TRB3 overexpression due to endoplasmic reticulum stress inhibits AKT kinase activation of tongue squamous cell carcinoma

Our investigation aims to evaluate the significance of TRB3, an endoplasmic reticulum stress (ERS)-inducible gene, and explore its relationship with AKT in oral tongue squamous cell carcinoma (OTSCC). Expression of TRB3 and phosphorylated AKT (p-AKT) in OTSCC tissues and adjacent normal tissues were assessed by RT-PCR, Western blot and immunohistochemistry assay. Correlation of TRB3 and AKT was validated by TRB3 adenovirus plasmid (Ad-TRB3) transfection and short hairpin RNA (shRNA) inhibition. The mRNA expression of TRB3 was significantly higher than adjacent noncancerous tissues by RT-PCR in 15 of 18 specimens of OTSCC (83.3%, P < 0.01). Both of TRB3 and AKT were highly expressed in 13 of 18 (72.2%) specimens of OTSCC comparing with adjacent noncancerous tissues by Western blot assay (P < 0.05). TRB3 was significantly elevated in 49.2% (63/128) of pathologically confirmed specimens and 13.3% (4/30) of adjacent noncancerous specimens by immunohistochemical analysis (P < 0.01). TRB3 overexpression was closely correlated with tumor pathological T stage, lymph node metastasis and tumor recurrence. In addition, both mRNA and protein expression of TRB3 was increased under thapsigargin (TG) or tunicmycin (TU)-induced ERS in Tca8113 and CAL-27 cells. Moreover, expression of p-AKT protein decreased when Ad-TRB3 was transected with OTSCC Tca8113 cells. However, expression of p-AKT protein increased when TRB3 was inhibited by TRB3 shRNA inhibition. TRB3 expression was closely correlated with OTSCC prognosis. Under ERS, TRB3 was up-regulated, resulting in inhibiting the activation of AKT in OTSCC. (C) 2011 Elsevier Ltd. All rights reserved.