The North American head of JPMorgan Chase & Co's (JPM) troubled Chief Investment Office, Irene Tse, is leaving the company, an internal memo said on Monday.

Tse told the firm she was resigning to focus on "entrepreneurial ventures," according to the memo from Chief Operating Officer Matt Zames.

Tse had been working for the past several months on JPMorgan's overhaul of the CIO, the memo said.

Tse's European counterpart, Achilles Macris, oversaw the desk where trader Bruno Iksil, known as the "London Whale," built up derivatives positions that have cost the bank at least $5.8 billion in losses this year.