PU.1: a crucial and versatile player in hematopoiesis and leukemia.

Purine Rich Box-1 (PU.1)/ SFFV Proviral Integration Site-1 (Spi-1) is an Ets-family transcription factor, which was first characterized as an oncogene in Friend's murine erythroleukemia, and subsequently, as a transcriptional regulator of myeloid promoters. PU.1 has since emerged as a central regulator of all hematopoietic cell lineages. PU.1 is essential for terminal myeloid cell differentiation, B and T cell development, erythropoiesis and hematopoietic stem cell maintenance. These pleiotropic functions are reflected by its complex and dynamic expression pattern during hematopoiesis. Factors regulating this complex expression are only beginning to be revealed. Interestingly, recent work has provided strong evidence that suppression of PU.1 function is critical for the leukemic transformation of myeloid cells, both in mouse and man. Thus PU.1 is a multi-faceted protein that controls numerous normal and pathogenic functions within the hematopoietic system.