High Expression of the Endoplasmic Reticulum Protein MZB1 predicts Inferior Prognosis in Chronic Lymphocytic Leukemia, Follicular Lymphoma and Diffuse Large B-Cell Lymphoma and Is Associated with a Unique Gene Expression Profile,

The marginal zone B and B1 cell-specific protein (MZB1) was recently described as a key regulator of the secretion of IgM molecules, the control of calcium homeostasis and integrin-mediated adhesion in B-lymphocytes. We recently identified MZB1 gene expression as a novel prognostic factor being part of a highly significant 8 gene expression signature in chronic lymphocytic leukemia (CLL). Since several neoplasm's derive from mature B-lymphocytes and differ in clinical behavior and prognosis, but share unique functions like immunoglobulin production and secretion we asked whether these different diseases share common molecular mechanisms and prognostic factors. Here, we show that MZB1 expression is a novel, strong prognostic factor in a variety of B-cell neoplasm's.

We analyzed 106 previously untreated and 33 relapsed CLL patients by quantitative PCR and correlated the MZB1 gene expression with overall survival (OS), time to treatment (TTT) and known risk factors of CLL. To expand the study on other hematological malignancies we additionally analyzed the public available gene expression data sets of follicular lymphoma (FL; GSE16131; n=184), diffuse large B-cell lymphoma (DLBCL; GSE10846; n=414), multiple myeloma (MM; GSE2658, n=559), and acute myeloid leukemia (AML; GSE12417; n=306). To adjust for clinical variables, multivariate Cox model were fitted to the respective data sets. To identify genes strongly correlated with MZB1 expression levels, we compared the CLL, DLBCL, FL and AML datasets and performed a multistep correlation analysis.

High MZB1 expression was a significant parameter of inferior prognosis in previously untreated (OS: HR: 1.63 (CI: 1.14–2.33), p=0.007; TTT: HR: 1.43 (CI: 1.13–1.81), p=0.003) and relapsed CLL patients (OS: not significant; TTT: HR: 1.48 (CI: 1.12–1.95), p=0.005) and was associated with known clinical and molecular parameters including unmutated IGVH status (p<0.001) and advanced Binet stage (Binet A vs. C p=0.001). Thus, due to the high correlation with IGVH status, MZB1 expression remained not an independent factor in multivariate models including both factors. In addition, MZB1 expression was also a predictor of OS in FL (221286_s_at HR: 1.16 (CI: 0.98–1.37) p=0.086; 223565_at: HR: 1.3 (CI: 1.1–1.61) p=0.015) and DLBCL (221286_s_at: HR: 1.17 (CI: 1.06–1.3) p=0.003; 223565_at: HR: 1.21 (CI: 1.08–1.35) p=0.001) but not in other hematologic malignancies like MM or AML. Again, high MZB1 expression levels correlated with prognostic markers in both, FL and DLBCL. However, a multivariate analysis in DLBCL including the International Prognostic Index (IPI), the gene expression subtype of DLBCL and MZB1 expression (continuous) confirmed MZB1 as an independent predictor of OS. Similar results were obtained from a multivariate analysis in follicular lymphoma including MZB1 expression (continuous) and IPI. We also identified genes that closely correlated with MZB1 expression in CLL, FL, DLBCL and AML based on the multistep correlation analysis. We compared the four datasets using these genes and observed that FL, DLBCL, and CLL show stronger similarity to each other than to the AML group. Interestingly, the ratio of probesets positively correlated to MZB1 expression levels to negatively correlated probesets was the highest in the AML group (CLL=3.69; FL=3.4; DLBCL=0.60; AML=78.7). The similarity of the lymphoma subsets was further strengthened by the analysis of the deregulated pathways based on these genes. Among the top seven pathways deregulated only in CLL, FL, and DLBCL were protein processing in endoplasmic reticulum, endocytosis, MAPK signaling pathway and Fc gamma R-mediated phagocytosis.

In conclusion we discovered a novel prognostic marker that predicted OS in all analyzed malignancies of mature B-cell origin and showed additional prognostic value in multivariate analysis in both, FL and DLBCL. The differential analysis of genes co-expressed with MZB1 further strengthened the prognostic relevance of MZB1 across different mature B-cell diseases. Due to its biological function in neoplasm's of mature B-cell origin and the potential involvement in known oncogenic pathways MZB1 may represent a target for future therapeutic interventions.

No relevant conflicts of interest to declare.