A number of prestigious people from AI and other fields have signed the open letter, including Stuart Russell, Peter Norvig, Eric Horvitz, Ilya Sutskever, several DeepMind folks, Murray Shanahan, Erik Brynjolfsson, Margaret Boden, Martin Rees, Nick Bostrom, Elon Musk, Stephen Hawking, and others. I'd edit that into the OP.
Also, it's worth noting that the research priorities document cites a number of MIRI's papers.
The Future of Life Institute has published their document Research priorities for robust and beneficial artificial intelligence and written an open letter for people to sign indicating their support.