CRIPTO ENHANCES THE TYROSINE PHOSPHORYLATION OF SHC AND ACTIVATES MITOGEN-ACTIVATED PROTEIN-KINASE (MAPK) IN MAMMARY EPITHELIAL-CELLS

Cripto-1 (CR-1), a recently discovered protein of the epidermal growth factor (EGF) family; was found to interact with a high affinity, satu rable binding site(s) on HC-11 mouse mammary epithelial cells and on s everal different human breast cancer cell lines. This receptor exhibit s specificity for CR-1, since other EGF-related peptides including EGF , transforming growth factor cu, heparin-binding EGF-like growth facto r, amphiregulin, epiregulin, betacellulin, or heregulin beta 1 that bi nd to either the EGF receptor or to other type 1 receptor tyrosine kin ases such as erb B-3 or erb B-4 fail to compete for binding, Conversel y, CR-1 was found not to directly bind to or to activate the tyrosine kinases associated with Shc EGFR, erb B-2, erb B-3, or erb B-4 either alone or in various pairwise combinations which have been ectopically expressed in Ba/F3 mouse pro-B lymphocyte cells. However, exogenous CR -1 could induce an increase in the tyrosine phosphorylation of 185- an d 120-kDa proteins and a rapid (within 3-5 min) increase in the tyrosi ne phosphorylation of the SH2-containing adaptor proteins p66, p52, an d p46 She in mouse mammary HC-11 epithelial cells and in human MDA-MB- 453 and SKBr-3 breast cancer cells. CR-1 was also found to promote an increase in the association of the adaptor Grb2-guanine nucleotide exc hange factor-mouse son of sevenless (mSOS) signaling complex with tyro sine-phosphorylated She in HC-11 cells. Finally, CR-1 was able to incr ease p42(erk-2) mitogen-activated protein kinase (MAPK) activity in HC -11 cells within 5-10 min of treatment. These data demonstrate that CR -1 can function through a receptor which activates intracellular compo nents in the ras/raf/MEK/MAPK pathway.