Growth Factor, Independent 1B (GFI1B)

Gfi1b was downregulated in myelomonocytic M1 cells in the presence of interleukin-6 (IL6). However, forced expression of Gfi1b inhibited IL6-induced cell cycle arrest and differentiation and inhibited expression of the p21(WAF1) (CDKN1A) promoter. The inhibition was attributed to a transcriptional repressor contained in the Gfi1b SNAG domain.

Gfi1b encodes a 330-amino acid zinc finger protein with a SNAG repressor domain. Gfi1b is 97% identical in the zinc finger domain and 95% identical in the SNAG domain to Gfi1. Northern blot analysis showed that Gfi1b is expressed in bone marrow and spleen but not in kidney, liver, lung, heart, or brain. In contrast, Gfi1 is expressed primarily in bone marrow and thymus.GFI1B is spread over 5 kb and contains 6 coding exons.