Galactosylceramide Upregulates the Expression of the BCL2 Gene and Downregulates the Expression of TNFRSF1B and TNFRSF9 Genes, Acting as an Ani-apoptotic Molecule in Breast Cancer Cells

Using a breast cancer (BC) cellular model: MDA-MB-231 cells with blocked synthesis of galacto-sylceramide (GalCer; MDA.Δ.UGT8.4) and MCF7 and T47D cells that over-produced GalCer (MCF7.UGT8 and T47D.UGT8), we found that GalCer increased resistance to doxorubicin, paclitaxel, and cisplatin serving as an anti-apoptotic molecule. These results were supported by a study using murine mammary carcinoma 4T1 cells over-producing GalCer, which were trans-planted into Balb/c mice and were more resistant to doxorubicin therapy than the control. Sub-sequent studies revealed that GalCer specifically downregulated the level of pro-apoptotic TNFRSF1B and TNFRSF9 genes and increased the level of the anti-apoptotic BCL2 gene expres-sion, suggesting that GalCer regulates their expression at the level of transcription. Consistent with this hypothesis, MDA-MB-231 and MCF7.UGT8 cells with high GalCer content showed lower activity of TNFRSF1B and TNFRSF9 promoters than cells lacking GalCer. In contrast, the activity of the BCL2 promoter in MCF7.UGT8 was higher than in MCF7 cells without GalCer. However, no difference in BCL2 promoter activity was observed between MDA-MB-231 cells with high GalCer level and GalCer-negative MDA.Δ.UGT8.4 cells. Instead, we found that GalCer increased the stability of Bcl-2 mRNA. As a candidate protein that simultaneously increases the expression of TNFRSF1B and TNFRSF9 genes and decreases the expression of BCL2 gene and stability of Bcl-2 transcripts is probably p53, its expression was analysed in BC cells containing various amounts of GalCer. In agreement with this hypothesis, BC cells with high GalCer con-tent are characterized by significantly lower expression of p53, and inhibition of p53 using siR-NA resulted in decreased expression of TNFRS1B and TNFRS9 genes and increased expression of BCL2 gene.