Pathway incompatibility between NF-κB and RAS signaling constrains oncogenicity in B-cell leukemia

B-cell acute lymphoblastic leukemia (B-ALL) arises from lymphoid precursors that fail to complete normal B-cell maturation and frequently harbor activating mutations in the RAS-ERK pathway that promote leukemic survival and therapeutic resistance. During normal B-cell development, early precursors signal through the precursor B-cell receptor (pre-BCR), which supports survival and proliferation before transitioning to expression of the mature B-cell receptor (BCR). In B-ALL, leukemic blasts are typically arrested prior to BCR expression. Our prior work demonstrated that oncogenic RAS signaling functionally mimics pre-BCR- dependent signaling by inducing BCL6 expression, thereby sustaining leukemic survival and proliferation. Although oncogenesis is often attributed to cooperating mutations, mutually exclusive genetic alterations suggest that certain oncogenic pathways may instead be functionally incompatible. In our previous work, we proposed the concept of pathway incompatibility, in which co-activation of certain oncogenic signaling programs antagonizes their oncogenic activity and suppresses tumorigenesis. Here, we examined the interaction between RAS signaling and canonical NF-{kappa}B activity in B-ALL within this framework. Genomic analysis of leukemia cases revealed significant underrepresentation of samples harboring concurrent RAS and NF-{kappa}B pathway alterations, consistent with negative genetic interaction. Functionally, activation of canonical NF-{kappa}B triggered apoptosis and depletion of RAS-pathway-mutated B-ALL cells in growth competition assays, in contrast to activation of the non-canonical pathway, which conferred a growth advantage. Mechanistically, canonical NF-{kappa}B suppressed pre-BCR-associated signaling programs and increased expression of mature BCR components, indicating a receptor state incompatible with oncogenic RAS activity. Consistent with this framework, RAS oncogenic activity has previously been shown to preferentially support transformation in B-cell precursors lacking surface BCR expression and to be poorly tolerated in mature BCR-positive B cells. In line with this principle, we found that enforced oncogenic RAS signaling was poorly tolerated in BCR-positive lymphoma cells unless surface BCR expression was disrupted. Pharmacologic activation of NF-{kappa}B reduced ERK signaling and selectively impaired viability of RAS-pathway-mutated B-ALL cells, with enhanced effects in combination with ERK inhibition. Together, these findings identify canonical NF-{kappa}B signaling as a developmental context-dependent constraint on RAS-driven leukemogenesis and provide mechanistic support for pathway incompatibility as a determinant of the oncogenicity of signaling pathways.