TOKYO, June 25 (Reuters) - Toshiba Corp"s (6502.T) board appointed CEO Satoshi Tsunakawa as interim board chairman on Friday after shareholders displeased with corporate governance at the Japanese conglomerate"s ousted Chairman Osamu Nagayama. Nagayama"s dismissal comes after an independent investigation he opposed establishing this month accused Toshiba of colluding with Japan"s trade ministry to pressure foreign shareholders to back management board nominations.