In a significant shake up, Penguin Random House, the largest publishing house in the United States, announced on Monday that the publishers of two of its most prestigious literary imprints had been let go.

The departure of Reagan Arthur, the publisher of Alfred A. Knopf, and Lisa Lucas, the publisher of Pantheon and Schocken, likely came as a surprise to many in the company — including, it seemed, to Lucas.

Lucas posted on X, formerly called Twitter, that she had learned of her dismissal at 9:30 a.m. on Monday morning. “I have some regrets about spending the weekend working,” she wrote.

In a memo to employees, Maya Mavjee, the president and publisher of Knopf Doubleday, acknowledged the news would likely be unsettling to many, but noted that restructuring the imprints was “necessary for our future growth.”

Mavjee said in the memo that Pantheon’s editorial department will now report to Doubleday, while Knopf will be led by Jordan Pavlin, the editor in chief of Knopf, who will become its publisher, taking on two roles. Pavlin has edited best-selling and award-winning authors including Tommy Orange, Yaa Gyasi and Maggie O’Farrell.

A person in publishing familiar with the decision, and who requested anonymity in order to share details about the restructuring process, said the departures were part of a cost-saving measure. No publisher will replace Lucas at Pantheon, the person said.

The departure of two prominent publishers comes at a moment when Penguin Random House and other big publishing houses are facing financial challenges, with rising supply chain costs and sluggish print sales. Publishers’ sales were flat in the first quarter of 2024, according to a recent report from the Association of American Publishers.

The last two years have been an especially turbulent time at Penguin Random House.

The company has struggled to maintain its dominance in the industry after its bid to buy a rival, Simon & Schuster, was blocked on antitrust grounds, a loss that cost the company a $200 million termination fee. In the aftermath, Markus Dohle, then the chief executive of Penguin Random House, resigned, followed soon after by its U.S. chief executive, Madeline McIntosh.

Its new chief executive, Nihar Malaviya, has moved to cut costs by downsizing and restructuring, and to grow by acquiring smaller publishing companies. Last year, the company offered voluntary buyouts for longtime employees, and laid off about 60 people.

Lucas and Arthur were both splashy hires brought to the company in recent years. Lucas, the first Black publisher at Pantheon in its 80-year history, was hired in 2020 from the National Book Foundation, where she was the organization’s executive director. In her time at Penguin Random House, she published titles including “Chain-Gang All Stars,” by Nana Kwame Adjei-Brenyah, which was a National Book Award finalist, and signed a two-book deal with LeVar Burton.

Arthur, who had been publisher at the imprint Little, Brown, took over as publisher of Knopf in 2020, shortly after the death of Sonny Mehta, who led the imprint for more than three decades. At Knopf, she oversaw the publication of Cormac McCarthy’s final two novels and the enormous best seller “Tomorrow, and Tomorrow, and Tomorrow” by Gabrielle Zevin, and personally edited best sellers including Bono’s memoir, “Surrender,” and “Lessons,” a novel by Ian McEwan.

“It was an honor to get to finally, briefly work in publishing!!” Lucas wrote on X Monday afternoon. “As for what’s next: Who knows! Free agent! I suppose I’ll think about that tomorrow?”