Drug sensitivity and sphingolipid metabolism in CLL

Increased ceramide production sensitizes breast cancer cell response to chemotherapy

BACKGROUND

Advanced breast cancer remains clinically challenging due to its resistance to chemotherapy. To understand the underlying mechanisms of resistance and identify drugable target, the involvement of ceramide metabolism is investigated.

METHODS

Ceramide levels in breast cancer tissues derived from 30 patients with stage IV breast cancer before and after chemotherapy were analyzed using liquid chromatography mass spectrometry. mRNA and protein levels of ceramide enzymes were examined using western blot and QRT-PCR. The effects of ceramide analog were investigated using cellular assays and xenograft tumor model.

RESULTS

The results demonstrated that pro-apoptotic ceramide was significantly lower in all patients after chemotherapy, suggesting that downregulation of ceramide is a common feature of breast cancer patients in response to chemotherapy. Molecular characteristics analysis of ceramide indicated C16:0 as the predominant sphingolipid regulated by chemotherapy in breast cancer patients. Mechanistically, ceramide levels were suppressed by chemotherapy via increasing mRNA and protein levels of UDP-glucose ceramide glucosyltransferase (UGCG). Importantly, inhibition of UGCG using siRNA or upregulation of cellular ceramide levels using C2 ceramide alone inhibited proliferation and induced apoptosis of breast cancer cells, and enhanced the inhibitory effects of chemotherapeutic drugs in vitro and in vivo.

CONCLUSIONS

This study clearly demonstrated that the decreased ceramide production via up-regulating UGCG was involved in the resistance of breast cancer cells to chemotherapy. Stimulating ceramide or decreasing UGCG can potentially be useful for breast cancer treatment.

Recent insights into the molecular pathophysiology of lipid droplet formation in hepatocytes

Triacyglycerols are a major energy reserve of the body and are normally stored in adipose tissue as lipid droplets (LDs). The liver, however, stores energy as glycogen and digested triglycerides in the form of fatty acids. In stressed condition such as obesity, imbalanced nutrition and drug induced liver injury hepatocytes accumulate excess lipids in the form of LDs whose prolonged storage leads to disease conditions most notably non-alcoholic fatty liver disease (NAFLD). Fatty liver disease has become a major health burden with more than 90% of obese, nearly 70% of overweight and about 25% of normal weight patients being affected. Notably, research in recent years has shown LD as highly dynamic organelles for maintaining lipid homeostasis through fat storage, protein sorting and other molecular events studied in adipocytes and other cells of living organisms. This review focuses on the molecular events of LD formation in hepatocytes and the importance of cross talk between different cell types and their signalling in NAFLD as to provide a perspective on molecular mechanisms as well as possibilities for different therapeutic intervention strategies.