Concerns about Greece weigh down stocks

Renewed concerns that Greece will exit the euro weighed the markets down during the midday with the Dow losing 54 points to 17,770. Nasdaq slipped 3 points to 4,740.

On the upside

China Green Agriculture (NYSE: CGA) reported higher second quarter earnings and revenue.

Rising crude oil prices lifted shares of North Atlantic Drilling (NYSE: NADL).

The Organization of Petroleum Exporting Countries expects oil demand to rise in 2015 sending shares of Penn West Petroleum (NYSE: PWE) higher.

On the downside

Regulus Therapeutics (Nasdaq: RGLS) reported that patients experienced relapse in a study evaluating RG-101 to treat hepatitis C virus infection.

J.P. Morgan downgraded Alcoa (NYSE: AA) from an Overweight rating to a Neutral rating.

Investors locked in profits on Twitter (NYSE: TWTR).

In the broad market, advancing issues outpaced decliners by a margin of nearly 5 to 4 on the NYSE and by nearly 10 to 9 on Nasdaq. The broader S&P 500 slipped 2 points to 2052. Bitcoin lost $3 to $218.