It's a partnership of Phil Anschutz's sports and entertainment company and the boxer's Golden Boy Promotions. The idea is to use AEG's assets (it owns or is affiliated with nearly 100 venues worldwide) and Golden Boy's roster of 50 fighters. From the LAT:

AEG Chairman Tim Leiweke said discussions of a possible union have been going on since De La Hoya fought Mosley at AEG's Staples Center in 2000. Schaefer said those negotiations intensified in the last few years. Earlier this year, De La Hoya bought a piece of Major League Soccer's Houston Dynamo franchise from AEG. And last week, it was announced that a seven-foot-tall bronze statue of De La Hoya would join those of Wayne Gretzky and Magic Johnson outside Staples Center. Leiweke celebrated the Golden Boy deal not only for the addition of De La Hoya to a sports-entertainment empire that includes Kobe Bryant and David Beckham but also because of his own enthusiasm for the sport.

There are no details on AEG's investment, other than it calls for a double-digit percentage of Golden Boy. Already, there are plans to have Golden Boy's David Haye fight at AEG's O2 Arena in London later this year. De La Hoya started the company in 2001.