Tripping on TRIB3 at the junction of health, metabolic dysfunction and cancer

Abstract

Metabolic diseases like obesity, atherosclerosis and diabetes are frequently associated with increased risk of aggressive cancers. Although metabolic dysfunctions in normal cells are manifested due to defective signaling networks that control cellular homeostasis, malignant cells utilize these signaling networks for their increased survival, growth and metastasis. Despite decades of research, a common mechanistic link between these chronic pathologies is still not well delineated. Evidences show that the unfolded protein response (UPR) and the endoplasmic reticulum stress (ERS) pathways are often dysregulated in both metabolic diseases and cancer. The UPR also triggers coordinated signaling with both PI3K/AKT/mTOR and Autophagy pathways in order to promote stress-adaptive mechanisms. Whereas, uncontrolled UPR and the resultant ERS escalates cells towards metabolic dysfunctions and ultimately cell death. In this review, we will discuss findings that implicate a crucial role for the multifunctional ERS-induced protein, TRIB3. The 'pseudokinase' function of TRIB3 facilitates the inactivation of multiple transcription factors and signaling proteins. The MEK1 binding domain of TRIB3 enables it to deactivate multiple MAP-kinases. In addition, the COP1 motif of TRIB3 assists ubiquitination and proteasomal degradation of numerous TRIB3 associated proteins. The most well studied action of TRIB3 has been on the PI3K/AKT/mTOR pathway, where TRIB3-mediated inhibition of AKT phosphorylation decreases insulin signaling and cell survival. Conversely, cancer cells can either upregulate the AKT survival pathway by suppressing TRIB3 expression or alter TRIB3 localization to degrade differentiation inducing nuclear transcription factors such as C/EBPα and PPARγ. The gain-of-function Q84R polymorphism in TRIB3 is associated with increased risk of diabetes and atherosclerosis. TRIB3 acts as a crucial 'stress adjusting switch' that links homeostasis, metabolic disease and cancer; and is being actively investigated as a disease biomarker and therapeutic target.

Keywords: Autophagy; Cancer; ER-stress; Metabolic syndrome; PI3K/AKT/mTOR; TRIB3.