<P> When activated, toll - like receptors (TLRs) take adapter molecules within the cytoplasm of cells in order to propagate a signal . Four adaptor molecules are known to be involved in signaling, which are Myd88, TIRAP, TRIF, and TRAM . These adapters activate other intracellular molecules such as IRAK1, IRAK4, TBK1, and IKKi that amplify the signal, eventually leading to the induction or suppression of genes that cause certain responses . Thousands of genes are activated by TLR signaling, implying that this method constitutes an important gateway for gene modulation . </P> <P> A ligand - gated ion channel, upon binding with a ligand, changes conformation to open a channel in the cell membrane through which ions relaying signals can pass . An example of this mechanism is found in the receiving cell of a neural synapse . The influx of ions that occurs in response to the opening of these channels induces action potentials, such as those that travel along nerves, by depolarizing the membrane of post-synaptic cells, resulting in the opening of voltage - gated ion channels . </P> <P> An example of an ion allowed into the cell during a ligand - gated ion channel opening is Ca; it acts as a second messenger initiating signal transduction cascades and altering the physiology of the responding cell . This results in amplification of the synapse response between synaptic cells by remodelling the dendritic spines involved in the synapse . </P> <P> Intracellular receptors, such as nuclear receptors and cytoplasmic receptors, are soluble proteins localized within their respective areas . The typical ligands for nuclear receptors are non-polar hormones like the steroid hormones testosterone and progesterone and derivatives of vitamins A and D. To initiate signal transduction, the ligand must pass through the plasma membrane by passive diffusion . On binding with the receptor, the ligands pass through the nuclear membrane into the nucleus, altering gene expression . </P>

Signal transduction pathway mechanism that affects protein expression