NCIt definition : SPI1 is an oncogene specifically activated in acute murine erythroleukemias, induced
by the Friend spleen focus forming virus. It encodes the transcription factor PU.1,
normally expressed in all hematopoietic lineages except in T-cells. An ETS-domain
transcription factor essential for the development of myeloid (osteoclast progenitors)
and B-lymphoid cells. Graded expression of this transcription factor appears to specify
distinct cell fates in the hematopoietic system. A low concentration of PU.1 protein
induces the B-cell fate, whereas a high concentration promotes macrophage differentiation.
PU.1 is thought to regulate transcription of FMS and CD18/11B, proteins central to
the osteoclast phenotype, and is required for p47-phox promoter activity in myeloid
cells. PU.1 expression is increased with the induction of osteoclastogenesis by 1,
25-dihydroxyvitamin D3. The human gene is located at 11p11.2.;