Lactate dehydrogenase-B is silenced by promoter methylation in a high frequency of human breast cancers.

Abstract

OBJECTIVE:

Under normoxia, non-malignant cells rely on oxidative phosphorylation for their ATP production, whereas cancer cells rely on Glycolysis; a phenomenon known as the Warburg effect. We aimed to elucidate the mechanisms contributing to the Warburg effect in human breast cancer.

EXPERIMENTAL DESIGN:

Lactate Dehydrogenase (LDH) isoenzymes were profiled using zymography. LDH-B subunit expression was assessed by reverse transcription PCR in cells, and by Immunohistochemistry in breast tissues. LDH-B promoter methylation was assessed by sequencing bisulfite modified DNA.

RESULTS:

Absent or decreased expression of LDH isoenzymes 1-4, were seen in T-47D and MCF7 cells. Absence of LDH-B mRNA was seen in T-47D cells, and its expression was restored following treatment with the demethylating agent 5'Azacytadine. LDH-B promoter methylation was identified in T-47D and MCF7 cells, and in 25/25 cases of breast cancer tissues, but not in 5/5 cases of normal breast tissues. Absent immuno-expression of LDH-B protein (<10% cells stained), was seen in 23/26 (88%) breast cancer cases, and in 4/8 cases of adjacent ductal carcinoma in situ lesions. Exposure of breast cancer cells to hypoxia (1% O(2)), for 48 hours resulted in significant increases in lactate levels in both MCF7 (14.0 fold, p = 0.002), and T-47D cells (2.9 fold, p = 0.009), but not in MDA-MB-436 (-0.9 fold, p = 0.229), or MCF10AT (1.2 fold, p = 0.09) cells.

CONCLUSIONS:

Loss of LDH-B expression is an early and frequent event in human breast cancer occurring due to promoter methylation, and is likely to contribute to an enhanced glycolysis of cancer cells under hypoxia.

• Authors: Nicola J Brown, Sue E Higham, Branko Perunovic, Mohammad Arafa, Sabapathy Balasubramanian, Ishtiaq Rehman
• Journal: PloS one (PLoS One) Vol. 8 Issue 2 Pg. e57697 ( 2013) ISSN: 1932-6203 [Electronic] United States
• PMID: 23437403 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antimetabolites, Antineoplastic
• Isoenzymes
• Neoplasm Proteins
• L-Lactate Dehydrogenase
• lactate dehydrogenase 1
• Azacitidine

Topics

• Adult
• Aged
• Aged, 80 and over
• Antimetabolites, Antineoplastic (pharmacology)
• Azacitidine (pharmacology)
• Breast Neoplasms (enzymology, genetics, pathology)
• Carcinoma, Ductal (enzymology, genetics, pathology)
• Case-Control Studies
• Cell Line, Tumor
• DNA Methylation
• Female
• Gene Expression Regulation, Neoplastic (drug effects)
• Gene Silencing
• Glycolysis (genetics)
• Humans
• Hypoxia (enzymology, genetics, pathology)
• Isoenzymes (genetics, metabolism)
• L-Lactate Dehydrogenase (genetics, metabolism)
• Middle Aged
• Neoplasm Proteins (genetics, metabolism)
• Promoter Regions, Genetic
• Sequence Analysis, DNA