Treating multiple subdimensions as a unidimensional variable in hypotheses testing

#1
Hi! I would be very grateful if someone could clear up the following question for me: I'm using SPSS macro Process (Hayes, 2018) to test my model. My dependent variable has three subdimensions. The PROCESS allows to test a single dependent variable at a time. I am confused if I can treat those subdimensions as a unidimensional variable to test my hypotheses.