[Global gene expression analysis and novel signalling pathways in Hodgkin lymphoma]

To identify pathogenetic mechanisms in Hodgkin lymphoma (HL) we performed global gene expression profiling of four HL derived cell lines and compared the expression profiles with those of normal B cells and B cell non-HL. This analysis revealed a global loss of B-cell specific gene expression in Hodgkin-Reed/Sternberg (HRS) cells (21). Further analysis showed that ABF-1 and Id2, which are both negative regulators of the B cell master transcription factor E2A and likely also Pax-5, are aberrantly expressed in HRS cell lines (11, 17). For Id2, immunohistochemistry showed expression in the HRS cells of all cases, and E2A could be coimmunoprecipitated with Id2 from HRS cell lines, indicating that the aberrant Id2 expression may indeed contribute to the loss of the B-cell specific gene expression in HL (17). An analysis of the global gene expression data for aberrant expression of genes which are frequently involved in neoplastic transformation identified six receptor tyrosine kinases (RTK) aberrantly expressed in HRS cell lines. All RTKs were also (co)-expressed in primary cases and mostly activated by auto- or paracrine mechanisms (18). Analysis of greater number of cases identified a subgroup of HL which encompasses about 20 % of cases characterised by coexpression of at least four of the RTKs. An survey of several B cell lymphoma types with a pan-phospho-tyrosine specific antibody indicated that mediastinal large B-cell lymphoma is beside HL the only entity where aberrant TK activities cause an aberrantly high cellular phospho-tyrosine content in a significant fraction of cases.