use Lingua::EN::NameCase qw( nc );

use strict;

while (<DATA>) {
	s/(?<=AU: )(.*)/nc $1/e;
	print;
}

__DATA__
AU: jane smith
AU: JOHN DOE
AU: keith miller
AU: PHILLIP LEIGH-WILLIAMS
AU: PAUL MCCARTNEY
AU: DOUGIE O'CALLAGHAN
AU: MARIE ST. JOHN
AU: henry viii