Abstract B40: Up-regulation of TLR1, TLR2 and TLR4 expression in innate immune cells induced by TPA: Role in the potentiation of inflammatory and oxidative stress responses to LPS and LTA

Studies have linked persisting inflammatory profiles of cytokines and oxidative stress to carcinogenic processes associated with exposure to environmental agents. Because, lipopolysaccharide (LPS) potentiates 12-otetradecanoylphorbol 13-acetate (TPA)-induced inflammation-dependent skin carcinoma, we hypothesized that one possible mechanism of this potentiation is by the activation of the innate immune cells through specific toll-like receptor (TLR). Herein, our data show that TPA-treated human myeloid cells, ML-1 exhibit robust production of inflammatory cytokines including TNF-α and interleukins as well as an increased generation of reactive oxygen species (ROS) in response to LPS and LTA respectively ligands for TLR4 and TLR2. This increased responsiveness to LPS and LTA correlated with the up-regulation of TLR1, TLR2, TLR4 and CD14 expression at both mRNA and protein levels in ML-1 cells induced by TPA. Interestingly, TLR1, TLR2 and TLR4 protein expression on ML-1 cell surface could be blocked by pretreatment with U0126 (an inhibitor of extracellular signal-regulated kinases, ERK), suggesting the role of Erk1/2-induced differentiation signal in this process. In addition, IRAK-2, a key member of the TLR/IRAK-2/NF-κB-dependent signaling cascade was also induced to express at mRNA level in response to TPA. Furthermore, the ROS generation in response to LPS and LTA was linked to NAD(P)H-dependent enzymes, as treatment with DPI significantly inhibited ROS generation. Together, these data provide evidence that TPA induces the up-regulation of TLR1, TLR2, TLR4 and CD14 gene expression at both mRNA and protein levels in immune cells. This leads to robust inflammatory cytokines production and ROS generation by innate immune cell activation.