Correlation of differential expression of NALP7 and NALP11 with glucocorticoid sensitivity in multiple myeloma cell lines

Abstract

19516 Background: Glucocorticoids (GC) are effective anti-myeloma therapy. However, GC-resistance almost invariably develops. To study the mechanism of GC-resistance in multiple myeloma, we compared the gene expression profiles of the clinically relevant myeloma clones derived from the same patient which are either sensitive (MM.1S) or resistant (MM.1R) to GC-induced apoptosis and growth inhibition. Methods: The MM.1 cell lines were previously described. cDNA microarray analysis was conducted using the GeneChip Human Genome U133 Plus 2.0 Array (Affymetrix). Gene expression of individual genes were analyzed by quantitative real-time PCR using gene- specific primer-probe sets (Applied Biosystems), with relative gene expression level normalized to an internal control (RNaseP). Gene knock- down or overexpression was achieved by transfecting MM.1 cells with gene-specific siRNA (Invitrogen) or cDNA expression construct, respectively. Results: By cDNA microarray analysis, we identified NALP7 and NALP11 among the few genes that showed most significant differential levels of expression between the sensitive and resistant myeloma lines. Both genes belong to the NALP gene family implicated in innate immunity. We confirmed with qPCR that NALP7 expression was significantly decreased whereas NALP11 expression was markedly increased in GC-resistant MM.1 cells compared to the GC-sensitive MM.1 cells. We further showed that both genes are down-regulated by GC treatment. Next, we investigated the biological significance of the NALP genes by altering the NALP gene expression level using transfection. Suppression of NALP7 by siRNA-mediated gene knock-down or exogenous overexpression of NALP11, either alone or in combination, did not alter the GC-sensitivity of MM.1S cells, suggesting that altering NALP7 and NALP11 expression is not sufficient to induce GC resistance. Conclusions: Our studies demonstrated that the differential expression of two NALP family genes, NALP7 and NALP11, correlates with GC sensitivity in myeloma, and that both genes are regulated by glucocorticoid signaling. The biological significance of their differential regulation in myeloma remains to be determined. No significant financial relationships to disclose.