BIRC3 Expression Predicts CLL Progression and Defines Treatment Sensitivity via Enhanced NF-κB Nuclear Translocation.

Abstract

Chronic lymphocytic leukemia (CLL) pathophysiology is characterized by a complex crosstalk of tumor cells with the microenvironment. In this regard, NF-κB signaling is considered as important signaling axis, with a variety of key molecules aberrantly expressed or genetically altered in patients with CLL. One of these molecules is BIRC3 (cIAP2), a central regulator of noncanonical NF-κB signaling that serves as pathway brake in the absence of microenvironmental signals. However, the contribution of BIRC3 expression to CLL progression and potential therapeutic implications is unknown.<b>Experimental Design:</b> We analyzed the role of BIRC3 mRNA expression in primary CLL samples in correlation to clinical datasets and used <i>ex vivo</i> assays to investigate functional consequences on the level of NF-κB signaling and downstream target gene regulation. For proof-of-principle experiments, we used genetically modified cell lines. We demonstrate that patients with CLL with low BIRC3 expression experience a more rapid disease progression, which coincides with an enhanced activation of canonical NF-κB target genes evidenced by an increased p65/Rel-B nuclear translocation ratio. As a consequence of enhanced canonical NF-κB target gene activation, both anti- and proapoptotic Bcl-2 family members were upregulated in BIRC3^low primary CLL cells, which was associated with higher sensitivity to venetoclax treatment <i>in vitro</i>. Here we show the impact of BIRC3 expression in CLL disease progression in the absence of BIRC3 mutations and show altered canonical NF-κB target gene activation with therapeutic implications.