We previously identified km23 as a novel TGFbeta receptor-interacting protein. 
Here we show that km23 is ubiquitously expressed in human tissues and that 
cell-type specific differences in endogenous km23 protein expression exist. In 
addition, we demonstrate that the phosphorylation of km23 is TGFbeta-dependent, 
in that EGF was unable to phosphorylate km23. Further, the kinase activity of 
both TGFbeta receptors appears to play a role in the TGFbeta-mediated 
phosphorylation of km23, although TGFbeta RII kinase activity is absolutely 
required for km23 phosphorylation. Blockade of km23 using small interfering RNAs 
significantly decreased key TGFbeta responses, including induction of 
fibronectin expression and inhibition of cell growth. Thus, our results 
demonstrate that km23 is required for TGFbeta induction of fibronectin 
expression and is necessary, but not sufficient, for TGFbeta-mediated growth 
inhibition.