Diagnostic and prognostic value of the cancer-testis antigen lactate dehydrogenase C4 in breast cancer
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.
Section snippets
Clinical data
Serum samples were collected from 75 BC patients who were admitted to Fujian Cancer Hospital from December 2018 to May 2019, and 120 healthy controls. The BC cases encompassed 24 preliminary diagnosis/preoperative cases, 32 postoperative cases and 19 recurrence cases. All the 75 cases had invasive ductal carcinoma, and were diagnosed by pathological examinations. Collection of all serum samples was approved by the Ethics Committee of Fujian Cancer Hospital (ethical approval certificate: No.
Identification of the isolated vesicles
The purified exosomes were first identified by the transmission electron microscope. As shown in Fig. 1A, the membranous vesicles, 40 to 140 nm in diameter, were observed in eluent. Immunoblotting showed that the exosome marker proteins, CD9 and CD 63, were datable in the purified eluent (Fig. 1B), suggesting that serum-derived exosomes were successfully isolated.
Serum and serum-derived exosome LDHC was an appropriate biomarker for BC
Quantitative RT-PCR indicated that the positive rates of LDHC mRNA in serum and serum-derived exosomes of BC patients were 91.66%
Discussion
CTA is only expressed in the germinal epithelium of the testes and some tumor tissues [3], [4], [5], [6]. LDH-C4, a class of LDH isozyme and a component of the lactate-pyruvic acid transition in carbohydrate metabolism pathways, specifically expressed in sperm and testicular tissue of birds and mammals [5], [7], [10]. As a class of CTA, LDH-C4 is expressed in some malignant tumor cells and translated to zymoprotein with normal biological activity [7], [15], [18]. Recently, studies have reported
Funding
This study was sponsored by the National Natural Science Foundation of China (Grant number: 81802631), Fujian Provincial Health Technology Project (Grant number: 2016-ZQN-17), and Joint Funds for the Innovation of Science and Technology, Fujian province (Grant number: 2017Y9073), and Science and Technology Program of Fujian Province, China (Grant number: 2018Y2003).
CRediT authorship contribution statement
Z. Cui: Conceptualization, Funding acquisition, Writing - original draft. YS. Chen: Investigation, Data curation, Formal analysis. M. Hu: Data curation, Formal analysis, Methodology. Shu. Zhang: Software. L. Kong: Conceptualization, Project administration, Validation. Y. Chen: Conceptualization, Supervision, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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