I've written before about actors and personalities who are shy or uncomfortable speaking in public, and I've written about my own shyness in some social settings and my trick of playing a character (me) to overcome it.
Here's another example of a shy person who managed to become an enormous success over six decades as a film and television actor: Charlton Heston. In an interview with Robert Osborne on TCM, he said,
"I suppose on a certain level, I am a shyer man than my public persona suggests. I have learned to be a public person and I'm very comfortable with that identity; it's that man that's talking to you now. But I am also a rather private man, and actors are not supposed to be private men, so I've invented a public Charlton Heston as well."
There were two Charlton Hestons, the public man and the private man. But how different do you suppose they were? I imagine the main difference was in his comfort level, not in any aspect of his personality that might or might not change in different situations -- at least that's how my public persona works.
For me, once my public persona becomes comfortable in a situation, then the "whole me" becomes comfortable, and I can let the persona go and just be me. Read about how I do it here.
And remember: you're not the only one who's nervous in front of a crowd, holding a microphone, or being interviewed. Many, many people who live their lives in the spotlight are just as nervous as you are. They've developed tools to make themselves more comfortable in those situations, and so can you!