It is very important to hand wash underwire Bras. If you wash your underwire bras in a washing machine, not only will you rip the wire out of your bra, it can get stuck in your machine and ruin it as well.
If your lucky enough to not loose your wire, it will move, making the bra fit differently and be very uncomfortable to wear. But what about wash bags you ask.... Well this is still not a good idea as the wire will move with washing this way as well.
Keep your wash bags for your knickers and other lingerie but hand wash your bras.