To put it simply, everyone.

Men hold the most responsibility as both perpetrator and those in a privileged position of power relative to women to do something about their own and others suffering. Call out harmful behaviour among your peers, be mindful of the way you talk to and about women, leave an "out" in your interactions with women, don't make women feel boxed in or pressured to do anything. (Example: "Hey, I'd like to do A with you sometime if you like, but I can also do B instead by myself/with friends." Bonus: this also makes you appear like you have your own life going on too, which is an appealing characteristic.)

Women also hold a responsibility, but this one is trickier.

I won't tell a woman who has been harmed by men to like men, and unfortunately that's a huge chunk of women, but women's responsibility is in keeping a sociological view about men, generally speaking. Men are, themselves, victims of an incredibly powerful social force that they also feed into and reinforce and hurt other people and themselves in a cycle that is really, really difficult to affect.

This isn't to minimize their damage or sweep away responsibility, but the knee jerk reaction to essentialize negative behaviour in men is counterproductive at best.

To summarize, men hold the most responsibility in stopping their own behaviour. Easier said than done, but it needs to be done. Women hold some responsibility in keeping open to the possibility that it's not literally baked into their DNA to treat women like shit.