Note that Jaime Pressly said that “Ugly Betty” was “big-upping the ugly fat girl,” not that the show was “bigging up the ugly fat girl” (or “bigging the ugly fat girl up“). So we find that big-up is being treated as a single entity that can be inflected with verb endings, rather than as the verb big plus the particle up.
- "Big-Up" on the Rise by Ben Zimmer, OUPblog, 01.24.08
I'm sure my first awareness of "Big-Up" was Biggie Smalls giving "Big-Ups to Brooklyn". Given his Caribbean roots that all makes sense.