Analysis of regulatory mechanisms of expression of apoptosis inducing factor GRIM-19

GRIM-19（与类维生素A-IFN-诱导的死亡相关的基因19）编码16 kDa蛋白，其最初作为干扰素-β（IFN-β）-和视黄酸（RA）-诱导的细胞死亡途径中的生长抑制基因产物分离。GRIM-19已显示通过与致癌转录因子STAT 3相互作用并由此抑制STAT 3调节的基因表达来抑制肿瘤细胞生长并诱导细胞凋亡。本研究旨在探讨GRIM-19在口腔鳞状细胞癌（OSCC）细胞中的表达及其功能。结果表明：1）Western blotting检测GRIM-19在OSCC细胞系中的表达，IFN-β和RA共刺激可诱导Ca 9 -22细胞中GRIM-19蛋白的显著表达。然而，在来自用IFN-β和RA 2刺激的HSC-2细胞的细胞裂解物中观察到GRIM-19的仅边缘表达。尽管在HSC-2和Ca 9 -22细胞中均检测到组成型GRIM-19 mRNA表达，但IFN-β和RA对两种细胞中GRIM-19 mRNA的表达均无诱导作用。IFN-β诱导两种细胞中CXCL 11和TRAIL mRNA的表达，表明IFN-β信号传导途径在这些细胞中是完整的。这些结果表明GRIM-19在口腔鳞癌细胞中的表达在翻译或翻译后水平受到调控，而不是在转录水平。

GRIM-19 (gene associated with retinoid-IFN-induced mortality 19) codes for a 16 kDa protein which was originally isolated as a growth suppressive gene product in the interferon-beta (IFN-ss)- and retinoic acid (RA)-induced cell death pathway. GRIM-19 has been shown to suppress tumor cell growth and induce apoptosis by interacting with an oncogenic transcription factor STAT3 and thereby inhibiting the STAT3-regulated gene expression. The present study was undertaken to clarify the expression and functional role of GRIM-19 in oral squamous cell carcinoma (OSCC) cells and the following results were obtained.1) When expression of GRIM-19 was assessed in OSCC cell lines by Western blotting, co-stimulation with IFN-ss and RA induced a prominent GRIM-19 protein expression in Ca9-22 cells. However, an only marginal expression of GRIM-19 was observed in cell lysate from HSC-2 cells stimulated with IFN-ss and RA2). Although a constitutive GRIM-19 mRNA expression was detected in both HSC-2 and Ca9-22 cells, IFN-ss and RA had no inductive effect on the GRIM-19 mRNA expression in both cells.3). IFN-ss induced expression of CXCL11 and TRAIL mRNAs in both cells, suggesting that IFN-ss signaling pathway are intact in these cells. Taken together these results suggested that the expression of GRIM-19 in OSCC cells is regulated at translational or post-translational level but not transcriptional level.