Fig. 8: Summary depicting the effects of BTG2^/TIS21 gene on the downregulation of Twist1 translation.

Reciprocal immunoprecipitation analysis confirmed the interaction of C-terminal of Twist1 to BTG2^/TIS21 box B domain, which had been screened by protein chip analysis. In the present assay, cNOT7 binding to BTG2^/TIS21 was employed as the interaction control. Adenoviral transfer of BTG2^/TIS21 gene into TNBC cells significantly reduced Twist1 protein, but not mRNA, expression and exhibited inhibition of Twist1 activity regulating E-cadherin and N-cadherin expressions. BTG2^/TIS21-mediated Twist1 protein loss was due to the failures of protein translation by inhibiting cap-dependent initiation via reduced mTORc1 activity and p-eIF2α maintenance, and by collapse in 80S polysome formation. That could lead to failure of protein translation at the initiation step. In addition, BTG2^/TIS21 reduced in vivo and in vitro expressions of eukaryotic elongation factor 1 (eEF1) isoforms and eEF2. All the mechanisms could be confirmed by cDNA microarray data, RT-qPCR, and immunoblotting analyses in the TNBC cells, BTG2^/TIS21-KO mice, and human breast cancer tissues. Taken altogether, BTG2^/TIS21 gene inhibited the initiation and elongation steps of Twist1 translation. Thus, cancer progression including EMT phenomenon can be reduced in the cells with BTG2^/TIS21 high expresser. In conclusion, the BTG2^/TIS21-mediated Twist1 protein loss exhibited better prognosis in the relapse-free survival of malignant breast cancers than that in the lower BTG2^/TIS21 and higher Twist1 expressers