The U.S. stock index futures point to a slightly lower open Wednesday as investors remained cautious waiting for Federal Reserve Chairman Ben Bernanke to announce monetary easing measures at the Jackson Hole symposium later this week.

Futures on the Dow Jones Industrial Average were down 0.09 percent, futures on the Standard & Poor's 500 index were down 0.06 percent and those on the Nasdaq 100 index were down 0.02 percent.

The U.S. Bureau of Economic Analysis will report Wednesday the second estimate of the second quarter gross domestic product (GDP), which measures the annualized change in the inflation-adjusted value of all goods and services produced by the economy. The U.S. economy is expected to have expanded at 1.7 percent in the second quarter, but that is down from the 1.9 percent rise of the first quarter. The first estimate of the second quarter GDP reported last month showed that the economy expanded at 1.5 percent.

The National Association of Realtors' (NAR) Pending Home Sales Report, which measures the change in the number of homes under contract to be sold but still awaiting the closing transaction excluding new construction, will also be reported Wednesday. It is expected that the report would show a 1 percent rise in July, up from the 1.4 percent decline in June.

On Tuesday, the U.S. markets were mixed as investors remained cautious even after receiving better- than-expected housing data. The S&P/Case-Shiller House Price Index, which measures the change in the selling price of single-family homes in 20 metropolitan areas, reported Tuesday a rise of 0.5 percent in June compared to that in the same month last year.

The Dow Jones Industrial Average fell 0.17 percent, the S&P 500 Index was down 0.08 percent and the Nasdaq Composite Index advanced 0.13 percent.

Major European indices were in red as market participants felt uncertainty with policymakers not announcing bold stimulus measures to revive the weakening euro zone economy. European Central Bank President Mario Draghi has cancelled his speech at Jackson Hole this Saturday. The news has come as a disappointment to investors who expected Draghi would make the ECB's plans clearer. London's FTSE 100 was down 17.85 points, Germany's DAX 30 Index fell 2.47 points and France's CAC 40 declined 1 point.

Asian stocks were mixed following the global cues.