U.S. stocks down on Greek debt crisis jitters

Creditors demanded sweeping changes to Greek Prime Minister Alexis Tsipras' tax and reforms proposals, adding fresh uncertainty to talks aimed at unlocking aid to avert a debt default next week. Tsipras is scheduled to meet the heads of the European Central Bank, the International Monetary Fund and the European Commission in Brussels before a meeting of euro zone finance ministers at 1300 p.m. ET. "The U.S. market is taking some signals from the weakness in Europe," said John Cana