Gene Expression Profile of Circulating Myeloma Cells Reveals CD44 and CD97 (ADGRE5) Overexpression

Introduction: Release of the aberrant plasma cells (PC) from the bone marrow (BM) and their presence in the peripheral blood (PB) is a maker of disease progression and worse survival in multiple myeloma (MM) (Nowakowski et al., 2005). Circulating plasma cells (cPCs) are able to survive without homing microenvironment, evade the original tumor and colonize other bone marrow niche. Detailed analysis of various surface proteins showed that cPCs display decreased levels of integrins, adhesion molecules N-CAM (CD56) and the stem cell factor receptor (Paiva et al., 2013). Comprehensive analysis of the genome-wide gene expression profiling that could provide deeper insight into the expression patterns of cPCs of MM is still lacking.

Aims: To identify differentially expressed genes in paired samples of aberrant plasma cells from BM and PB and to describe potential biomarkers of cPCs in MM.

Material and methods: Ten patients with multiple myeloma (seven new diagnoses and three relapses) have been included in the study after signing the informed consent form. Paired samples of aberrant plasma cells from bone marrow and peripheral blood were obtained from each patient. Aberrant plasma cells (aPCs) were sorted according to the immunophenotype as CD45^dim/CD38⁺/CD19^-/CD56^-/+ cells. Gene expression profiling (GEP) was performed on paired samples using Affymetrix GeneChip Human Gene ST 1.0 array. RMA normalized data at gene level were analyzed using Wilcoxon paired test with Benjamini-Hochberg multiple testing correction.

Results: The median infiltration of aberrant PC in the BM was 27.5% (range 1.1 - 93%) and 1.2% (range 0.19 - 2.8%) for cPCs in the PB. The median level of M-protein was 32.35 g/l (range 18.6 - 62.2 g/l). GEP analysis of paired BM and PB samples revealed 1001 significantly changed genes in cPCs (adjusted p-value<0.05). Gene ontology analysis did not reveal any significantly affected pathways. Nevertheless, two genes upregulated in cPCs, ADGRE5 and CD44, can be suggested as biologically relevant potential biomarkers of cPCs (Figure 1).

Conclusion: The infiltration of aPCs in the bone marrow does not correlate with the amount of cPCs (p=0.16). Among differentially expressed genes, two surface markers upregulated in cPCs are of particular interest: CD44 and ADGRE5 (CD97). The CD44 antigen is a cell-surface glycoprotein involved in cell-cell interactions, cell adhesion and migration. Moreover, CD44 contribute to lenalidomide resistance in multiple myeloma (Bjorklund et al., 2014). CD97 is encoded by ADGRE5 gene and belongs to the EGF-TM7 subgroup of adhesion G-protein-coupled receptors. The expression of CD97 has been linked to invasive behavior in thyroid and colorectal cancer. Moreover, higher CD97 expression levels have been detected in 54% (208/385) of primary AML samples based on flow cytometric analysis (Wobus et al., 2015). Nevertheless, neither ADGRE5 nor CD97 expression were described in plasma cell dyscrasia previously. Thus, despite non-systemic changes of gene expression at the whole transcriptome level, cPCs in MM likely represent distinct biological entity with specific expression profile underlying advanced PC malignant transformation. To confirm the results, flow cytometric analysis on the bigger cohort will be performed.

Acknowledgment: This study was supported by Institutional Development Plan of University of Ostrava (IRP201550) and The Ministry of Education, Youth and Sports (Specific university research of the Faculty of Medicine, University of Ostrava) project no. SGS03/LF/2015-2016, Ministry of Health Czech Republic RVO-FNOs/2014/17P and RVO-FNOs/2016/21.

Figure 1

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Genes of interest differentially expressed in the bone marrow (BM) versus peripheral blood (PB) aberrant plasma cells.

Figure 1

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Genes of interest differentially expressed in the bone marrow (BM) versus peripheral blood (PB) aberrant plasma cells.

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