Interleukin-12 elicits a non-canonical response in B16

Oncogenesis rewires signaling networks to confer a fitness advantage to malig- 18 nant cells. For instance, the B16F0 melanoma cell model creates a cytokine sink for 19 Interleukin-12 (IL-12) to deprive neighboring cells of this important anti-tumor immune 20 signal. While a cytokine sink provides an indirect fitness advantage, does IL-12 provide 21 an intrinsic advantage to B16F0 cells? Functionally, stimulation with IL-12 enhanced 22 B16F0 cell survival but not normal Melan-A melanocytes that were challenged with 23 a cytotoxic agent. To identify a mechanism, we assayed the phosphorylation of pro- 24 teins involved in canonical IL-12 signaling, STAT4, and cell survival, Akt. In contrast 25 to T cells that exhibited a canonical response to IL-12 by phosphorylating STAT4, 26 IL-12 stimulation of B16F0 cells predominantly phosphorylated Akt. Mechanistically, 27 the differential response in B16F0 cells is explained by both ligand-dependent and 28 ligand-independent aspects to initiate PI3K-AKT signaling upon IL12RB2 homod- 29 imerization. Namely, IL-12 promotes IL12RB2 homodimerization with low affinity and IL12RB2 overexpression promotes homodimerization via molecular crowding on 31 the plasma membrane. Collectively, the data suggest that B16F0 cells shifted the intra- 32 cellular response to IL-12 from engaging immune surveillance to favoring cell survival. 33 Identifying how signaling networks are rewired in model systems of spontaneous origin 34 can inspire therapeutic strategies in humans.