The Dow was lifted by industrial heavyweights, including Boeing BA.N and Caterpillar Inc. CAT.N. By Krystal Hu and Medha Singh May 21 (Reuters) - Wall Street closed mixed at the end of a volatile week of trading, with the Dow Jones Industrial Average being the only bright spot, as inflation concerns loom over growth names. IHS Markit's data showed U.S. business activity picked up in May amid strong domestic demand, but backlogs of uncompleted work are piling up as manufacturers struggle to find raw materials and labor.