ProShares told the SEC it would like to pull its plan to launch four bitcoin ETFs.The move comes a day after Rafferty Asset Management and Exchange Traded Concepts also withdrew applications, citing concerns from regulators.A week ago Direxion Asset Management asked for permission to run ETFs that would offer multiples up or down of bitcoin futures moves.In a letter to the Securities and Exchange Commission, ProShares said it would like to pull its application for four ETFs that would have been tied to bitcoin trading on the futures market.No reason was given for the move, and a ProShares representative said the company would have no comment.