Abstract:
Background Cholesterol is associated with non-small cell lung cancer tumorigenesis and promotes drug resistance of non-small cell lung cancer cell lines, and it is reported that lactate induces an increased intracellular cholesterol level via activated SREBP2 by low pH.
Objective To explore possible regulatory mechanism of cholesterol level by lactate.
Methods The correlation of expression levels between LDHA and cholesterol biosynthesis-related genes in human non-small cell lung cancer from TCGA was analyzed. The cultured human bronchial epithelial BEAS-2B cells and human non-small cell lung cancer H1299 cells were divided into control group (cultured with normal medium) and lactate group (cultured with medium containing lactate). Human non-small cell lung cancer A549 cells were divided into control group, lactate group and hydrochloric acid group (cultured with medium containing hydrochloric acid). The intracellular total cholesterol level was measured using total cholesterol test kit, and mRNA levels of cholesterol biosynthesis-related genes were examined with qPCR. In control and lactate-treated A549 cells, chromatin immunoprecipitation was used to analyze histone lactylation level within the promoters of genes involved in cholesterol biosynthesis.
Results Wilcoxon rank sum test analysis of TCGA data of human non-small cell lung cancer indicated that there was a positive correlation between LDHA expression level and expression levels of cholesterol biosynthesis-related genes including HMGCR, ACAT1, ACAT2, SQLE and FDFT1 (P<0.05). Compared to control group, BEAS-2B, A549 and H1299 cells treated with lactate had an increased intracellular total cholesterol level (P<0.01), and mRNA levels of HMGCR, FDPS, GGPS1 and SQLE were also up-regulated in BEAS-2B and A549 cells treated with lactate (P<0.01). Compared to control group, A549 cells treated with lactate or hydrochloric acid presented an increase in intracellular total cholesterol level (P<0.05) and mRNA levels of HMGCR and FDFT1 (P<0.01). However, the cholesterol level in lactate-treated A549 cells was much higher than that in hydrochloric acid-treated A549 cells (P<0.01). Higher histone lactylation level within HMGCR, SQLE and GGPS1 promoters was observed in lactate-treated A549 cells compared to control A549 cells. In addition, inhibition of LDHA by sodium oxamate reversed lactate-induced total cholesterol in A549 cells (P<0.01).
Conclusion Lactate triggers an increase in human non-small cell lung cancer cells. The possible underlying molecular mechanism may be histone lactylation stimulating expression of cholesterol biosynthesis-related genes, and lactate is also metabolized to generate acetyl coenzyme A to synthesize cholesterol.
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