BERLIN, Feb 10 (Reuters) - German prosecutors have opened preliminary proceedings against Gregor Gysi, one of the Left party's key election campaign figures, over allegations he lied about links with the former East German secret police, the politician said on Sunday. Gysi, who leads the Left party's parliamentary group, has repeatedly faced allegations in the past two decades that as a lawyer in former East Germany he passed information on clients - some of them known dissidents - to the Stasi secret police.