Epigen is the latest addition to the mammalian family of EGFR
ligands.
Epigen was initially identified as a novel expressed sequence tag with homology to the
EGF family by high throughput sequencing of a mouse keratinocyte
complementary DNA library, and received its name for its ability to act as an
epithelial mitogen. In vitro studies attributed to
epigen several unique features, such as persistent and potent
biological actions involving low affinity receptor binding, as well as sub-maximal receptor activation and inactivation. Similarly to the other EGFR
ligands, the expression of
epigen is up-regulated by
hormones and in certain
cancer types. While the
biological functions of
epigen remain to be uncovered, it appears to play a role in epidermal structures, such as the mammary gland and the sebaceous gland. The latter organ, in particular, was greatly enlarged in transgenic mice overexpressing
epigen. Interestingly, mice lacking
epigen develop and grow normally, probably due to functional compensation by other EGFR
ligands. Future studies are likely to reveal the
biological roles of the unique receptor binding properties of
epigen, as well as its potential harnessing during disease.