I am trying to auto add each word or words divided by comma into an existing url.

I have url lets say http://stackoverflow.com/search?q=HERE IS THAT TEXT.

I have this function:

function movie_cast( $atts, $content = null ) {
    return '<div class="movie_cast">Cast: '.$content.'</div>';
}

add_shortcode( 'movie_cast', 'movie_cast' );

I am using it: [movie_cast]Actor 1, Actor 2[/movie_cast]

Output from this is just text: Actor 1, Actor 2

How can I get otput it like this: <a href="http://stackoverflow.com/search?q=Actor 1">Actor 1</a>, <a href="http://stackoverflow.com/search?q=Actor 2">Actor 2</a>