The telomeric repeat binding protein 1 (TRF1) is a major factor of the mammalian telosome/shelterin and negatively regulates telomere length by inhibiting access of telomerase at telomere termini in telomerase-positive cells. In telomerase-negative cancer cells, TRF1 also plays a critical role in the mechanism called alternative lengthening of telomeres (ALT) and is essential for formation of the ALT-associated PML bodies (APBs). It was reported that TRF1 can be degraded by the ubiquitin-proteasome pathway, involving in two regulation factors, Fbx4 and RLIM. Here, we reported that beta-TrCP1, a member of the F-box family protein with ubiquitin ligase activity, is a novel TRF1-associating protein. beta-TrCP1 interacts with TRF1 in vivo and in vitro and promotes its ubiquitination. Overexpression of beta-TrCP1 reduces endogenous TRF1 protein levels, while inhibition of beta-TrCP1 by siRNA stabilizes TRF1. Moreover, we found that beta-TrCP1 is essential for regulation of promyelocytic leukemia body recruitment of TRF1 in U2OS cells. These results reveal that beta-TrCP1 is involved in the negative regulation of TRF1 and represents a new pathway for APB formation in telomerase-negative cells. (c) 2013 Elsevier Inc. All rights reserved.