HILI is a 973 amino acid protein encoded by the human gene PIWIL2. HILI belongs to the argonaute family and contains one PAZ domain and one PIWI domain. HILI is a cytoplasmic protein that is expressed in adult testis and in most tumors. It regulates spermatogenesis and primordial germ cell production and has an essential role in meiotic differentiation of spermatocytes and in self-renewal of spermatogonial stem cells. Expression of HILI can modulate expression of genes involved in stem cell proliferation (such as PDGFR-b), in energy metabolism (such as Glut1), in cell-cell interaction (such as Integrin a6, GJA7, THY-1 and CD9), and in germ cell differentiation (such as STRA8). It may also play a role as a regulatory factor of Stat3/Bcl-xS/L/CCND1 pathway. Repression of HILI can inhibit tumor cell growth. HILI acts as an oncogene by inhibition of apoptosis and promotion of proliferation in tumors.