Role of CPT1C in breast cancer development and chemoresistance

Abstract

Carnitine palmitoyl transferase 1 (CPT1) are enzymes that catalyze the conversion of long-chain acyl-CoA to acyl-carnitines, to transport long-chain fatty acids across intracellular membranes. CPT1C isoform is highly different respect the other CPT1 isoforms. It is located in the endoplasmic reticulum of cells, rather than in mitochondria, and it does not have catalytic activity. An animal model deficient in CPT1C and the interactions described between CPT1C and other proteins have related CPT1C with major functions as cognition, motor function, and energy homeostasis.

In 2011, it was first showed that CPT1C was overexpressed in many human cancers conferring them higher cell survival and tumor growth under conditions of metabolic stress, like hypoxia or glucose deprivation. Several publications have confirmed the crucial role of CPT1C in cancer development.

The aim of our work was to study whether CPT1C promoted proliferation, migration, invasion and chemotherapy resistance in breast cancer cells, using triple-negative cancer MDA-MB-231 cells as a model. Several assays showed that CPT1C silencing increases cell proliferation and cell invasion; however, it does not impair cell migration. Interestingly, CPT1C silencing also increases cell survival to doxorubicin or paclitaxel treatment, in several breast cancer cell lines. This effect was explained by a reduced drug influx, as demonstrated in doxorubicin uptake assays in CPT1C-silenced MDA-MB-231 cells.

Doxorubicin is a drug that enter cell mainly through passive diffusion and this drug transport is highly dependent on plasma membrane lipid composition. For this reason, we performed a lipid analysis of plasma membrane enriched fractions of MDA-MB-231 cells by liquid chromatography-high resolution mass spectrometry (LC-HRMS). We confirmed that, under CPT1C silencing, there is a lipid plasma membrane remodeling giving rise a more rigid membrane and thus, less permeable to drugs.

All these results match with the Kaplan-Meier Plotter and ROC plotter analysis that correlates lower expression of CPT1C in HER2-positive and triple-negative human breast tumors with worse prognosis and lower pathological complete response, pointing out CPT1C as a novel tumor prognostic marker in the treatment of breast cancer.