Diagnostic and prognostic value of the cancer-testis antigen lactate dehydrogenase C4 in breast cancer

Highlights

• LDHC mRNA and protein are up-regulated in BC.

• Serum or exosomal LDHC is a powerful indicator in the management of patients with BC.

• LDH-C4 serves as a promising prognostic biomarker for BC.

Abstract

Background

Lactate dehydrogenase C4 (LDH-C4) as a cancer/testis antigen (CTA) is abnormally expressed in some malignant tumors. However, the expression and clinical significance of LDH-C4 in breast cancer (BC) has not been characterized.

Methods

We determined LDHC mRNA expression in serum and serum-derived exosomes of BC patients by quantitative RT-PCR. We also evaluated the protein expression of LDH-C4 in BC tissues using high-throughput tissue microarray analysis and immunohistochemistry.

Results

Our results showed high mRNA expression level of LDHC in serum and serum-derived exosomes of BC patients. The LDHC level in serum and exosomes could distinguish BC cases from healthy individuals based on their AUCs of 0.9587 and 0.9464, respectively. Besides, the LDHC level in exosomes of BC patients associated with tumor size, and positively correlated with HER2 and Ki-67 expressions (all with P < 0.05). Serum and exosomal level of LDHC negatively correlated with medical treatment and positively with the recurrence of BC. Survival analysis showed that LDH-C4 expression negatively correlated with BC prognosis.

Conclusion

Serum and exosomal LDHC may be an effective indicator for the diagnosis, efficacy evaluation, and monitoring the recurrence of BC. LDH-C4 may act as a biomarker that predicts BC prognosis.

Introduction

BC is one of the most common malignant tumors mainly appearing in females worldwide [1]. According to the latest cancer epidemiology in China, BC has been the fourth-most fatal cancer that mostly occurs in female patients with malignancy [2]. Early diagnosis, timely treatment and accurate prognosis are crucial determining factors for BC survival rate, which requires identification of novel tumor markers for the disease as the first imperative for researchers.

CTA, expressed only in the germinal epithelium of the testes and some tumor tissues, may be a marker for tumor diagnosis and immunotherapy [3], [4], [5], [6]. LDH-C4 protein (also known as LDHX), encoded by the LDHC gene, is expressed merely in the testes and tumors [7], [8]. The human LDHC gene is located on chromosome 11p15.3–15.5. The full-length mRNA of LDHC is 1179 bp. The LDHC gene has two transcripts with an open reading frame containing 999 base pairs. The LDHC gene encodes a C subunit with a relative molecular mass of 35 kDa. Four identical C subunits undergo polyhomologation to form the catalytically active tetrameric protein, LDH-C4 zymoprotein [6]. As a CTA molecule, the expression of LDH-C4 is specific to mature testes and sperm of healthy males [7], [8]. Specifically, LDH-C4, as an important molecular index for maturation of male germ cells and assessment of fertility, plays a critical role in sperm energy metabolism [7], [9], [10].

Splice variants of LDHC have been observed in the testes of various mammals according to recent researches, often accompanied by mutations such as deletions of exons 5, 4, and 6 [11]. LDH-C4 mRNA and protein are expressed in the myocardium, liver, lung, kidney, brain, skeletal muscle and other tissues of plateau pikas [12], [13]. The expression of LDH-C4 in somatic cells of plateau pikas suggests that it may correlate with energy metabolism. However, few studies have shown solicitous attention on its role in malignant tumors. One study reports that LDHC mRNA is expressed in many types of tumors, and the positive expression rates of its spliceosome are 47% in lung cancer, 44% in melanoma, 35% in BC, and 15% in colon cancer [14]. It can be hypothesized that LDHC may be involved in the onset and development of these cancers. Grunwald et al. present a 25% increase in the mRNA expression of LDHC in non-small-cell lung carcinoma (NSCLC) tissue. Furthermore, the mRNA expression of LDHC in NSCLC was comparable to that in adenocarcinoma and squamous cell carcinoma [15]. The mRNA and protein expressions of LDHC significantly increase in renal cell carcinoma, and LDHC-positive patients usually associates with worse outcomes [16].

In our previous work, we have developed a novel histochemical staining method for the detection of LDH-C4 activity [17], observing abnormal expression of LDH-C4 in MDA-MB-231 cells [18]. The LDH-C4-specific inhibitor, N-propyl oxamate, can reduce the invasion and migration of MDA-MB-231 cells [18]. In the present study, we investigated serum and exosomal level of LDHC mRNA, quantified the protein expression of LDH-C4 in BC tissues using high-throughput tissue microarray analysis and immunohistochemistry, and evaluated the correlation of LDH-C4 expression with clinical pathological characteristics and BC prognosis.