tRNA-derived fragments and tRNA halves: The new players in cancers.

tRNA-derived fragments (tRFs) and tRNA halves (tiRNAs) are small non-coding RNAs derived from precursor tRNAs or mature tRNAs. Depending on the sources, tRFs can be divided into tRF-1, tRF-2, tRF-3, tRF-5, and i-tRF; tiRNAs can be divided into 5'tiRNA and 3'tiRNA. Both tRFs and tiRNAs play important roles in tumorigenesis. Some tRFs and tiRNAs promote cell proliferation and cell cycle progression by regulating the expression of oncogenes. Other tRFs and tiRNAs inhibit cancer progression. Mechanism studies have shown that tRFs and tiRNAs may bind to RNA binding proteins such as Y-box binding protein 1 (YBX1) and prevent transcription, inactivate initiation factor eIF4G/A, promote translation of ribosomal proteins, or activate aurora kinase A, the regulator of mitosis. Therefore, tRFs and tiRNAs regulate the occurrence and development of cancers, including lung cancer, colorectal cancer, prostate cancer, breast cancer, ovarian cancer, B cell lymphoma, chronic lymphocytic leukemia, etc. This article reviews the classification of tRFs and tiRNAs, their biological functions in the occurrence of cancers, and their relationships with some common cancers. It will provide new ideas for the diagnosis and treatment of cancers.