CD38/CD31 interactions activate genetic pathways leading to proliferation and migration in chronic lymphocytic leukemia cells

Abstract

Human CD38 is a pleiotropic glycoprotein belonging to a family of enzymes/receptors involved in the catabolism of extracellular nucleotides. CD38-receptor activities are regulated through binding to the nonsubstrate ligand CD31. CD38 expression above a critical threshold is a negative prognostic marker for chronic lymphocytic leukemia (CLL) patients. Activation of CD38 by means of agonistic monoclonal antibodies or the CD31 ligand induces proliferation and immunoblast differentiation of CLL cells. Here we define the genetic signature that follows long-term in vitro interactions between CD38(+) CLL lymphocytes and CD31(+) cells. The emerging profile confirms that the CD31/CD38 axis activates genetic programs relevant for proliferative responses. It also indicates a contribution of this pathway to the processes mediating migration and homing. These results further support the notion that the CD31/CD38 axis is part of a network of accessory signals that modify the microenvironment, favoring localization of leukemic cells to growth-permissive sites.

Figure 1. CD38 engagement by the CD31 ligand triggers genetic pathways leading to cell proliferation and movement

Venn diagram showing the strategy selected to identify the signature in response to CD31/CD38 interactions. Results were obtained by applying error-weighted Student two-sample paired t-test with Benjamini and Hochberg p-value adjustment to “L-CD31⁺ vs L-mock”, “L-CD31⁺ vs basal” and “L-mock vs basal” class comparisons. Circle radii are proportional to the number of transcripts differentially expressed in each condition. The grey area defines the CD31/CD38 signature. A cut-off of 0.01 for the adjusted p-value was applied to exclude genes that changed expression simply as a result of co-culture (“L-mock vs basal”), while a more stringent threshold (adjusted P<0.001) was applied to the other two comparisons. The resulting 1,645 sequences are involved in 85 differentially regulated pathways identified by PLAGE. 30% of these pathways are implicated in lymphocyte adhesion/movement and/or signalling.

Figure 2. Representation of the expression pattern of 85 pathways differentially expressed as a consequence of CD31/CD38 interactions

Hierarchical clustering was applied to the matrix of the activity levels of the 85 KEGG pathways found as differentially expressed in the L-CD31⁺ samples as compared to the basal and L-mock ones by PLAGE analysis.

Figure 3. Representation of the 7 apoptosis-related genes differentially expressed upon CD31/CD38 engagement

Expression pattern of 7 genes of the 1,645 gene signature that are also part of the 30 apoptosis-regulating genes reported in (14). Red squares refer to up-regulation in the sample with respect to the Universal Reference, while green squares to down-regulation. Expression ratios are represented in a log10 scale. All the genes but Mcl-1 increase their expression as a consequence of CD31/CD38 interactions. Two different Agilent probes specific for Bax are over-expressed in the L-CD31⁺ condition.