Role of folliculin in interferon-γ-mediated apoptosis of and chemokine secretion by melanocytes / 中华皮肤科杂志

ABSTRACT

Objective:To investigate the role of folliculin in apoptosis of and chemokine secretion by melanocytes mediated by interferon-γ (IFN-γ) .Methods:Normal primary melanocytes were isolated from circumcised foreskin tissues from a healthy male child, and primary vitiliginous melanocytes were isolated from normally pigmented suction-blistered epidermis from patients with vitiligo after suction blister epidermal grafting. Western blot analysis was performed to determine the folliculin protein expression in normal primary melanocytes, primary vitiliginous melanocytes and a human primary melanocyte line PIG1. PIG1 cells stimulated with 10 ng/ml IFN-γ for 48 hours served as induction group, and untreated PIG1 cells served as control group. Real-time quantitative RCR (qRT-PCR) was performed to determine the mRNA expression of folliculin, autophagy-related microtubule-associated protein 1 light chain 3 (LC3) -Ⅱ and Beclin genes, and Western blot analysis to determine the protein expression of folliculin, Beclin1 and LC3Ⅱ/Ⅰ, as well as phosphorylation levels of adenosine monophosphate-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) in the above cells. Furthermore, the melanocytes stimulated with 10 ng/ml IFN-γ for 48 hours were divided into several groups negative control group infected with an empty lentiviral vector, folliculin inhibition group infected with a folliculin-inhibiting lentivirus, autophagy enhancement group infected with a folliculin-inhibiting lentivirus followed by 2-hour treatment with a mTOR inhibitor, autophagy inhibition group infected with a folliculin-inhibiting lentivirus followed by 2-hour treatment with an AMPK inhibitor. Then, flow cytometry was conducted to detect apoptosis of PIG1 cells, and enzyme-linked immunosorbent assay to measure the concentration of chemokines CXCL10 and CCL20 in the culture supernatant of PIG1 cells in the above groups. Measurement data were compared among multiple groups by using one-way analysis of variance, and multiple comparisons were carried out by using least significant difference- t test. Results:The relative protein expression level of folliculin significantly differed among the normal primary melanocytes (0.850 ± 0.120) , primary vitiliginous melanocytes (1.507 ± 0.170) and PIG1 cells (0.697 ± 0.130; F = 50.09, P < 0.001) , and was significantly higher in the primary vitiliginous melanocytes than in the normal primary melanocytes and PIG1 cells ( t = 4.06, 5.89, respectively, both P < 0.01) . Compared with the control group, the induction group showed significantly increased relative mRNA and protein expression levels of folliculin (both P < 0.01) , but significantly decreased relative mRNA and protein expression levels of LC3Ⅱ and Beclin (all P < 0.01) ; moreover, the induction group showed significantly decreased LC3Ⅱ/Ⅰ levels (0.72 ± 0.02) and AMPK phosphorylation levels (0.714 ± 0.023) in the PIG1 cells compared with the control group (1.13 ± 0.02, 1.176 ± 0.002, t = 7.34, 6.67, respectively, both P < 0.01) , but significantly increased mTOR phosphorylation levels (1.051 ± 0.023) compared with the control Group (0.451 ± 0.016, t = 3.81, P = 0.009) . There were significant differences in the PIG1 cell apoptosis rate and concentrations of CXCL10 and CCL20 among the control group, induction group and other treatment groups (all P < 0.001) ; specifically, the PIG1 cell apoptosis rate and concentrations of CXCL10 and CCL20 were significantly higher in the induction group than in the control group, lower in the folliculin inhibition group than in the negative control group, lower in the autophagy enhancement group than in the folliculin inhibition group, and higher in the autophagy inhibition group than in the folliculin inhibition group (all P < 0.05) . Conclusions:Folliculin is highly expressed in vitiliginous melanocytes. Folliculin expression and downstream signaling pathways are regulated by IFN-γ, and folliculin may participate in IFN-γ-mediated melanocyte apoptosis and chemokine secretion via regulating autophagy.