Marrow Stromal Cells Induce TCL1 Expression in Chronic Lymphocytic Leukemia B Cells.

Abstract 2347

Poster Board II-324

The human T cell leukemia/lymphoma 1 (TCL1) oncogene was initially identified as a target of chromosomal translocations and inversions at the 14q32.1 chromosome breakpoint region in T-cell prolymphocytic leukemia (T-PLL). Increased TCL1 expression is seen in follicular lymphoma, Burkitt lymphoma, diffuse large B-cell lymphoma, and chronic lymphocytic leukemia (CLL). Transgenic mice over-expressing TCL1 under control of the mu immunoglobulin gene enhancer develop a CD5⁺ B cell lymphoproliferative disorder that mimics human CLL, indicating that TCL1 plays a central and/or causal role in the pathogenesis of CLL. However, chromosome aberrations that constitutively activate TCL1 have not (yet) been identified in the vast majority of CLL patients, and therefore the oncogenic mechanism(s) of TCL1 activation in CLL remain unclear. There is growing evidence that external signals from the microenvironment control and regulate the survival and proliferation of CLL cells. Marrow stromal cells (MSC) are highly effective in protecting CLL cells from spontaneous and drug-induced apoptosis, and are used as a model system to study the marrow microenvironment. In order to explore the molecular cross talk between CLL cells and MSC, we co-cultured CLL cells with different MSC and analyzed gene expression changes induced by co-cultures with MSC, an approach similar to our recent study with nurselike cells (Blood 113:3050-8, 2009). For this, RNA was extracted from 19-purified CLL cells from 10 different patients (baseline expression, day 0). Also, the same patients' samples were co-cultured on stroma cells (KUSA-H1, NK-Tert) for 2 and 7 days. At these time points, RNA again was isolated after CD19-purification. Then, gene expression was determined using HG U133 plus 2.0 oligonucleotide arrays from Affymetrix. Gene expression changes were analyzed in individual patients' samples, comparing baseline samples' gene expression to samples after 2 and 7 of co-culture on MSC. We observed relatively homogeneous gene expression changes in CLL cells after co-culture with MSC. We found that TCL1 was among the top 5 genes that were most highly up-regulated by MSC, based on at least 3-fold up-regulation in at least 6 of the paired samples. We also found an up-regulation of TCL1 at the protein level when assessed by immunoblotting and flow cytometry in CLL samples after co-culture with MSC. These findings indicate that MSC can induce and regulate TCL1 expression in CLL, suggesting that the microenvironment plays an even greater role in the pathogenesis of this disease than previously recognized.