European shares opened lower on Wednesday after the resignation of Donald Trump's economic adviser Gary Cohn, seen as a bulwark against protectionist forces within the U.S. government.

The pan-European STOXX 600 index fell 0.5 percent in early dealing and Wall Street futures traded in negative territory.

"Gary Cohn's departure rattled markets and equity markets look set to fall on the open. Stocks have declined overnight in Asia and it's looking like it will be red today on the open", Neil Wilson, a Senior Market Analyst at ETX Capital told his clients in a morning note.

Most European markets and sectors were down, with Germany's DAX .GDAXI falling the most, down 0.7 percent.

British plane engine maker Rolls-Royce (RR.L) was the best Stoxx index performer, surging 8.5 percent after saying it remained on track to meet its financial goals for 2020.

Second came Smurfit Kappa (SKG.I), after U.S. peer International Paper (IP.N) revealed the takeover offer it made for Europe's largest paper packaging producer was worth 8 billion euros.

The advertising sector took a hit after the Financial Times said P&G (PG.N) would cut agency spending by 1.25 billion dollars over three years. France's Publicis (PUBP.PA) and Britain's WPP (WPP.L) fell 1.9 percent and 1.6 percent respectively.