Dec 21 (Reuters) - U.S. movie studio MGM Holdings is exploring a sale, the Wall Street Journal reported on Monday, citing people familiar with the matter. The movie studio behind the “James Bond” franchise has tapped investment banks Morgan Stanley and LionTree LLC and started a formal sale process, the newspaper reported. The company has a market value of around $5.5 billion, based on privately traded shares and including debt, according to the report on.wsj.com/38qIWfN. MGM Holdings did not immediately respond to a Reuters request for comment. (Reporting by Kanishka Singh in Bengaluru; Editing by Maju Samuel)