Hero calls. Given your discount and the play so far, nothing suggests button has a hand so good that you shouldn't call getting a likely 5-1.

With the right kind of read you could 3-bet, but being out of position means you'd probably rather just see the flop first. The situation where I would 3-bet is where MP is very loose and fishy, and you know button is capable of isolating with a range that includes a fair number of hands worse than K8s. Then you get MP to put in two more bets, and may induce an incorrect fold from button when you have k-high showdown value against MP.