Tob is a member of an emerging family of anti-proliferative proteins that 
suppress cell growth when over-expressed. tob mRNA is highly expressed in 
anergic T cells and over-expression of Tob suppresses transcription of 
interleukin-2 (IL-2) through its interaction with Smads. Here, we identified two 
types of cDNA clones coding for poly(A)-binding protein (PABP) and inducible 
PABP (iPABP) by screening an expression cDNA library with the GST-Tob probe. 
Co-immunoprecipitation and GST-pull down experiments showed that Tob associated 
with the carboxyl-terminal region of iPABP. We then found that iPABP, like PABP, 
was involved in regulation of translation: iPABP enhanced translation of IL-2 
mRNA in vitro. The enhanced translation of IL-2 mRNA required the 3'UTR and 
poly(A) sequences. Tob abrogated the enhancement of translation through its 
interaction with carboxyl-terminal region of iPABP in vitro. Consistently, 
over-expression of Tob in NIH3T3 cells, in which exogenous iPABP was stably 
expressed, resulted in suppression of IL-2 production from the simultaneously 
transfected IL-2 expression plasmid. Finally, Tob, whose expression was induced 
by anergic stimulation, was co-immunoprecipitated with iPABP in human T cells. 
These findings suggest that Tob is involved in the translational suppression of 
IL-2 mRNA in anergic T cells through its interaction with iPABP.