EXPRESSION AND ALTERNATIVE SPLICING OF THE DELETED IN COLORECTAL-CANCER (DCC) GENE IN NORMAL AND MALIGNANT-TISSUES

The DCC (deleted in colorectal cancer) gene was identified because it is affected by somatic mutations in colorectal tumors, including allel ic losses in greater than 70% of cancers and localized mutations in a subset of cases. The DCC gene also may be inactivated in other tumor t ypes, including cancers of the pancreas, stomach, breast, prostate, an d brain, as well as some leukemias. We have characterized DCC compleme ntary DNAs obtained from human fetal brain tissues and IMR32 human neu roblastoma cells. Based on the fetal brain complementary DNA sequence, the predicted transmembrane DCC protein product has 1447 amino, acids . The extracellular domain of about 1100 amino acids has four immunogl obulin-like domains and six fibronectin type III-like domains; the 325 -amino acid cytoplasmic domain does not show similarity to previously characterized proteins. Comparison of DCC complementary DNAs from IMR3 2 cells to those from fetal brain identified two potential alternative splice sites. Studies of adult mouse tissues revealed that DCC trancr ipts were present at very low levels in all tissues studied, and alter native splicing of DCC transcripts was seen in some tissues. Immunoblo tting and immunoprecipitation studies with DCC-specific antisera ident ified protein species with molecular weights of approximately 175,000- 190,000 in some rodent tissues and human tumor cell lines. DCC protein expression was highest in brain tissues and neural crest-derived cell lines and markedly reduced or absent in the majority of cancer cell l ines studied. Treatment of DCC-expressing cells with tunicamycin decre ased the apparent molecular weight of the immunoreactive proteins, est ablishing that DCC is a glycoprotein. The studies presented here demon strate that the DCC gene encodes several related glycoprotein species that are likely to be expressed at very low levels in many normal adul t tissues. Furthermore, the absence of DCC expression in some of the c ancer cell lines studied may result from genetic inactivation of DCC.