TWEAK is a member of the TNF family and was first described as a weak inducer of apoptosis in demonstrates that this relatively small molecule is a fully transformed cell lines. Recently, a receptor for TWEAK was isolated by expression cloning from a HUVEC cell cDNA library. TweakR is a small protein belonging to TNF receptor super family. TweakR is capable of intiating a proliferative signal by biding to TRAF1, 2, and 3. TweakR mRNA is upregulated during tissue regeneration in aorta and liver. It may also play a role in vascular cell migration and angiogenesis.