By Luciana Lopez NEW YORK (Reuters) – Jana Partners LLC built a major stake in Juniper Networks in the fourth quarter, according to a regulatory filing on Friday, making it another shareholder activist to invest in the networking-gear company and urge cost cutting. The bet on Juniper Networks, which by late afternoon was at $27.38, down 0.35 percent, has translated into hefty profits if Jana still holds the stake: Juniper stock has jumped 21 percent so far this year. Janas 13.4 million-share stake in Juniper means the activist investor owns about 2.65 percent of the company. The hedge fund has been talking to Juniper management to try to unlock shareholder value and has cited management compensation as an area of reform, according a letter to investors reported on by Reuters.