PTBP1 and neoplasm: Functioning in the cytoplasm, PTBP1, on the contrary, can inhibit the proliferation and invasion of tumor cells by binding to mRNAs of various tumor suppressors, which leads to the stabilization of such transcripts (tumor necrosis factor CD154 mRNA in activated T lymphocytes [134]); activation of IRES-mediated translation (cyclin-dependent kinase inhibitor protein p27 [135], apoptotic protease activating factor 1, Apaf-1 [136]).