Temozolomide-modulated glioma proteome: Role of interleukin-1 receptor-associated kinase-4 (IRAK4) in chemosensitivity

The current treatment for glioblastoma includes temozolomide (TMZ) chemotherapy, yet the mechanism of action of TMZ is not thoroughly understood. Here, we investigated the TMZ-induced changes in the proteome of the glioma-derived cell line (U251) by 2D DIGE. We found 95 protein spots to be significantly altered in their expression after TMZ treatment. MS identified four upregulated spots: aspartyl tRNA synthetase glutathione synthetase, interleukin-1 receptor-associated kinase-4 (IRAK4), and breast carcinoma amplified sequence-1 and one downregulated spot: optineurin. TMZ-induced regulation of these five genes was validated by RT-qPCR and Western blot analysis. RNAi-mediated knockdown of IRAK4, an important mediator of Toll-like receptors signaling and chemoresistance, rendered the glioma cells resistant to TMZ. High levels of IRAK4 induced upon TMZ treatment resulted in IRAK1 downregulation and inhibition of NFkB pathway. Endogenous IRAK4 protein, but not transcript levels in glioma cell lines, correlated with TMZ sensitivity. Thus, we have identified several TMZ-modulated proteins and discovered an important novel role for IRAK4 in determining TMZ sensitivity of glioma cells through its ability to inhibit Toll-like receptor signaling and NFkB pathway.