Upregulation of nuclear factor-κB expression by SLURP-1 is mediated by α7-nicotinic acetylcholine receptor and involves both ionic events and activation of protein kinases

Chernyavsky AI, Arredondo J, Galitovskiy V, Qian J, Grando SA. Upregulation of nuclear factor-kappa B expression by SLURP-1 is mediated by alpha(7)-nicotinic acetylcholine receptor and involves both ionic events and activation of protein kinases. Am J Physiol Cell Physiol 299: C903-C911, 2010. First published July 21, 2010; doi: 10.1152/ajpcell.00216.2010.-SLURP-1 (secreted mammalian Ly-6/urokinase plasminogen activator receptor-related protein-1) is a novel auto/paracrine cholinergic peptide that can bind to alpha(7)-nicotinic acetylcholine receptor (nAChR), a high Ca2+-permeable ion channel coupled to regulation of nuclear factor-kappa B (NF-kappa B) expression. Elucidation of intracellular signaling events elicited by SLURP-1 is crucial for understanding the molecular mechanism of functioning of this novel hormone-like peptide that alters vital cell functions and can protect from tumorigenic transformation. In this study, we sought to dissect out the role of alpha(7)-nAChR in mediating the biologic effects of recombinant SLURP-1 on the immortalized line of human oral keratinocytes Het-1A. A multifold upregulation of the NF-kappa B expression at the mRNA and protein levels by SLURP-1 was only slightly diminished due to elimination of Na+, whereas in Ca2+-free medium the effect of SLURP-1 was inhibited by >50%. Both in the absence of extracellular Ca2+ and in the presence of Cd2+ or Zn2+, the SLURP-1-dependent elevation of NF-kappa B was almost completely blocked by inhibiting MEK1 activity. Downstream of alpha(7)-nAChR, the SLURP-1 signaling coupled to upregulation of NF-kappa B also involved Jak2 as well as Ca2+/calmodulin-dependent kinase II (CaMKII) and protein kinase C (PKC), whose inhibition significantly (P < 0.05) reduced the SLURP-1-induced upregulation of NF-kappa B. The obtained results indicated that activation of alpha(7)-nAChR by SLURP-1 leads to upregulation of the NF-kappa B gene expression due to activation of the Raf-1/MEK1/ERK1/2 cascade that proceeds via two complementary signaling pathways. One is mediated by the Ca2+-entry dependent CaMKII/PKC activation and another one by Ca2+-independent involvement of Jak2. Thus, there exists a previously not appreciated network of noncanonical auto/paracrine ligands of nAChR of the Ly-6 protein family, which merits further investigations.