Decreased RNA-binding motif 5 expression is associated with tumor progression in gastric cancer

RNA-binding motif 5 is a putative tumor suppressor gene that modulates cell cycle arrest and apoptosis. We recently demonstrated that RNA-binding motif 5 inhibits cell growth through the p53 pathway. This study evaluated the clinical significance of RNA-binding motif 5 expression in gastric cancer and the effects of altered RNA-binding motif 5 expression on cancer biology in gastric cancer cells. RNA-binding motif 5 protein expression was evaluated by immunohistochemistry using the surgical specimens of 106 patients with gastric cancer. We analyzed the relationships of RNA-binding motif 5 expression with clinicopathological parameters and patient prognosis. We further explored the effects of RNA-binding motif 5 downregulation with short hairpin RNA on cell growth and p53 signaling in MKN45 gastric cancer cells. Immunohistochemistry revealed that RNA-binding motif 5 expression was decreased in 29 of 106 (27.4%) gastric cancer specimens. Decreased RNA-binding motif 5 expression was correlated with histological differentiation, depth of tumor infiltration, nodal metastasis, tumor–node–metastasis stage, and prognosis. RNA-binding motif 5 silencing enhanced gastric cancer cell proliferation and decreased p53 transcriptional activity in reporter gene assays. Conversely, restoration of RNA-binding motif 5 expression suppressed cell growth and recovered p53 transactivation in RNA-binding motif 5–silenced cells. Furthermore, RNA-binding motif 5 silencing reduced the messenger RNA and protein expression of the p53 target gene p21. Our results suggest that RNA-binding motif 5 downregulation is involved in gastric cancer progression and that RNA-binding motif 5 behaves as a tumor suppressor gene in gastric cancer.

The Nuclear Splicing Factor RNA Binding Motif 5 Promotes Caspase Activation in Human Neuronal Cells, and Increases after Traumatic Brain Injury in Mice

Splicing factors (SFs) coordinate nuclear intron/exon splicing of RNA. Splicing factor disturbances can cause cell death. RNA binding motif 5 (RBM5) and 10 (RBM10) promote apoptosis in cancer cells by activating detrimental alternative splicing of key death/survival genes. The role(s) of RBM5/10 in neurons has not been established. Here, we report that RBM5 knockdown in human neuronal cells decreases caspase activation by staurosporine. In contrast, RBM10 knockdown augments caspase activation. To determine whether brain injury alters RBM signaling, we measured RBM5/10 protein in mouse cortical/hippocampus homogenates after controlled cortical impact (CCI) traumatic brain injury (TBI) plus hemorrhagic shock (CCI+HS). The RBM5/10 staining was higher 48 to 72 hours after injury and appeared to be increased in neuronal nuclei of the hippocampus. We also measured levels of other nuclear SFs known to be essential for cellular viability and report that splicing factor 1 (SF1) but not splicing factor 3A (SF3A) decreased 4 to 72 hours after injury. Finally, we confirm that RBM5/10 regulate protein expression of several target genes including caspase-2, cellular FLICE-like inhibitory protein (c-FLIP), LETM1 Domain-Containing Protein 1 (LETMD1), and amyloid precursor-like protein 2 (APLP2) in neuronal cells. Knockdown of RBM5 appeared to increase expression of c-FLIP(s), LETMD1, and APLP2 but decrease caspase-2.