John Cena's putting LOTS of money where his mouth is ... donating $500,000 to first responders helping to battle the California wildfires.
"Right now, California is in dire straits," the WWE superstar said in a video ... "It is burning. It is under siege from massive wildfires statewide."
And, as fate would have it, Cena also happens to be promoting his new movie, "Playing With Fire" -- a comedy about firefighters which opens next month.
Cena says shooting the movie has given him an even greater appreciation for people on the front lines battling the blazes .