You can only send messages by keyword value, so you have to do this:
from wx.lib.pubsub import pub
...
wx.CallAfter(pub.sendMessage, 'Update', arg1 = ListA, arg2 = ListB)
The arg1 and arg2 must be the same as the listener arguments (so all listeners of given topic ('Update'), and all senders for that topic, must use the same argument names; but the order does not matter, thanks to python's keyword arguments).
Note: the above assumes you are using a fairly recent version of pubsub, with pubsub's default messaging protocol, rather than v1 or arg1. Try printing pub.VERSION_STR or pubsub.VERSION (the latter is in very latest only, wxpython phoenix, not likely the one you are using). Also, if there is a from wx.lib.pubsub import setupv1
or from wx.lib.pubsub import setuparg1
then you are using the old pubsub, which only accepts one message data, but arg name not needed (this could also explain your problem).