Extra Copies of GLI1 Gene at 12q13.12 Are Detected in a Subset of Cases of Trisomy 12 Negative Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphomas
C Milito, FA Khokhar, K Newton, RR Singh, F Kasbidi, E Schlette, H Yao, I Biasoli, LJ Medeiros, D Jones, R Luthra, F Vega. MD Anderson Cancer Center, Houston, TX
Background: Trisomy 12 is detected in approximately 20-30% of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). Previously, a structural analysis of chromosome 12 in CLL identified a minimally gained region limited to bands 12q13-15. Glioma-associated oncogene homologue-1 (GLI1) gene, at 12q13, encodes one of the effectors that mediate sonic hedgedog (SHH) signalling. Abnormal expression of GLI1 is observed in several cancers. Here, we report frequent extra copies of GLI1 in trisomy 12 negative CLL.
Design: We analyzed GLI1 (12q13) and WNT1 gene (12q14.3) copy number using real-time qPCR in a series of 71 BM or PB specimens involved by CLL. This set of cases included 53 cases without trisomy 12 and 18 cases with trisomy 12. Expression of SHH and GLI1 was assessed immunohistochemically (IHC) in 22 cases as well as in additional 11 LN involved by SLL. The biological effect of inhibition of SHH signaling pathway on CLL cells was assessed using cell viability assays after treatment with SHH inhibitors, cyclopamine and SANT1. CD19+ non-neoplastic B-lymphocytes collected from the peripheral blood of 4 healthy donors were used as controls.
Results: Extra copies of the GLI1 gene were detected in 21 (39.6%) of 54 CLL cases without trisomy 12; 15 (71.4%) cases had 1 extra copy and 6 (28.5%) had at least 2 extra copies of GLI1. In contrast, 1 extra copy of WNT1, a more telomeric gene than GLI1, was noted only in trisomy 12 cases. The presence of either trisomy 12 or extra copies of the GLI1 gene correlated with strong nuclear expression of GLI1 as detected by IHC (p<.001). In cases with extra copies of GLI1, most of the CLL cells exhibited moderate to strong nuclear expression of GLI1; however, in cases without trisomy 12 or without extra copies of GLI1 gene, expression of GLI1 was restricted to prolymphocytes and paraimmunoblasts. Pharmacologic inhibition of SHH signaling decreased cell viability of CLL cells, but not that of non-neoplastic B-lymphoid cells. Extra copies of GLI1 correlated with high RAI stages (p=.0067).
Conclusions: Extra copy numbers of GLI1 gene are frequent in trisomy 12 negative CLL cases; they can be predicted by IHC and their presence correlate with a high RAI stage. This data also suggests that SHH signaling has a role in the survival of CLL cells.
Monday, March 9, 2009 8:15 AM
Platform Session: Section D, Monday Morning