CYSTEINE-153 AND CYSTEINE-154 OF TRANSMEMBRANE TRANSFORMING GROWTH-FACTOR-ALPHA ARE PALMITOYLATED AND MEDIATE CYTOPLASMIC PROTEIN ASSOCIATION

Transforming growth factor-alpha (TGF-alpha) is synthesized as a trans membrane protein with a highly conserved, short cytoplasmic domain tha t is rich in cysteines. TGF-alpha is a prototype of a large family of growth factors involved in cell-cell communication. We have shown prev iously that transmembrane TGF-alpha associates with a kinase activity and two proteins of 106 and 86 kDa. In this study, we have used site-d irected mutagenesis of the cytoplasmic domain of TGF-alpha to define t he structural requirements for these protein interactions. Whereas the cytoplasmic domain of TGF-alpha was not essential for association wit h transmembrane p106, deletion of the C-terminal 8 amino acids, includ ing a cysteine pair, abolished the interaction with p86 and greatly re duced the kinase activity associated with transmembrane TGF-alpha. Rep lacement of these 2 cysteines by serines similarly reduced the associa tion of p86 with transmembrane TGF-alpha. Using a combination of mutat ional analysis and direct microsequencing, we have determined that thi s cysteine pair was palmitoylated. We therefore conclude that these cy steines play a critical role in the interaction of TGF-alpha with asso ciated proteins and in the function of this protein complex. The palmi toylation of these cysteines suggests a possibly dynamic role of fatty acid modification in the integrity and function of the transmembrane TGF-alpha complex.