Xinglu
Black Belt
Although I have not found anything that states what a Jew converting to another religion would be considered, the fact that under certain circumstances (depending on which orthodoxy of Judaism you are referring to) you need not practice or obey the laws of the Torah to be considered a Jew.
I see, when I tell you that, it's boulderdash but if a website tells you that it's true... nice talking with you, sir.