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

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.Experimental Design: We analyzed the role of BIRC3 mRNA expression in primary CLL samples in correlation to clinical datasets and used ex vivo 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 in vitro.

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.