Taken together, PGD2 activates the PTGDR2 downstream signaling cascade by inducing the expression of its receptor PTGDR2 and competes with ATG4B for binding RNF5 via PTGDR2, which reduces the binding of RNF5 to ATG4B, promotes ATG4B protein expression, and further activates autophagy to promote autophagic apoptosis in tumor cells. The gene discussed is ATG4B; the disease is neoplasm.