Potential Role Of Monocarboxylate Transporter4(MCT4) In Oral Squamous Cell Carcinoma

Background:Oral squamous cell carcinoma (OSCC) is the sixth most common malignant cancer worldwide. OSCC is characterized by severe progression, partnered with a high potential for both nodal metastasis and locoregional invasion. It has been reported that nodal and distant metastasis in head squamous cell carcinoma is associated with high tumor lactate concentration. MCT4is a cell membrane transporter of lactate, which is very important for the acid-resistant phenotype of cancer cell. Recent studies have shown that MCT4is over-expressed in various types of cancer, however, its role in OSCC has not been fully demonstrated.Objective1、To investigate MCT4expression in OSCC patients and cell lines and to assess the correlation of MCT4level with patients’clinicopathological characteristics and prognosis;2、To explore the function of MCT4in OSCC cell lines;3、To investigate the underlying molecular mechanisms of MCT4in mediating the effects on proliferation, migration and invasion.Methods1、Immunohistochemical staining was used to investigate the expression of MCT4in99OSCC samples. The correlation of the MCT4level with patients’ clinicopathological parameters and prognosis was analyzed using the Chi-square analysis.2、Western Blot and RT-PCR were used to detect the expression of MCT4in OSCC cell lines and to detect the expression changes of MCT4after specific siRNA transfection. Medium lactate measurement, CCK8assay, transwell and wound healing assay were used to determine the effects of MCT4on cell lactate release, proliferation, migration and invasion abilities.3、Western Blot was used to detect the expression level of integrin β4, E-cadherin, N-cadhern and vimentin and to detect the phosphorylation and total levels of FAK, SRC, MEK and ERK1/2in OSCC cells with MCT4knocked down.Results1、Immunohistochemical staining results showed that MCT4was mainly expressed in cell membranes and it was strongly positive in41/99OSCC specimens, weakly positive in58/99OSCC specimens. MCT4expression was found to be positively correlated with tumor size, TNM classification, lymphatic metastasis, distant metastasis and tumor recurrence (p<0.001). MCT4was also an independent prognosis factor of OS(p=0.002) and DFS (p=0.003) in OSCC patients by multivariate survival analysis.2、Western Blot indicated MCT4was strongly expressed in HN4, HN6, and SCC9, moderately expressed in Ca127and SCC25, and exhibited low expression in HN12. The expression of MCT4in HN4and HN6was significantly inhibited after specific siRNA transfection in vitro as determined by western blot and real-time RCR. Lactate release, as well as proliferation, invasion and migration were remarlably suppressed after MCT4inhibition by siRNA in vitro.3、The expression of integrin β4, as well as the phosphorylation of FAK-Tyr397, FAK-Tyr925, SRC, MEK and ERK1/2were suppressed with MCT4knocked down. E-cadherin was increased and N-cadherin was decreased after MCT4was silenced.Conclusions1、MCT4is highly expressed in OSCC specimens and OSCC cell lines. This over-expression of MCT4was closely associated with tumor size, TNM classification, lymphatic metastasis, distant metastasis and tumor recurrence, and also poor prognosis.2、MCT4is involved in cell proliferation, migration and invasion in OSCC cells.3、The restrained intracellular link of integrin β4to SRC-FAK and MEK-ERK induced by MCT4silencing might explain the decreased proliferation, migration, and invasion ability observed in OSCC cell lines.