ABSTRACT
BACKGROUND: Telomere maintenance is an important factor in tumorigenesis. PinX1 is a potent telomerase regulator which also involves in telomerase loading to telomeres. Nucleophosmin (NPM) can partially attenuate PinX1 inhibition of telomerase activity and NPM loading to hTERT requires PinX1. However, the role of the PinX1/NPM interaction in telomerase activity is not fully understood. METHOD: The long-term effects of PinX1 and NPM down-regulation on telomere length were investigated by TRF assay. The localization of the PinX1/NPM association and the NPM/PinX1/hTERT complex formation were examined by immunofluorescence studies. RESULTS: Concurrent long-term down-regulation of PinX1 and NPM led to a substantial decrease in telomere length. The interaction with PinX1 was crucial in NPM localization in the nucleolus during the S phase. PinX1 and NPM associated throughout S phase and the NPM/PinX1/hTERT complex formation peaked during the early-S phase. The PinX1/NPM interaction was shown to localize away from Cajal Bodies at the start of S phase. CONCLUSION: PinX1/NPM interaction is important in telomerase regulation during catalysis. NPM is recruited to hTERT by PinX1 and is required in the proposed telomerase modulating unit to activate telomerase when telomere extension occurs during S phase.
ABSTRACT
Telomerase activation and telomere maintenance are critical for cellular immortalization and transformation. PIN2/TERF1-interacting telomerase inhibitor 1 (PinX1) is a telomerase regulator and the aberrant expression of PinX1 causes telomere shortening. Identifying PinX1-interacting proteins is important for understanding telomere maintenance. We found that PinX1 directly interacts with nucleophosmin (NPM), a protein that has been shown to positively correlate with telomerase activity. We further showed that PinX1 acts as a linker in the association between NPM and hTERT, the catalytic subunit of telomerase. Additionally, the recruitment of NPM by PinX1 to the telomerase complex could partially attenuate the PinX1-mediated inhibition on telomerase activity. Taken together, our data reveal a novel mechanism that regulates telomerase activation through the interaction between NPM, PinX1 and the telomerase complex.
Subject(s)
Nuclear Proteins/metabolism , Telomerase/metabolism , Tumor Suppressor Proteins/metabolism , Cell Cycle Proteins , Cell Line , Enzyme Activation , Humans , Multiprotein Complexes , Nuclear Proteins/chemistry , Nucleophosmin , Protein Binding , Protein Conformation , Protein Interaction Domains and Motifs , Telomerase/antagonists & inhibitors , Telomerase/chemistry , Tumor Suppressor Proteins/chemistryABSTRACT
Telomerase recruitment to telomere is the prerequisite for telomere extension, but the proteins involved in this process are still largely unknown. PinX1 is a telomerase inhibitor and has been implicated in telomere maintenance. Silencing of PinX1 significantly reduced the localization of telomerase to telomere during mid-late S phase, suggesting the involvement of PinX1 in the cell cycle-dependent trafficking of hTERT to telomere. We also revealed that PinX1 mediated the chromosomal localization of hTERT during anaphase. This study revealed the role of PinX1 in telomerase function regulation by mediating its localization inside cells.
