TMEM98 mRNA promotes proliferation and invasion of gastric cells by directly interacting with NF90 protein

Transmembrane protein 98 (TMEM98) is a recently discovered gene, the inhibition of which has preliminarily been demonstrated to inhibit progression of several solid cancers in vitro. However, its involvement in tumorigenesis of gastric cancer (GC) has not been reported. Here, we aimed to explore the expression of TMEM98 in GC tissues and cell lines and to determine the role of TMEM98 in GC cell proliferation and invasion. TMEM98 was significantly upregulated in GC tissues, which was associated with low survival rate of GC patients. Interestingly, GC cell proliferation and invasion were promoted by TMEM98 messenger RNA (mRNA) upregulation and inhibited by TMEM98 mRNA downregulation, but not affected by TMEM98 protein. Using RNA-binding protein immunoprecipitation assay and RNA pull-down assay, we demonstrated that TMEM98 mRNA could directly bind with and upregulate nuclear factor 90 (NF90). Similarly, NF90 protein could not only enhance the stability of TMEM98 mRNA but antagonize the suppressive effect of TMEM98-small interfering RNA on proliferation and invasion in MKN-45 cells. Moreover, RNA pull-down assay, with wild-type (WT) and binding-site-mutated biotinylated TMEM98 mRNA transcripts, demonstrated that WT TMEM98 mRNA bound with NF90 protein through an 8-nt motif at the last exon, but the motif mutation abolished the capacity of TMEM98 mRNA binding to NF90 protein. Furthermore, overexpression of the WT last exon of TMEM98 increased NF90 expression and cell proliferation/invasion expectedly, but overexpression of the mutated last exon had no obvious effect. In conclusion, TMEM98 mRNA enhanced the proliferation and invasion of GC cells by interacting with the NF90 protein.