Tribbles-Related Protein Family Members as Regulators or Substrates of the Ubiquitin-Proteasome System in Cancer Development

Tribbles-related protein (TRB) family members are the mammalian orthologs of Drosophila tribbles. Tribbles was originally identified as a cell cycle regulator during Drosophila development. Tribbles genes are evolutionary conserved, and three TRB genes (TRB1, TRB2 and TRB3) have been identified in mammals. TRBs are considered pseudokinases because they lack an ATP binding site or one of the conserved catalytic motifs essential for kinase activity. Instead, TRBs play important roles in various cellular processes as scaffolds or adaptors to promote the degradation of target proteins and to regulate several key signaling pathways. Recent research has focused on the role of TRBs in tumorigenesis and neoplastic progression. In this review, we focus on the physiological roles of TRB family members in tumorigenesis through the regulation of the ubiquitin-proteasome system and discuss TRBs as biomarkers or potential therapeutic targets in cancer.