From J. Edgar Hoover Goes to the Movies: The FBI and the Origins of Hollywood's Cold War, by John Sbardellati:

Jack Warner, eager to erase the public memory of “Mission to Moscow,” announced to the committee and the press his studio’s plans for an anti-Communist feature tentatively titled “Up until Now.” His company’s press statement affirmed that “backslid Americans, as well as outside enemies of our free institutions, will be exposed in this story of a Boston family. Here at Warner Brothers we have no room for backslid Americans and wishy-washy concepts of Americanism.” The film was to star Claude Rains as the troubled father of a wayward son, played by Ronald Reagan, who would be lured into the Communist Party. Warner, however, dropped the project later in the year, believing that the public had had enough of Hollywood politics in the wake of HUAC’s fall hearings.

Not an April Fools' joke.

“I have not, nor have ever been, a member of the Commu ... Well, except for that one picture. I remember it well. Jack Warner came to me and said, 'Ronnie, you look like the kind of son of a gun that would ...'”