malignancies including lymphoid and central nervous system malignancies.</p