U.S. futures slip as Greece continues to weigh

(Reuters) - U.S. stock index futures were lower on Friday, after closing up for the second straight day, as optimism regarding a resolution of the Greek debt crisis faded.

* U.S. stocks climbed on Thursday as retail sales data lifted the outlook for consumer spending and as healthcare shares gained.

* The International Monetary Fund dramatically raised the stakes in Greece's stalled debt talks late on Thursday, announcing that its delegation had left negotiations in Brussels and flown home because of "major differences" with Athens.

* The Producer Price Index for May is expected to have increased 0.4 percent for the month, compared with the 0.4 percent decline in April. The data is expected at 8:30 a.m. ET.

* The University of Michigan's preliminary June reading on the overall index on consumer sentiment is expected to have risen to 91.5 from 90.7. That data is expected at 10:00 a.m. ET.

* The Fed has said it will raise rates only when it sees a rebound in the economy, which came to a standstill in the first quarter.

* Economists and top Wall Street banks expect the Fed to raise rates in September, in what could be the central bank's first hike in almost a decade and turn the direction of the flow of easy money that has driven world stocks and bond prices to record highs in recent years.

* Twitter Inc's shares were up 4.6 percent at $37.51 in premarket trading, a day after Chief Executive Officer Dick Costolo abruptly announced he was stepping down.

* T-Mobile jumped 6.7 percent to $40.69 after sources said Dish Network was in talks to hire banks that would provide between $10 billion and $15 billion in debt to finance the cash portion of its bid for the company.

Futures snapshot at 7:29 a.m. ET:

* S&P 500 e-minis were down 6.75 points, or 0.32 percent, with 79,986 contracts traded.

* Nasdaq 100 e-minis were down 18 points, or 0.4 percent, on volume of 7,246 contracts.

* Dow e-minis <1YMc1> were down 49 points, or 0.27 percent, with 6,984 contracts changing hands.

(Reporting by Tanya Agrawal)