Gene expression analysis in aggressive NHL

Two newly characterized germinal center B-cell-associated genes, GCET1 and GCET2, have differential expression in normal and neoplastic B cells

A group of genes are highly expressed in normal germinal center (GC) B cells and GC B-cell-derived malignancies based on cDNA microarray analysis. Two new genes, GCET1 (germinal center B-cell expressed transcript 1) and GCET2, were cloned from selected expressed sequence tags (IMAGE clone 1334260 and 814622, respectively). GCET1 is located on chromosome 14q32 and has four splicing isoforms, of which the longest one is 1787 bp and encodes a 435-amino acid protein. GCET2 is located on 3q13.13, and the cloned fragment is 3270 bp, which encodes a protein of 178 amino acids. Blast search showed that GCET1 has a highly conserved serine proteinase inhibitor (SERPIN) domain and is located on a chromosomal locus containing seven other SERPIN family members. GCET2 is a likely homologue of the mouse gene M17, a GC-expressed transcript. Analysis of the GCET2 protein sequence indicated that it may be involved in signal transduction in the cytoplasm. Northern blot and real-time polymerase chain reaction analyses confirmed that GCET1 is highly restricted to normal GC B cells and GCB-cell-derived cell lines. Although GCET2 is also a useful marker for normal and neoplastic GC B cells, it has a wider range of expression including immature B and T cells. Real-time polymerase chain reaction assay showed that both GCET1 and GCET2 are preferentially expressed in follicular lymphoma and diffuse large B-cell lymphoma with GC B-cell differentiation, confirming previous microarray gene expression analysis, but neither one is entirely specific. Multiple markers are necessary to differentiate the GCB from the activated B-cell type of diffuse large B-cell lymphoma with a high degree of accuracy.

Kaposi's sarcoma-associated herpesvirus-induced upregulation of the c-kit proto-oncogene, as identified by gene expression profiling, is essential for the transformation of endothelial cells

Kaposi's sarcoma (KS), the most frequent malignancy afflicting AIDS patients, is characterized by spindle cell formation and vascularization. Infection with KS-associated herpesvirus (KSHV) is consistently observed in all forms of KS. Spindle cell formation can be replicated in vitro by infection of dermal microvascular endothelial cells (DMVEC) with KSHV. To study the molecular mechanism of this transformation, we compared RNA expression profiles of KSHV-infected and mock-infected DMVEC. Induction of several proto-oncogenes was observed, particularly the receptor tyrosine kinase c-kit. Consistent with increased c-Kit expression, KHSV-infected DMVEC displayed enhanced proliferation in response to the c-Kit ligand, stem cell factor (SCF). Inhibition of c-Kit activity with either a pharmacological inhibitor of c-Kit (STI 571) or a dominant-negative c-Kit protein reversed SCF-dependent proliferation. Importantly, inhibition of c-Kit signal transduction reversed the KSHV-induced morphological transformation of DMVEC. Furthermore, overexpression studies showed that c-Kit was sufficient to induce spindle cell formation. Together, these data demonstrate an essential role for c-Kit in KS tumorigenesis and reveal a target for pharmacological intervention.

Burkitt's and Burkitt-like lymphoma

Burkitt's and Burkitt-like lymphoma (BL/BLL) are aggressive B-cell malignancies with a high proliferative rate that may be fatal within months if not treated promptly. Furthermore, treatment of BL/BLL requires comprehensive supportive care to avoid disease-related complications such as acute renal failure secondary to tumor lysis syndrome. Improvements in our understanding of the biology of BL and BLL have led to more effective therapeutic protocols. Clinical trials have demonstrated that short duration, multi-agent, dose-intensive chemotherapy regimens combined with aggressive central nervous system therapy results in long-term survival rates in children and young adults near 70% to 80%, whereas long-term disease-free survival rates in older adults remains suboptimal at 15% to 25%. Outcomes in HIV-associated BL/BLL are improved because of more effective chemotherapy regimens and enhanced HIV care. Autologous bone marrow transplantation has proven feasible in many patient populations with BL/BLL and may lead to cure in selected patients. Improved therapeutic strategies are warranted, such as integrating agents such as monoclonal antibodies to combination dose-intensive chemotherapy. Moreover, further study into the molecular biology of BL/BLL with attention to the role of c-myc dysregulation is needed to help predict prognostic factors and for the development of molecular targeted therapies. Clinical trials remain critical to determine the most effective treatment regimens that will continue to improve cure rates in this aggressive but treatable disease.

Microarray-based expression profiling of normal and malignant immune cells

Recent advances in gene microarray technology have facilitated global analyses of gene expression profiles in normal and malignant immune cells. Great strides have been made in our understanding of molecular differences among various types of immune cells, the process of T and B cell activation, and the genomic changes that convert normal cells to malignant ones. Genomic analysis has become a crucial aspect of cancer classification, diagnosis, therapy, and prognosis. This technology has the potential to reveal the comprehensive transcriptional alterations that dictate fundamental biological processes such as signal transduction in response to specific stimuli, cell growth, differentiation, and apoptosis. While reaping the benefits of genomic analyses, it is important to realize its limitations with respect to accuracy of interpretation, reproducibility, and signal detection. It is crucial to optimize signals for individual probe-target pairs and to develop a uniform set of criteria for data analyses. The development of a public-access database of results from individual laboratories will pave the way for identifying discrepancies and advancing scientific breakthroughs.