International Paper up on plans to sell unit for $1.5 billion
** International Paper's IP.N shares up 2% at $48.06 ** Co to sell its global cellulose fibers unit to American Industrial Partners for $1.5 billion ** IP says it will invest $250 million to upgrade its Riverdale mill in Alabama ** Up to last close, stock was down about 13% YTD (Reporting by Anshi Sancheti in Bengaluru) ((Anshi.Sancheti@thomsonreuters.com))