MGM Resorts International Chairman and CEO Jim Murren, who led the casino giant’s growth into new markets nationally and internationally while solidifying the company’s leadership on the Las Vegas Strip, said Wednesday he would step down from his positions as soon as a successor is named. The unexpected news came at the outset of MGM’s fourth quarter earnings announcement. In a statement, MGM Resorts said the board had formed a committee of independent directors to conduct the search process for a new CEO. A timetable was not given.