AKo with a large raise in front

Pacific $5.50 NL, 10 players, blinds 10/20

Stacks:
MP1: 400
MP2: 30
MP3: 760
Hero: 870
Button: 730
SB: 720
BB: 1157
UTG: 720
UTG+1: 1513
UTG+2: 1100

Pre-flop: Hero is CO with A[img]/images/graemlins/diamond.gif[/img] K[img]/images/graemlins/club.gif[/img]
UTG calls, UTG+1 calls, 1 fold, MP1 raises to 400 (allin), 2 folds, Hero??

Results, if you'd like to see them below in white:
<font color="white">Hero raises to 870 (allin), 2 folds, BB calls, 2 folds
Flop: J of spades T of spades K of diamonds
Turn: 8 of spades
River: 2 of hearts
BB shows KK and takes the pot</font>