Background: We investigated the effects of 1,25(OH)2D3 and selected analogs on canine squamous carcinoma cells (SCC 2/88) and tested whether these compounds could effectively decrease proliferation, induce differentiation, and inhibit PTHrP production and PTHrP mRNA expression.
Materials and methods: SCC 2/88 cells were cultured and treated with three substrates. The media were collected for PTHrP immunoradiometric assay. The cells were analyzed for DNA concentration and PTHrP mRNA expression by Northern blot analysis, involucrin by Western blot analysis and 1,25(OH)2D3-receptor (VDR) and PTHrP by immunohistochemistry.
Results: The SCC 2/88 cells were stained positively for VDR and PTHrP by immunohistochemistry. 1,25(OH)2D3 and its analogs inhibited cell growth and stimulated differentiation in a dose-dependent manner. All three substrate-treated groups had significantly increased PTHrP secretion at 10(-7) M. Cells treated with 1,25(OH)2D3 at 10(-7) M had 2- to 4-fold increased PTHrP mRNA expression at 12 and 24 hours compared to the vehicle-treated controL PTHrP mRNA in cells treated with TGF-beta (1.5 ng/ml) was increased 7- to 17-fold at 6, 12 and 24 hours compared to the vehicle-treated controL PTHrP mRNA expression was reduced by 0.5- to 2-fold in cells treated with 1,25(OH)2D3 at 10(-7) M and TGF-beta (1.5 ng/ml) together compared to cells treated with TGF-beta alone.
Conclusion: 1,25(OH)2D3, EB1089, and analog V inhibited SCC 2/88 growth and induced differentiation in a dose-dependent manner, but did not inhibit PTHrP production. 1,25(OH)2D3 treatment led to increased PTHrP mRNA expression and reduced the stimulatory effect of TGF-beta on PTHrP mRNA expression in SCC 2/88 cells.