AKo, two villains

[guaranteedBluff]

Party Poker No-Limit Hold'em, $.5/1 BB (9 handed) internettexasholdem.com

MP1 ($109.45)
Hero ($120.05)
MP3 ($114.05)
CO ($215)
Button ($43.65)
SB ($137.70)
BB ($37.40)
UTG ($111.40)
UTG+1 ($161.80)

Preflop: Hero is MP2 with A[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/diamond.gif[/img]. SB posts a blind of $0.50.
3 folds, Hero raises to $4, MP3 calls $4, CO calls $4, Button calls $4, SB (poster) calls $3.50,1 fold.

Flop: ($21) A[img]/images/graemlins/heart.gif[/img], 2[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/diamond.gif[/img] (5 players)
SB checks, Hero bets $15, MP3 calls $15, CO folds, Button raises to $39.65 (All-In), SB folds, Hero ???

MP3 is 33/7/passive. Has called down a few hands and showed down with a mediocre kicker.

Button - no reads, but wouldn't be surprised if this shortstack stack is a complete bluff.

What's your line? PF, flop, etc..