Telomeric repeat binding factor 1 (TRF1), also known as TERF1, the shelterin complex, which modulates the telomere structures. TRF1 protein structure contains a C-terminal Myb motif, a dimerization domain near its N-terminus and an acidic N-terminus. Pin2/TRF1 was originally identified as a protein bound to telomeric DNA (TRF1) and as a protein involved in mitotic regulation (Pin2). Pin2/TRF1 negatively regulates telomere length and importantly, its function is tightly regulated during the cell cycle, acting as an important regulator of mitosis. TRF1 can be bound and modulated by two nucleolar GTP-binding proteins, nucleostemin (NS) and guanine nucleotide binding protein-like 3-like (GNL3L), which exhibit apparently opposite effects on the protein degradation of TRF1. TRF1/TERF1 may has association with cancer. TRF1 may play a significant role in cell differentiation in non-small cell lung cancer (NSCLC). The expression level of TRF1 protein is significantly reduced in kidney cancer and the level is negatively correlated with malignant degree of the cancer. TRF1 expression in malignant gliomas cells, may play a role in the malignant progression of astroglial brain tumors.