Twitter closed mildly higher, losing earlier gains of about 3 percent. The stock is in focus after spiking 9 percent in after-hours trade following the late Thursday afternoon announcement that CEO Dick Costolo would step down next month. The news comes after investor calls for a leadership shakeup following a sluggish run for Twitter stock as the tech company struggles to grow revenue and expand its user base.
Incoming CEO Jack Dorsey said on CNBC's "Squawk On The Street" that he will maintain Twitter's strategy regardless of criticism.
The standoff between Greece and its creditors worsened on Thursday after the International Monetary Fund walked out on talks with Athens, citing "major differences" over how to save the country from bankruptcy. The news pressured stocks, with European and U.S. equities closing with mild gains.
Peter Cardillo, chief market economist at Rockwell Global Capital, said he doesn't "see much panic in the market" and the IMF's announcement was "probably more of a pressure tactic."
"With the markets focusing on Greece and a little bit of uptik in yields, this morning, we're probably looking at a market that's going to be trading sideways," he said, noting some nervousness ahead of next week, with the Federal Open Market Committee releasing its highly-anticipated June statement and quarterly options expiration on Friday.
Investors will scrutinize the statement for clues on the timing of a short-term interest rate hike. Consensus is for the U.S. central bank to begin tightening in September.
European stocks closed lower on Friday, with the German DAX 1.2 percent lower after falling more than 2 percent. The ATHEX Composite ended nearly 6 percent lower.
Senior European Union officials have formally discussed for the first time a possible Greek debt default as negotiations between Athens and its creditors have stalled ahead of an end-month repayment deadline, several officials told Reuters.
Still, analysts remain confident Greece will remain in the euro zone.
"We would expect there would be some type of resolution that will allow Greece not to default ... likely to be a more short-term solution, buying time," said Eric Wiegand, senior portfolio manager with U.S. Bank's private client reserve. "We do think investors should be aware things are likely to increase—more volatility not only around headlines surrounding Greece but economic data. We get a central bank meeting next week."
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In economic reports out Friday, the Producer Price Index increased 0.5 percent for May, topping expectations for 0.4 percent. The gain was the largest since May 2012. The core PPI figure of ex-food, energy and trade services fell 0.1 percent for the month.
The preliminary Michigan consumer sentiment posted 94.6 for June, an increase from May's final read of 90.7.
"The focus for the U.S. equity market is the turnaround in the U.S. economy on the positive side and the Greek drama on the negative side," said Krishna Memani, chief investment officer at Oppenheimer Funds. "The sentiment for the U.S. market is extremely negative. If we get any rate stability and economic improvement (the trend will be) higher rather than lower."
Bond markets were calmer on Friday. The U.S. 10-year Treasury yield traded near 2.39 percent on Friday, near Thursday's closing level. The benchmark yield hit 2.5 percent level for the first time since Oct. 1 on Thursday, following the 10-year German bund yield's largest one-day drop in two years.
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The U.S. dollar traded flat against major world currencies with the euro creeping towards $1.13 on encouraging headlines out of Greece. Earlier, the euro dipped to near $1.12 after comments from German Chancellor Angela Markel that a "too strong" euro made reforms for countries such as Spain and Portugal difficult.