The MDM2 SNP309 genotype influencing MDM2 expression levels was identified as an additional independent risk factor in B-CLL. Targeting MDM2-p53 interactions might emerge as a successful treatment strategy for B-CLL.

The Hedgehog (Hh) pathway regulates cell proliferation and survival and contributes to tumorigenesis. We investigated the expression and function of this pathway in B-cell chronic lymphocytic leukemia (CLL) cells and in healthy B lymphocytes. Profiling of cognate Hh pathway members revealed reduced expression of two key Hh signaling effectors, Smoothened (SMOH) and GLI, in CLL cells, whereas transcription levels of other investigated members resembled normal B-lymphocyte levels. Examining the functional role of SMOH and GLI in cell survival, we found that CLL cells were hardly sensitive toward specific SMOH inhibition, but showed an unspecific decline in cell viability in response to high concentrations of the SMOH antagonist cyclopamine. In contrast, treatment with the novel GLI antagonist GANT61 reduced expression of the target gene Patched and preferentially decreased the viability of malignant cells. Specific RNA interference knockdown experiments in a CLL-derived cell line confirmed the autonomous role of GLI in malignant cell survival. GANT61-induced apoptosis in primary leukemic cells was partly attenuated by protective stromal cells, but not soluble sonic hedgehog ligand. In summary, our data show a downregulation of the classical Hh pathway in CLL and suggest an intrinsic SMOH-independent role of GLI in the ex vivo survival of CLL cells.

IntroductionB-cell chronic lymphocytic leukemia (B-CLL) is a neoplastic disease of slowly proliferating CD5 ϩ B cells that develops in the older population. Its clinical behavior is variable, with some patients having an indolent course without any therapy and others a rapidly progressing one probably requiring aggressive treatment. As an underlying mechanism of differential disease activity, genomic aberrations 1 and distinct expression levels of signaling molecules influencing survival as well as proliferation of B-CLL cells have been postulated. Besides the B-cell receptor itself 2,3 and Zap-70, a tyrosine kinase involved in B-cell receptor (BCR) signaling, 4 CD38, initially described as a mediator of leukocyte adhesion to endothelium, 5 was identified as a further candidate, since it induces both survival and proliferation signals in B-CLL cells 6 and its expression and signaling capacity correlate with both progression and response to therapy. 7 Its clinical importance as negative prognostic marker was established by analysis of CD38 expression in large patient cohorts. [7][8][9][10] While the study of malignant cells provides many insights into tumor biology, it has also become clear that transformation and progression of tumors is not an independent process but is controlled by their interactions with the tumor microenvironment (for a recent review see Joyce 11 ). Supporting factors in the microenvironment include stromal and vascular cells as well as infiltrating immune cells. Dependency on such supportive signals should also be relevant in B-CLL, in which close cooperation with other immune cells can be expected from normal behavior of B cells. In the present study, we focused on T cells and their expression of CD38 for the following reasons. (1) CD38 has been identified as an important signaling molecule of T cells. 12 (2) The signaling capacity of T cells has been shown to be dysregulated in B-CLL patients (for a review see Scrivener et al 13 ). Such an aberrant immune control might favor a more aggressive outgrowth of the neoplastic B-cell clone and negatively impact on the clinical outcome of patients. (3) T cells might even deliver antiapoptotic and/or proliferative signals to the neoplastic clone when coming into intimate contact with each other in lymphoid compartments like bone marrow or lymph nodes. 14 We therefore raised the question of whether aberrant expression of CD38 in T cells might also be of prognostic relevance in B-CLL. Patients, materials, and methods Patients and samplesThe study was approved by the local ethics committees (those of the Medical University Innsbruck and Provincial Government of Salzburg, Austria) and conducted according to the Declaration of Helsinki. After providing informed patient consent, 204 consecutive, unselected B-CLL For personal use only. on May 11, 2018. by guest www.bloodjournal.org From patients seen at the Department of Hematology and Oncology, University Hospitals Innsbruck and Salzburg, Austria, between March 2000 and November 2005 were included in t...

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