Clinical significance of human endogenous retrovirus K (HERV-K) in multiple myeloma progression

Human endogenous retroviruses (HERVs) are retrotransposons that infect human germline cells and occupy 5–8% of the human genome. Their expression, though inhibited by mutation, deletion, and epigenetic mechanisms under normal conditions, is associated with diseases including cancer. This study aimed to clarify the association between HERVs and multiple myeloma (MM) progression. We found that HERV-K envelope (env) and long-term repeat (LTR) expression was statistically significantly higher within plasma cells in MM than in monoclonal gammopathy of undetermined significance or controls. HERV-K env knockdown increased proliferation in the MM.1S cell line and decreased the expression of the tumor suppressor genes TP53 and CDKN1A. TP53 and CDKN1A were highly expressed in MM, and their expression was correlated with HERV-K expression. HERV-K knockdown reduced apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3F, 3G, and 3H expression by 10–20% in MM.1S cells. The anti-retroviral agents nevirapine and nelfinavir suppressed proliferation and increased HERV-K expression in MM cell lines. Our results suggest that HERV-K is involved in MM progression, but its role is likely to go beyond promoting cell proliferation. Clarifying the role of HERV-K in MM will lead to the discovery of novel treatment strategies and supply new insights into MM pathogenesis.