I think that English people tend to use acronyms much more than what Italians do; moreover, nowadays, there is a lot of specialized languages each having its own acronyms. Being English the language used worldwide, it is exposed to such inflections way more than other languages.
That being said, I don't know much about game makers but I think that no, the MC would be called protagonista while another character (not the main one) would be called personaggio. Or, even if writing in Italian, a game maker could use MC, but only considering that its intended audience would understand it as a specific term used in that peculiar context.
