Subrings invariant under endomorphisms

Let S and R be the rings of regular functions on affine algebraic varieties over a field of characteristic 0, R be embedded as a subring in S, and F :S→S be an endomorphism such that F(R) R. Suppose that every ideal of height 1 in R generates a proper ideal in S, and the spectrum of R has no self-intersection points. We show that if F is an automorphism so is FR :R→R. When R and S have the same transcendence degree then the fact that FR is an automorphisms implies that F is an automorphism.