The Anti-Proliferative Activity of BTG/TOB Proteins Is Mediated via the Caf1a (CNOT7) and Caf1b (CNOT8) Deadenylase Subunits of the Ccr4-Not Complex

Abstract

The human BTG/TOB protein family comprises six members (BTG1, BTG2/PC3/Tis21, BTG3/Ana, BTG4/PC3B, TOB1/Tob, and TOB2) that are characterised by a conserved BTG domain. This domain mediates interactions with the highly similar Caf1a (CNOT7) and Caf1b (CNOT8) catalytic subunits of the Ccr4-Not deadenylase complex. BTG/TOB proteins have anti-proliferative activity: knockdown of BTG/TOB can result in increased cell proliferation, whereas over-expression of BTG/TOB leads to inhibition of cell cycle progression. It was unclear whether the interaction between BTG/TOB proteins and the Caf1a/Caf1b deadenylases is necessary for the anti-proliferative activity of BTG/TOB. To address this question, we further characterised surface-exposed amino acid residues of BTG2 and TOB1 that mediate the interaction with the Caf1a and Caf1b deadenylase enzymes. We then analysed the role of BTG2 and TOB1 in the regulation of cell proliferation, translation and mRNA abundance using a mutant that is no longer able to interact with the Caf1a/Caf1b deadenylases. We conclude that the anti-proliferative activity of BTG/TOB proteins is mediated through interactions with the Caf1a and Caf1b deadenylase enzymes. Furthermore, we show that the activity of BTG/TOB proteins in the regulation of mRNA abundance and translation is dependent on Caf1a/Caf1b, and does not appear to require other Ccr4-Not components, including the Ccr4a (CNOT6)/Ccr4b (CNOT6L) deadenylases, or the non-catalytic subunits CNOT1 or CNOT3.

Depletion of poly(A)-specific ribonuclease (PARN) inhibits proliferation of human gastric cancer cells by blocking cell cycle progression

“…Overexpression of Ccr4d/ANGEL2 inhibits the proliferation of MCF-7 cells by elevating p21 mRNA stability [21]. Caf1a/CNOT7 and Caf1b/CNOT8 has been identified to be antiproliferation proteins through binding with B-cell translocation gene proteins (BTG1 and BTG2) [42][43][44][45][46][47]. Ccr4a/CNOT6 and Ccr4b/ CNOT6L contribute to cell survival and the prevention of cell death and senescence [48].…”

Multifunctional roles of the mammalian CCR4–NOT complex in physiological phenomena

“…The interaction with CNOT7/CNOT8 is required for the anti-proliferative activities of Tob proteins in various types of mammalian cells (Horiuchi et al, 2009; Doidge et al, 2012b; Ezzeddine et al, 2012). Importantly, Tob functions as a guide molecule for the CCR4–NOT complex to target mRNAs through an interaction with CNOT7 (Doidge et al, 2012a).…”

Polyethylenimine-coated SPION exhibits potential intrinsic anti-metastatic properties inhibiting migration and invasion of pancreatic tumor cells

“…S5). We also studied the PMag treatment effect in Pan02 cells on transcript levels of the proliferation/migration inhibitors c-Cbl and Tob1 [31,[46][47][48]. PMags induced overexpression of the E3 ubiquitin ligase c-Cbl transcript (Fig.…”