Up-regulations of melatonin receptors in cancer cells lead to inhibition of some protein kinases (PKA, protein kinase A; PKC, protein kinase C; MAPK, mitogen-activated protein kinase), decrease the phosphorylation of transcription factors, i.e., CREB (cAMP response element-binding) and reduce the expression of genes associated with the process of proliferation [25,45]. The gene discussed is WEE1; the disease is cancer.