FOXP3 as an X-linked tumor suppressor.

The FOXP3 gene was initially identified because its mutation caused lethal autoimmune diseases in mice and humans. Mice with heterozygous mutations of FoxP3 (mouse version of the FOXP3 gene) succumb to mammary tumors spontaneously, while those with prostate-specific deletions develop prostate intraepithelial neoplasia. Somatic mutations, deletion, and epigenetic inactivation of FOXP3 are widespread among human breast and prostate cancers. Unlike autosomal tumor suppressor genes that are usually inactivated by mutations in both alleles, X-linked FOXP3 mutations in cancer samples are usually heterozygous, with the wildtype allele selectively inactivated in cancer. This skewed X-inactivation suggests a new approach to reactivation of FOXP3 for cancer therapy.