The inhibition of three distinct signaling pathways eliminates the oncogenic Tribbles homolog 2 from melanoma cells

Tribbles homolog 2 (TRIB2) is one of three members of the Tribbles family of pseudo serine/threonine kinases. It acts as an oncogene whose expression is correlated with tumor progression and therapy resistance in melanoma. TRIB2 has been implicated in conferring resistance to various anti-cancer therapies suggesting TRIB2 as a therapeutic target for resistant tumors. This study explores the pharmacological targeting of TRIB2, revealing several independent routes of pharmacological manipulations. TRIB2 is a short-lived protein stabilized by inhibition of the PI3K/AKT pathway. Conversely, inhibitors of BRAF, MEK and ERK significantly decrease TRIB2 expression by a mechanism that involves transcription. Additionally, Polo-Like Kinases (PLKs) inhibitors significantly reduce TRIB2 protein expression and stability. Strikingly, increasing concentrations of the kinase inhibitor PIK-75 effectively eliminate TRIB2 in melanoma cells surpassing its PI3K inhibitory activity suggesting the destabilizing effect of the inhibition of an unknown kinase. TMT-based proteomics, chemical biology and genetic manipulation revealed CDK12 as the kinase that mediates the destabilizing effect on TRIB2. Overall, we identify three distinct classes of compounds that efficiently eliminate the oncogenic TRIB2 protein from melanoma cells based on different molecular mechanisms and exhibiting 40 to 200 times greater potency than the previously reported afatinib.