UPDATE 2-Icahn joins Amylin suit, Green resigns from board

(Recasts; adds details of lawsuit, nominees, share price)

LOS ANGELES, April 9 (Reuters) - Billionaire investor Carl Icahn on Thursday joined a lawsuit against Amylin Pharmaceuticals Inc (AMLN.O) seeking to invalidate debt acceleration provisions that would be triggered in the event of a change in control of the company's board.

Amylin, which has become the object of a proxy fight, also said on Thursday that Howard Greene, its former chief executive, resigned from the company's board following a decision not to nominate him for reelection.

The company said in a regulatory filing that Greene disagreed with the board's decision to limit the number of former CEOs who are directors.

Icahn and affiliates this week filed preliminary proxy material in an effort to elect five of their own nominees to the company's board and said in filing on Thursday that it had joined a class action lawsuit filed last month by the San Antonio Fire & Police Pension Fund.

The actions follow last week's proxy filing by Eastbourne Capital management naming five nominees it hopes to have elected to Amylin's board, setting up a three-way proxy battle for control of the company, which makes the diabetes drug Byetta.

The shareholder suit seeks to disable a "poison put," structured to protect bondholders in the event of a takeover by a company with a lower credit rating.

"Many shareholders expressed an interest in having more commercial and operational expertise in the biopharmaceutical industry on the board," Amylin said in a regulatory filing on Thursday.

The company said two of its directors who are former CEOs, including Greene, were not nominated for reelection.