Full length
mRNA to a
drug-inhibited cell surface
NADH oxidase, tNOX or ENOX2, is present in both non-
cancer and
cancer cells but is translated only in
cancer cells as alternatively spliced variants. ENOX2 is a growth-related
protein of the external plasma membrane surface that is shed into the circulation and is inhibited by a series of
quinone site inhibitors with anticancer activity. To test the possibility that ENOX2 expression might be important to early stages of non-
cancer cell development, the expression of the
protein was monitored in chicken embryos during their development. Polyclonal
antisera to a 34 kDa human serum form of ENOX2 cross-immunoreactive with the
drug-responsive
NADH oxidase of chicken
hepatoma cells was used. The
protein was identified based on
drug-responsive enzymatic activities and analyses by western blots. The
drug-responsive activity was associated with plasma membranes and sera of early chicken embryos and with chicken
hepatoma plasma membranes but was absent from plasma membranes prepared from livers or from sera of normal adult chickens and from late embryo stages. The findings suggest that ENOX2 may fulfill some functions essential to the growth of early embryos which are lost in late embryo stages and absent from normal adult cells but which then reappear in
cancer.