Evaluation of NCAM and DKK1 Expression in Multiple Myeloma and MGUS by Gene and Tissue Microarrays: Expression Accompanies Progression.

Introduction: Expression NCAM1, a cell adhesion molecule involved in neuron-neuron adhesion, is also expressed by multiple myeloma (MM PC). Osteolytic bone lesions are a hallmark of MM and elevated expression of NCAM in MM PC has been correlated with this process (Ely and Knowles, 2003). We have previously reported that MM PC express DKK1 and MM blocks osteoblast differentiation in a DKK1-specific manner, suggesting that secretion of the Wnt signaling inhibitor plays a role in MM bone disease. Herein we used gene expression microarrays and tissue microarrays (TMAs) to investigate the simultaneous expression of DKK1 and NCAM in MM and MGUS.

Methods: The study population consisted of 198 newly diagnosed MM and 44 MGUS. RNA from CD138-selected plasma cells was hybridized to Affymetrix U133Plus microarrays and data processed with Affymetrix Microarray Suite GCOS1.1 software. TMAs were constructed from formalin-fixed, paraffin embedded bone marrow biopsies. Serial sections of TMA were immunostained for CD138, NCAM and DKK1. TMAs were scanned using ScanScope using 20x lens, assessed using TMA lab software (Aperio Technologies) and scored as an average number of cells in the context of CD138 staining.

Results: When put in context of a recently described molecular classification (Zhan et al., 2006), NCAM and DKK1 were found significantly co-over-expressed (DKK1+/NCAM+) in HYPERDIPLOID MM (P < 0.01); NCAM+/DKK1− was typical for MMSET-spike MM (P<0.001); NCAM−/DKK1+ DKK1 was characteristic of MM in MAF-spike disease (P < 0.001), CCND1 spikes with co-expression of CD20 (P<0.01), and the so-called MYELOID subgroup (P<0.001). In contrast, virtually all cases of MGUS were DKK1−/NCAM-. On TMAs, DKK1 expression varied in CD138-positive cells in MM, and in osteocytes and megakaryocytes in MM and MGUS, but was clearly negative in osteoblasts/lining cells. NCAM expression, was also variably expressed in PC of MM cases and in virtually 100% of osteoblasts/lining cells in both MM and MGUS. Osteocytes were distinctly negative for NCAM in both diseases. Of 195 analyzable MM biopsies, PC were DKK1+ in 1% to > 90% of PC in 191 (98%); of these, 94 were also NCAM+ in 5% to > 90% of PC; 1 case was positive for NCAM+/DKK− and 3 were NCAM−/DKK−. There was no significant difference in clinical parameters and survival in a comparison of NCAM+/DKK+ and NCAM−/DKK+ groups. DKK1 gene expression was higher in DKK1+/NCAM+ than in DKK1+/NCAM− MM (P=0.006); NCAM gene expression was higher in DKK1+/NCAM+ than in DKK+/NCAM− MM (P<0.0001) and NCAM was the number one SAM-defined gene over-expressed in DKK1+/NCAM+ relative to DKK1+/NCAM− disease. Consistent with GEP data, DKK1+/NCAM+ MM was over-represented in HYPERDIPLOID MM (32% v. 10%; P<0.001), while DKK1+/NCAM− disease was overrepresented in MAF-spike (15% v. 2%; P=0.003) and MYELOID subgroups (32% v. 18%; P=0.03). DKK1+/NCAM+ MM was completely absent in CCND1-spike /CD20-negative disease, with only 4% of DKK1+/NCAM− cases in this subgroup. No difference was observed for the other subtypes.

Conclusion: DKK1 is expressed in all cases of MM with half also expressing NCAM. Neither gene is expressed in MGUS PC. These data suggests that expression of these genes in plasma cells accompanies disease progression.