Zinc finger protein GFI-1 has low oncogenic potential but cooperates strongly with pim and myc genes in T-cell lymphomagenesis.

The gfi-1 gene encodes a zinc finger containing protein that is specifically expressed in T-lymphocytes and is a frequent target of proviral insertion in T-cell lymphoma provoked by infection with MoMuLV--a non acute transforming retrovirus. Expression of a gfi-1 transgene targeted to T-cells by the lck proximal promoter provokes a reduction of peripheral CD4 and CD8 positive T-cells but nevertheless weakly predisposes transgenic animals for the development of T-cell lymphoma. Forced coexpression of the serine/threonine kinase Pim-1 can partially restore normal T-cell numbers in double pim-1/gfi-1 transgenic mice. Moreover, the combinatorial expression of Pim-1 and Gfi-1 leads to accelerated development of T-cell lymphoma with a mean latency period of 114 days. A similar accelerated rate of lymphoma development was observed when lck-gfi-1 mice were crossed with mice that carry a L-myc gene targeted to be expressed at high levels in T-cells. The results show that gfi-1 can act with low activity as a dominant oncogene when overexpressed but also demonstrate that it is most efficient only in the presence of a cooperative partner protein as for example Pim-1 or L-Myc. In addition, the results suggest that Pim-1 and Gfi-1 are acting synergistically in both T-cell lymphomagenesis and T-cell development.