WASHINGTON—The Pension Benefit Guaranty Corp. said Thursday that it has taken over and terminated seven underfunded pension plans sponsored by the Chicago Sun-Times.

The PBGC said it took the action because the Chicago-based newspaper publishing company sold substantially all of its assets in bankruptcy proceedings and the private investment group that bought the assets did not assume responsibility for the pension plans.

The Sun-Times filed for bankruptcy reorganization last year. In October 2009, a bankruptcy court approved the sale of substantially all of the Sun-Times assets to STMG Holdings L.L.C.

The plans are 53% funded, with $55.8 million in assets and $106.5 million in liabilities, according to the PBGC. The PBGC said it expects to be responsible for $49.1 million of the $50.7 million funding shortfall.

The seven plans have 2,360 participants.