A Preliminary Study On The Clinical Significance And Mechanism Of PD-L1 In Medullary Thyroid Carcinoma

Objective: To explore the clinical significance of programmed cell death-ligand 1(PD-L1)in medullary thyroid carcinoma(MTC)and its abnormal express influence on migration,invasiveity and proliferation of medullary thyroid carcinoma TT cells.And explore the relationship between PD-L1 and signal transducer and activator of transcription 3(STAT3)to understand its mechanism of invasion and metastasis in medullary thyroid carcinoma TT cells preliminarily.Methods:1.36 MTC cases were collected from June 2016 to June 2019 in the Department of Thyroid Surgery,the fourth clinical Medical College of Qingdao University(Yantai Yuhuangding Hospital).All patients were as follows: detailed clinical diagnosis and treatment data,complete postoperative specimens,no distant metastasis,and paraffin pathological confirmed the lesion was MTC.A total of 36 cases were eligible.Immunohistochemistry(IHC)was detected the expression of PD-L1 protein in 36 MTC tissues and their normal thyroid tissues that adjacent to cancer(CNT),and analyzing the relationship between PD-L1 and clinicopathological characteristics in MTC patients.2.TT cells were transfected with plasmid and divided into blank control groups(BCG),NC empty vector group(NEVG),NC si RNA group(NSG),PD-L1 overexpression group(POG)and PD-L1 low expression group(PLG).The relative expression of PD-L1 protein before and after transfected TT cells was detected by Western Blot(WB).Quantitative real-time PCR(q RT-PCR)was used to detect the expression of PD-L1 m RNA in each group of TT cells after transfection.The purpose of WB and q RT-PCR were to detect transfection efficiency.Scratch test,Transwell technique and CCK-8 method were used to detect the effects of PD-L1 on the functions of TT cells in different groups.3.The expression of phospho-STAT3(P-STAT3)and STAT3 protein in different groups of TT cells were determined by WB to explore the mechanism of PD-L1 and STAT3 in TT cells preliminarily.Results:1.The expression rate of PD-L1 in the 36 MTC tissues was 61.11%(22/36),while it was only 16.67%(6/36)in CNT tissues,the difference was statistically significant(P<0.001). Statistics showed that the positive expression of PD-L1 protein in 36 patients was related to thyroid capsule invasion and cervical lymph node metastasis in clinicopathological characteristics(P<0.05);but not with the age,gender,tumor size,and TNM stage of MTC patients(P>0.05).2.The Scratch test,Transwell technique and CCK-8 method showed that: PD-L1 can promote the migration,invasion and proliferation of TT cells.3.WB analysis showed that the expression of P-STAT3 protein in POG was significantly higher than that of NEVG and PLG(P<0.05),while the total expression of STAT3 protein was not significantly different in transfected TT cells(P>0.05).Conclusions:1.The positive expression rate of PD-L1 protein in MTC tissue is significantly higher than that in CNT tissue.The positive expression of PD-L1 protein is related to thyroid capsule invasion and neck lymph node metastasis in MTC patients.2.PD-L1 overxpression promotes the phosphorylation of STAT3 protein in TT cells,and it also enhances the migration,invasion and proliferation of TT cells.The mechanism of invasion and metastasis in TT cells may be related to the activation of STAT3 pathway.