Abstract: The Piwi proteins, a class of Argonaute protein family, are predominantly present in different species of the male testes. It can associate with a novel class of small RNAs known as Piwi-interacting RNAs （piRNAs）, lead to transposon gene repression, so that to protect genome integrity and functions of germline stem cell, these plays an important role in self-renewal of germline stem cell, gametogenesis and embryo development. In addition, Piwi proteins was reported to be expressed in various types of human tumor tissue including breast, gastrointestinal and cervical cancer, especially, it is stably expressed in cancer stem cell. Inhibiting its expression can suppress tumor cell proliferation and apoptosis through a variety of different mechanisms, indicating that it might play an important role in tumor initiation and progression. Here is to make a review of the mechanism of Piwi proteins regulate gene expression and its relations with tumorigenesis.

Key words: Neoplasms, Stem cells, Neoplastic stem cells, Piwi proteins