Apoptosis-resistant phenotype of classical Hodgkin's lymphoma is not mediated by somatic mutations within genes encoding members of the death-inducing signaling complex (DISC)

Pathogenesis of classical and lymphocyte-predominant Hodgkin lymphoma

Hodgkin and Reed-Sternberg (HRS) cells in classical Hodgkin lymphoma (HL) and lymphocytic and histiocytic (L&H) cells in nodular lymphocyte-predominant HL (NLPHL) are derived from germinal-center B cells. HRS cells have, however, largely lost their B cell phenotype and aberrantly express markers and transcriptional regulators of other hematolymphoid cell types. Deregulation of multiple signaling pathways and downstream transcription factors, including receptor tyrosine kinases, nuclear factor-kappa B (NF-kappaB), and Janus kinase/signal transducer and activator of transcription (JAK/STAT), is a further hallmark of HRS cells. These cells harbor genetic lesions that contribute to or cause increases in the activity of transcription factors of the NF-kappaB and STAT families. HRS cells are found within a mixed reactive cellular infiltrate and interact with these nonmalignant cells in a complex fashion that appears to be essential for HRS cell survival and proliferation. Less is known about the pathogenesis of L&H cells in NLPHL, but increases in the activity of receptor tyrosine kinases, NF-kappaB, and JAK/STAT have also been detected.

Loss of expression of LyGDI (ARHGDIB), a rho GDP-dissociation inhibitor, in Hodgkin lymphoma

The guanosine triphosphatase (GTPase) inhibitor LyGDI (ARHGDIB, Ly/D4-GDI, RhoGDIb or RhoGDI 2) is abundantly expressed in haematopoetic cells and possibly plays a role in the onset of apoptosis. Gene expression profiling of Hodgkin cell lines revealed that LyGDI expression was downregulated in these cell lines. The present study evaluated the expression of LyGDI in Hodgkin cells in vivo and studied the function of LyGDI in Hodgkin cell lines in vitro. Our results showed that virtually all Hodgkin and Reed-Sternberg cells in classical Hodgkin lymphoma lacked LyGDI protein expression. On the other hand, almost all non-Hodgkin lymphomas, except for anaplastic large cell lymphomas, expressed LyGDI protein. Transfection of the classical Hodgkin cell line L428 with a vector containing full-length LyGDI-induced apoptosis in a subset of cells. However, the majority of Hodgkin cells with transgenic expression of LyGDI escaped apoptosis. Our data show that lack of LyGDI expression is a frequent feature of cHL but that it is not of vital importance for the growth and survival of these cells.

Molecular pathogenesis of Hodgkin's lymphoma

According to the WHO classification, Hodgkin's lymphoma (HL) is subdivided into a classical variant and a nodular lymphocyte predominant variant which are characterized by the presence of Hodgkin's and Reed-Sternberg (H-RS) cells or lymphocytic and histiocytic (L&H) cells, respectively. This article reviews genetic characteristics and transcriptional changes of H-RS and L&H cells, including recent knowledge about transforming mechanisms and signaling pathways that contribute to the antiapoptotic phenotype displayed by H-RS and L&H cells. We also discuss major cellular and molecular mediators contributing to the establishment and maintenance of a reactive background in HL-affected tissues. We believe that an in-depth understanding of the pathogenesis of HL will eventually lead to the development of novel biologically based therapeutic strategies in the near future.