Author(s): Christian Barker
Mentor(s): Luuk Heitink, David Huang
Institution BYU
Relapse and refractory disease are common in the treatment of hematologic malignancies. During or after treatment with the BH3-mimetic Venetoclax, this often originates within the lymph node (LN) microenvironment. Resistance in the LN is characterized by dysregulation of pro- and anti-apoptotic BCL2-family proteins, notably upregulation of the pro-survival protein Myeloid Cell Leukemia-1 (MCL1). Activation of the Nuclear Factor-kappa B (NF-κB) signaling cascade has also been observed in the lymph node microenvironment post-Venetoclax treatment. This suggests the role of NF-κB signaling in the transcriptional regulation of MCL1. Previous studies in cell models and patient samples of various hematologic malignancies have yielded mixed insights into the nature of this correlation, with some indicating MCL1 is a direct target of NF-κB and others refuting this relationship. Here we show that MCL1 transcription is not directly linked to NF-κB activation in an acute lymphoblastic leukemia (ALL) cell line. RS4;11 ALL cells treated with known activators of NF-κB (CD40L or TNFα) showed NF-κB activation within 4 hours of exposure, yet no concurrent increase in MCL1 transcription was observed via qPCR between 10 minutes and 24 hours. However, MCL1 protein levels increased, as evidenced by western blotting. RS4;11 double-reporter cells were then developed to assess the correlation between NF-κB activation and MCL1 transcription at the single cell level. Flow cytometry analysis after treatment with TNFα or CD40L for 4-72 hours confirmed that NF-κB activation did not correlate with MCL1 transcription. Intracellular staining for MCL1 protein revealed varying results. Our findings indicate that NF-κB signaling does not directly regulate MCL1 transcription in RS4;11 ALL cells, though it may impact MCL1 protein levels post-transcriptionally through an intermediary mechanism. Identification of this mediator may provide a novel therapeutic target for treatment of Venetoclax-resistant ALL.