The TGFß receptor-interacting protein km23-1/DYNLRB1 plays an adaptor role in TGFß1 autoinduction via its association with Ras.

ABSTRACT

We have previously elucidated the signaling events that are required for TGFß1 autoinduction (Yue, J., and Mulder, K. M. (2000) J. Biol. Chem. 275, 30765-30773). Further, we have reported that the TGFß receptor (TßR)-interacting protein km23-1 plays an important role in TGFß signal transduction (Jin, Q., Ding, W., and Mulder, K. M. (2007) J. Biol. Chem. 282, 19122-19132). Here we examined the role of km23-1 in TGFß1 autoinduction in TGFß-sensitive epithelial cells. siRNA blockade of km23-1 reduced TGFß1 mRNA expression, as well as DNA binding and transcriptional activation of the relevant activator protein-1 site in the human TGFß1 promoter. Further, knockdown of km23-1 inhibited TGFß-mediated activation of ERK and JNK, phosphorylation of c-Jun, and transactivation of the c-Jun promoter. Sucrose gradient analyses indicate that km23-1 was present in lipid rafts together with Ras and TßRII after TGFß treatment. Immunoprecipitation/blot analyses revealed the formation of a TGFß-inducible complex between Ras and km23-1 in vivo within minutes of TGFß addition. Moreover, we demonstrate for the first time that km23-1 is required for Ras activation by TGFß. Our results indicate that km23-1 is required for TGFß1 autoinduction through Smad2-independent Ras/ERK/JNK pathways. More importantly, our findings demonstrate that km23-1 functions as a critical adaptor coupling TßR activation to activation of Ras effector pathways downstream.