The regulation of parathyroid hormone-related protein expression by colchicine, vinblastine, nocodazole, taxol, transforming growth factor-beta1 (TGFbeta1), and epidermal growth factor (EGF) was investigated in a canine squamous carcinoma cell line (SCC 2/88 cells). SCC 2/88 cells were stably transfected with a human P2/P3 PTHrP promoter-luciferase reporter gene construct and gene expression was measured after chemical treatments. The greatest increase in reporter gene expression was observed after colchicine treatment and small increases occurred after treatment with vinblastine, taxol, TGFbeta1, or EGF. Nocodazole had no significant effect on reporter gene expression. Colchicine also increased PTHrP steady state mRNA expression and PTHrP secretion by SCC 2/88 cells. These results demonstrated that PTHrP production was increased in SCC 2/88 cells by colchicine and suggested that factors or events during mitosis are capable of stimulating PTHrP production. An increase in PTHrP production during mitosis of malignant epithelial cells may be important in the pathogenesis of humoral hypercalcemia of malignancy.