Background: Monoclonal gammopathy of undetermined significance (MGUS) is characterized by plasma cell production of abnormal monoclonal protein, or M protein. While MGUS itself is asymptomatic, it generally carries a 1% per year risk to progression to multiple myeloma (MM). The etiology of MGUS, as well as why it progresses to MM in some cases, remains unclear. Moreover, it is not known why some MGUS patients, such as African Americans, have higher risk to progression to MM. Contrasting MGUS and MM can potentially highlight genes that differentiate benign gammopathies from malignant ones and may be involved in disease progression from MGUS to MM.
Methods: We employed our STARGEO platform to tag samples from the NCBI Gene Expression Omnibus and performed two separate meta-analysis to compare MGUS and MM transcriptomes. For the first meta-analysis, we tagged MGUS plasma cells recovered from the bone marrow of 101 patients and tagged plasma cells from 64 healthy subjects as a control. For the second analysis. We tagged CD138+ cells from the bone marrow of 383 MM patients and used the MGUS tagged samples as a control. We then analyzed the signature in Ingenuity Pathway Analysis (IPA).
Results: From our first meta-analysis of MGUS, we identified EIF2 signaling, regulation of EIF4 and p70S6K signaling, and JAK/STAT signaling as top canonical pathways. Top upstream regulators included TP53, TGFB1, and the proto-oncogene MYCN and MYC (with predicted activation). The most upregulated genes included pro-oncogenes such as KIT and MLLT3, which is well-studied in acute leukemia but not yet described in MGUS. Another top upregulated gene was NRG3, a myeloma growth factor. Additionally, our analysis highlighted key genes involved in transcription and epigenetic regulation. For example, there was upregulation of RBFOX2, which is involved in alternative splicing during oncogenesis and tumor progression, and of PARP15, a transcriptional repressor with poly(ADP-ribose) polymerase activity and candidate gene for drug targeting. Also, there was upregulation of the DNA damage-inducible gene GADD45A, found to promote global DNA methylation. Lastly, we found upregulation of COMMD3, a gene with a recently identified role in humoral activity and B cell migration.
From our second meta-analysis comparing MM and MGUS directly, we identified mitochondrial dysfunction, oxidative phosphorylation, purine nucleotides de novo biosynthesis, and sirtuin signaling as top upstream regulators. Like our first analysis, TP53 (with predicted inhibition), TGFB1, and MYC (with predicted activation) were top upstream regulators. The most upregulated gene was NUP62, a nucleoporin and novel regulator of cell proliferation and inducer of MYC activity. Our analysis also illustrated pro-oncogenic signaling pathways such as the Wnt pathway through upregulation of the ubiquitin ligase RNF14 and serine/threonine kinase through upregulation of SRPK2. Moreover, we found upregulation of the super-enhancer DUSP4, a phosphatase whose over-activity may drive MM severity. Lastly, we found upregulation of lysosomal associated membrane protein LAMP5. LAMP5 was recently identified in single-cell RNA sequencing of MM patients and may play a significant role in disease.
Conclusions: Our study illustrates signaling pathways in MGUS that are present in MM such as EIF2, JAK/STAT, and MYC signaling. We also illustrate gene activity in MGUS that may predispose to MM progression such as NRG3, RBFOX2, and PARP15. GADD45RA and COMMD3 may play novel roles in MGUS. Our second analysis highlighted disease activity that persist from MGUS to MM, such as MYC signaling. It is possible that the genes from this analysis that aims to distinguish MM from MGUS may be responsible for tipping the scales from benignity to malignancy. Genes such as DUSP4, RN14, LAMP5, and others could serve as novel biomarkers or targets to MM and risk of progression of MGUS to MM.
Disclosures
No relevant conflicts of interest to declare.
Clinical, morphological, and cell kinetic differences among multiple myeloma, monoclonal gammopathy of undetermined significance, and smoldering multiple myeloma
