Transfer of chromosome 18 into human head and neck squamous carcinoma cells: evidence for tumor suppression by Smad4/DPC4.

Cytogenetic, allelotype, and somatic cell hybrid studies of human head and neck cancers had suggested that the long arm of chromosome 18 might carry a tumor suppressor gene locus. To directly test this hypothesis, we introduced a wild-type copy of chromosome 18 into FaDu-Hyg-R head and neck squamous carcinoma cells. Five of 10 chromosome 18 hybrid clones formed invasive carcinomas in nude mice at a significantly lower rate and after a longer latency than the parental tumor cells, whereas the five remaining clones were tumorigenic. These results indicate that tumor formation was suppressed by chromosome 18. A homozygously deleted region of 18q in FaDu-Hyg-R cells included the candidate tumor suppressor gene, Smad4/DPC4, and extended into the DCC tumor suppressor gene locus, but not Smad2/MADR2. Each of the hybrid cell lines carried a full-length donor copy of the DCC gene, independently of their capability to form tumors in vivo. In contrast, each of the hybrid clones that were either completely or partly suppressed carried an intact copy of Smad4/DPC4, whereas this gene was deleted in the two most highly tumorigenic clones. Furthermore, the presence of Smad4/DPC4 correlated with partial restoration of cellular responsiveness to transforming growth factor beta. These results provide strong evidence for tumor suppression by Smad4/DPC4.