U.S. stock-index futures signaled a lower open on Wednesday, as Wall Street considered the ADP employment report, which comes ahead of the government's nonfarm payrolls report, out on Friday. 

Automatic Data Processing published its January report on private sector employment, with 175,000 jobs created during the month. Economists polled by Reuters had forecast 180,000 jobs were created during the month, down from 238,000 in December.