Background: PUF60 is a splicing variant of far upstream element binding protein 1-interacting repressor, which is abnormally expressed in a variety of tumors and is closely involved in their progression. However, whether PUF60 participates in the occurrence and development of breast cancer remains unknown. Therefore, the objective of the current study is to explore the effects and mechanism of PUF60 in the progression of breast cancer. 
Methods: PUF60 expression patterns in breast cancer tissues and cells were determined by RT-PCR and Western blotting. The relationship between PUF60 expression and patients’ clinical features and outcome was evaluated to assess the potential of PUF60 as a marker for progression and prognosis prediction. CCK-8, flow cytometry, transwell and in vivo tumor formation assays were used to detect cell proliferation, apoptosis, migration, invasion and tumorigenesis. The effects of PUF60 on the activation of PTEN/PI3K/AKT were also evaluated by Western blotting and immunofluorescence assays. 
Results: The expression of PUF60 was elevated in breast cancer tissue samples and cell lines, and its high expression was closely associated with the high incidence of lymph node metastasis and advanced TNM stage. Besides, upregulation of PUF60 with lentivirus infection significantly increased the growth, migration, and invasion and repressed the apoptosis of breast cancer HCC1937 and MDA-MB-231 cells, while silencing of PUF60 with shRNA showed the opposite results. Moreover, PUF60 upregulation promoted the expression of p-AKT, PI3K, and mTOR, while decreased PTEN expression through inhibiting its stability and enhancing its ubiquitination. Furthermore, upregulation of PUF60 promoted the tumorigenesis in vivo, whereas this effect was impaired when PTEN expression was upregulated in MDA-MB-231 and HCC1937 cells. 
Conclusion: This study demonstrates that PUF60 is highly expressed in breast cancer; upregulation of PUF60 accelerates the progression of breast cancer through PTEN inhibition.
Keywords: PUF60, PTEN, PI3K/AKT, breast cancer, proliferation, tumorigenesis