UPDATE 1-Itaú-CorpBanca merger plan draws fire from U.S. investor

SAO PAULO/NEW YORK, March 4 (Reuters) - An activist U.S. investor has asked Chilean bank CorpBanca SA to reconsider its approval of a merger with Brazil's Itaú Unibanco Holding SA and to launch a new auction, alleging CorpBanca had sold its minority investors short while benefiting its key shareholder.