Stress-activated kinase pathway alteration is a frequent event in bladder cancer

Abstract

ObjectivesThe stress-activated MAP kinases (SAPK) signaling pathways play a critical role in the cellular response to toxins and physical stress, mediate inflammation, and modulate carcinogenesis and tumor metastasis. The stress-activated MAP kinases (MAPK) c-Jun N-terminal kinase (JNK) and p38 are activated upon phosphorylation by a widely expressed and conserved family of upstream MAP kinase kinases (MAP2K). Signaling mediated by p38 and JNK has well-established importance in cancer, yet the contribution of this pathway in urothelial bladder cancer is not understood. This study evaluated stress-activated MAP kinase pathway expression in cell lines derived from human urothelial carcinomas. Materials and methodsTotal protein lysates from a panel of human urothelial bladder cancer cell lines (RT4, T24, UMUC-3, J82, 5637, 253J, and 253J-BV) were analyzed by immunoblotting for the JNK and p38 MAPKs, as well as MKK3, MKK4, MKK6, and MKK7. Quantitative real time PCR was utilized to determine mRNA expression levels of the MAP2Ks. Stress stimuli (sorbitol, hydrogen peroxide, and UV irradiation) were used to active p38, which was measured by phospho-antibody. ResultsAlthough protein levels were variable, all cell lines expressed p38 and JNK. On the other hand, with the exception of the well-differentiated cell line RT4, each cell line had a reduction or absence of expression of one or more MAP2K. 253J and 253J-BV exhibited no expression of MKK6, even when an excess of protein was queried. mRNA levels indicated that both transcriptional and post-transcriptional mechanisms are involved in the regulation of MAP2Ks. Decreased MAP2K expression correlated with decreased ability to activate p38 in response to stress stimuli. ConclusionsAberrant MAP2K protein expression indicates that altered cellular signal transduction mediated via JNK and p38 may be common in bladder cancer. Down-regulation of MAP2Ks likely occurs at both the transcriptional and post-transcriptional levels. Consistent with the known function of p38 and JNK in apoptosis, defects in normal pathway function caused by decreased expression of upstream MAP2Ks may provide a survival advantage to bladder cancer cells. Further investigations should focus on identifying a functional role for these pathways in bladder cancer development.