FIGURE 4: Model of p38 and mTORC1-mediated regulation of PDCD4. LPS activates Toll-like receptor 4 (TLR4) signaling. Subse-quent signal transmission via phosphoinositide 3-kinase (PI3K) and mitogen-activated kinase p38 leads to inhibition of the sup-pressor protein tuberous sclerosis complex 2 (TSC2), followed by activation of mammalian target of rapamycin complex 1 (mTORC1). mTORC1 phosphorylates ribosomal protein S6 kinase beta-1 (S6K1), which in turn phosphorylates programmed cell death protein 4 (PDCD4). PDCD4 is ubiquitinated and degraded by the proteasome.