The ankyrin repeat-containing adaptor protein Tvl-1 is a novel substrate and regulator of Raf-1

Tvl-1 is a 269-amino acid ankyrin repeat protein ex pressed primarily in th ymus, lung, and testes that was identified by screening a murine T-cell two -hybrid cDNA library for proteins that associate with the serine-threonine kinase Raf-1. The interaction of Tvl-1 with Raf-1 was confirmed by co-immun oprecipitation of the two proteins from COS-1 cells transiently transfected with Tvl-1 and Raf-1 expression constructs as well as by co-immunoprecipit ation of the endogenous proteins from CV-1 and NB2 cells. Tvl-1 interacts w ith Raf-1 via its carboxyl-terminal ankyrin repeat domain, The same domain also mediates Tvl-1 homodimerization, Tvl-1 was detected by immunofluoresce nce in both the cytoplasm and the nucleus suggesting that in addition to Ra f-1 it may also interact with nuclear proteins. Activated Raf-1 phosphoryla tes Tvl-1 both in vitro and in vivo. In baculovirus-infected Sf9 insect cel ls, Tvl-1 potentiates the activation of Raf-1 by Src and Ras while in COS-1 cells it potentiates the activation of Raf-1 by EGF. These data suggest th at Tvl-1 is both a target as well as a regulator of Raf-1. The human homolo gue of Tvl-1 maps to chromosome 19p12, upstream of MEF2B with the two genes in a head to head arrangement.