NEW YORK ( TheStreet) -- Stocks closed lower on Thursday, after posting gains earlier in the session, as investors continue to worry over Greece's ongoing debt woes.

The S&P 500 lost 0.30%, the Dow Jones Industrial Average fell 0.42%, or 75 points, and the Nasdaq gave up 0.20%.

After the closing bell, Valeant Pharmaceuticals (VRX) offered to acquire Zoetis (ZTS), an animal-health company, sources told The Wall Street Journal. Valeant rose 0.5% in after hours trading, compared to Zoetis' 1.6% gain. Plus, athletic retailer Nike (NKE) reported earnings per share of 98 cents after the closing bell, beating Thomson Reuters estimates of 83 cents. The stock rose 2.5% following the markets close.

"Concerns around Greece seem to be rising," said Ian Winer, head of equity trading at Wedbush Securities. "But in general it's not a huge move and I wouldn't read too much into it."

Aside from Greece, the Dow Jones Transportation Average fell 0.84% on Thursday, reaching correction territory, falling over 10% since its November 2014 high.

It was a busy day for health stocks. Shares of Humana (HUM) jumped after reports surfaced that Aetna (AET) was close to acquiring the health care giant.

Bloomberg reported Aetna was closing in on an acquisition of Humana and could reach a deal as early as this weekend. Humana shares closed ahead 7% after being halted earlier for volatility.

Meanwhile, hospital operators also rose sharply following the 6-3 Obamacare Supreme Court ruling that determined subsidies should be available in states where health care exchanges weren't created; HCA (HCA) jumped 9%, while Tenet Healthcare (THC) rose 12%, making it the best-performing stock in the S&P 500. Community Health (CYH) added 13%.

"Health care is no longer a defensive sector, it's a growth sector," Mary Ann Bartels, chief investment officer of portfolio solutions at Merrill Lynch Wealth Management, told TheStreet TV. "We have 10,000 baby boomers turning 65 who will need health care going into retirement. [The Supreme Court ruling] is another positive point for the health care sector."

Crude oil slipped below $60 a barrel, settling a $59.66, a 1% drop. 

Greek's leaders and the country's creditors met in Brussels on Thursday. After a three-hour meeting, no deal was reached, according to The Guardian. Greece's latest debt payment is due to the International Monetary Fund on June 30. Greece is reluctant to agree to austerity measures.

"The closer we get to the June 30 deadline it is becoming increasingly apparent that Greece will not be repaying the IMF its 1.5 billion euros on time," said Michael Hewson, chief market analyst at the London-based CMC Markets.

Personal income in the U.S. in May rose 0.5%, according to the Bureau of Economic Analysis. Consumer spending rose 0.9%, the largest jump in some six years.

CenturyLink (CTL) was the worst performing stock in the S&P 500, after analysts at JPMorgan downgraded the stock to "neutral" from "overweight," following the company's analyst day.

Barnes & Noble (BKS)
reported a fiscal fourth-quarter loss of 37 cents a share, compared to estimates of 33 cents. Revenue came in at $1.2 billion, ahead of estimates of $1.18 billion. Shares slipped about 1.5%.

Walt Disney (DIS) closed higher by about 0.60%. The entertainment company will raise its dividend 15% and make semi-annual payments to shareholders, instead of annual ones.

IAC/InterActiveCorp (IACI) announced plans for an initial public offering of its popular dating Web site Match.com. The stock ended Thursday's trading day ahead 5%.

Accenture (ACN) reported earnings per share of $1.30, eclipsing Wall Street's estimates of $1.23. The consulting firm also raised its revenue outlook for the year and expects sales to rise 9% to 10%, compared to a previously reported 8% to 10%. Shares gained 1.75%.

As for Friday, athletic retailer Finish Line (FINL) reports financial results. Analysts expect earnings per share of 25 cents. 

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