Houghton Mifflin Harcourt will relocate its headquarters from Boston’s Back Bay to 125 High St. in the Financial District when its lease expires in early 2017.

The publisher will fill 162,000 square feet in the building, which will have 376,000 square feet becoming available this year when PwC moves to 101 Seaport, an office tower under construction on the South Boston waterfront.

The 16-year lease covers the fifth through eighth floors.

“We are seeing lots of positive leasing activity in the Financial District submarket, which is steadily becoming a destination for technology, media, advertising and information tenants, as well as professional, legal and financial services firms,” Samuel Schaefer, managing director of developer Tishman Speyer, said in a statement. “This transaction further demonstrates the diversification of the Financial District, as well as the strength of Boston’s local economy.”

Houghton Mifflin currently occupies 222 East Berkeley St. in Back Bay, part of a 1.3-million-square-foot tower owned by Equity Office Properties that also includes 500 Boylston St. That property recently was placed on the market and is expected to fetch well over $1 billion. The Houghton Mifflin departure is not expected to hurt the sale price because replacement tenants could sign leases for higher rents than Houghton Mifflin was paying, industry sources say.

125 High St. is a three-building, 1.5-million square-foot complex spanning a city block bounded by High, Oliver, Purchase and Pearl streets. 125 High St. recently achieved LEED Gold for Existing Buildings certification under the U.S. Green Building Council’s LEED rating system.

Cushman & Wakefield’s Gil Dailey represented Houghton Mifflin in the transaction.

Tishman Speyer is also expected to break ground later this year on an office tower and condominium development at the Pier 4 site on Northern Avenue in the Seaport District.