CD138- multiple myeloma cells express high level of CHK1 which correlated to overall survival in MM patient

Abstract

Multiple myeloma (MM) is a disease in which abnormal plasma cells proliferate and secrete monoclonal immunoglobulin in the bone marrow. The main characteristic of plasma cells is the expression of the cell surface antigen syndecan-1 (CD138). However, the expression of CD138 is limited to terminally differentiated plasma cells during B cell development. A small subpopulation (2~5%) of human MM cells that lack CD138 expression has been shown to possess enormous proliferation potential in vitro experiment and in animal models, and they also can differentiate into CD138⁺ plasma cells. Thus, this small subset of MM cells was regarded as myeloma cancer stem cell (MCSC). However, its characteristics associated with the pathogenesis of MM remain unclear. In this study, we analyzed the gene expression data of CD138 cell lines downloaded from Gene Expression Omnibus (GEO) database. Limma package in RStudio was used to identify differentially expressed genes (DEGs). Genes enrichment and protein-protein interaction (PPI) network analysis were performed on DAVID and STRING databases. Furthermore, overall survival (OS) analysis in MM patient was utilized to screen out the hub-genes closely associate with the MM pathogenesis process. Hub-genes expression validation and receiver operating characteristic curve (ROC) analysis was performed in different stages of plasma cell disorder diseases. Finally, we verified these findings in MM patient samples. Through integrated bioinformatics analysis of MM CD138^- and CD138⁺ cell lines, we found that CDC7, CDK1, and CHK1 are highly expressed in CD138^- MM cells. These genes are crucial in the G2/M phase of the cell cycle pathway, which is closely related to the malignant proliferation in various tumor cells. Of note, we found that patients with high expression of CDC7, CDK1, and CHK1 had shorter overall survival time. The expression of CHK1 was significantly increased in MM cells compared with normal plasma cell (NPC) and MGUS. More importantly, we further clarified that the expression of CHK1 in release/refraction MM (R/R MM) has obviously increased compared with new diagnosed MM (ND MM).

Keywords: CD138; CHK1; bioinformatics; cancer stem cell; multiple myeloma.

Figure 1

(A) Volcanic map of DEGs distribution. The abscissa of volcano map is the logarithmic value of the fold change (FC) of each sample, and the ordinate is the logarithm of 10 corresponding to the P value of the corresponding sample Negative values, the red and blue dots respectively represent genes that are up-regulated and down-regulated, and the grey dots represent genes that are not significantly different. (B) The expression heat map of the genes in cell cycle pathway. Red represents high gene expression and blue represents low gene expression.

Figure 2

Functional analysis of differential genes. (A) Molecular function analysis of differential genes. (B) KEGG signal pathway of differential genes.

Figure 3

Protein-protein interaction network. Each node represents a gene; Node size represents the degree value; Edge size represents the combined score; Low value to blue and high value to red.

Figure 4

Kaplan-Meier survival curves of MM patient. (A) Kaplan-Meier analysis for overall survival of CDK1; (B) Kaplan-Meier analysis for overall survival of CDC7;(C) Kaplan-Meier analysis for overall survival of CHK1.

Figure 5

Expression validation of the hub genes in NPC (5), MGUS (20) and MM (41). (A) expression of CDC7; (B) expression of CDK1; (C) expression of CHK1.

Figure 6

(A) ROC of CDC7, CDK1 and CHK1 in MGUS, (B) ROC of CDC7, CDK1 and CHK1 in MM.

Figure 7

Verification of CHK1 expression in HC, ND MM, and R/R MM samples. (A) mRNA expression of CHK1 in HC, NDMM and R/R MM samples were analyzed using qRT-PCR. The mRNA expression level of CHK1 was showed by relative expression level. (B) Western blot analysis of the protein expression of CHK1 in ND MM, and R/R MM samples. (C) Results of western blot analysis showing a drastic increase in R/R MM. P< 0.05 was considered statistically significant (*p<0.05, **P<0.01, ***P<0.001, ****P<0.0001).

Figure 8

ATR-CHK1 and ATM-CHK2 in the cell cycle pathway.