Folliculin (FLCN) is the tumor suppressor associated withBirt-Hogg-Dubé (BHD) syndrome that predisposes patients to incident of hamartomas and cysts in multiple organs. Its inactivation causes deregulation in the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. However, the underlying mechanism is poorly defined. In this study, we show that FLCN is a ciliary protein that functions through primary cilia to regulate mTORC1. In response to flow stress, FLCN associates with LKB1 and recruits the kinase to primary cilia for activation of AMPK resided at basal bodies, which causes mTORC1 down-regulation. In cells depleted of FLCN, LKB1 fails to accumulate in primary cilia and AMPK at the basal bodies remains inactive, thus nullifying the inhibitory effect of flow stress on mTORC1 activity. Our results demonstrate that FLCN is part of a flow sensory mechanism that regulates mTORC1 through primary cilia. Birt-Hogg-Dubé (BHD)4 syndrome is a rare autosomal dominant genetic disorder characterized by development of hamartomas and cysts in multiple organs, including skin, lung, colon, and kidney (1, 2). The syndrome is caused by germ-line mutations in the BHD gene, which encodes the folliculin protein (FLCN), a 64-kDa polypeptide that shares little sequence similarity with any other known proteins (3). FLCN is found to complex with AMPK and FNIP1, although the significance of the complex for FLCN function remains unclear (4). In mouse models FLCN deficiency leads to development of polycystic kidneys and renal cell carcinoma that are characteristically similar to those found in BHD patients (5, 6). Inactivation of FNIP1, together with its homolog FNIP2, in mice also produces similar phenotypes as does by FLCN deficiency (7), suggesting that FNIP1 may be required for FLCN function. Analyses of tumors derived from BHD patients and FLCN deficient animals have revealed deregulation in mammalian target of rapamycin complex 1 (mTORC1) signaling, a key event in tumorigenesis (5, 8 -12). This abnormality in mTORC1 signaling is believed to be a major contributor to the pathological conditions in BHD, as inhibition of mTORC1 with rapamycin has been found to reduce the BHD tumor growth in animal models (5, 6). However, the mechanism by which FLCN regulates mTORC1 remains poorly understood.At non-cycling resting state, most eukaryotic cells possess a microtubule-based membranous protrusion from cell surface termed as primary cilium (13). This unique structure plays a critical role in maintaining tissue homeostasis by functioning as a sensor for extracellular fluidic shear stress and chemicals (14, 15). Many signaling pathways involved in cell growth and proliferation are regulated by this environmental sensor, among which is the mTORC1 pathway (16 -18). Several upstream regulators of mTORC1 have been found to localize to primary cilia, including the tuberous sclerosis complex proteins, LKB1 and AMPK (19 -21). A recent study has shown that primary cilia are able to act through a LKB1-and AMPK-dependent mechanism to dow...

Accumulating evidence shows that RAGE has an important function in the pathogenesis of sepsis. However, the mechanisms by which RAGE transduces signals to downstream kinase cascades during septic shock are not clear. Here, we identify SLP76 as a binding partner for the cytosolic tail of RAGE both in vitro and in vivo and demonstrate that SLP76 binds RAGE through its sterile α motif (SAM) to mediate downstream signaling. Genetic deficiency of RAGE or SLP76 reduces AGE-induced phosphorylation of p38 MAPK, ERK1/2 and IKKα/β, as well as cytokine release. Delivery of the SAM domain into macrophages via the TAT cell-penetrating peptide blocks proinflammatory cytokine production. Furthermore, administration of TAT-SAM attenuates inflammatory cytokine release and tissue damage in mice subjected to cecal ligation and puncture (CLP) and protects these mice from the lethality of sepsis. These findings reveal an important function for SLP76 in RAGE-mediated pro-inflammatory signaling and shed light on the development of SLP76-targeted therapeutics for sepsis.

Angiotensin II has progressively been considered to play an important role in the development of liver fibrosis, although the mechanism isn't fully understood. The aim of this study was to investigate a possible pro-fibrotic mechanism, by which angiotensin II would enhance the pro-fibrotic effect of transforming growth factor beta 1 (TGF-β1) through up-regulation of toll-like receptor 4 (TLR4) and enhancing down-regulation of TGF-β1 inhibitory pseudo-receptor—BAMBI caused by LPS in hepatic stellate cells (HSCs). Firstly, the synergistic effects of angiotensin II, TGF-β1 and LPS on collagen 1α production were confirmed in vitro by ELISA, in which angiotensin II, LPS and TGF-β1 were treated sequentially, and in vivo by immunofluorescence, in the experiments single or multiple intra-peritoneally implanted osmotic mini-pumps administrating angiotensin II or LPS combined with intra-peritoneal injections of TGF-β1 were used. We also found that only LPS and TGF-β1 weren't enough to induce obvious fibrogenesis without angiotensin II. Secondly, to identify the reason of why angiotensin II is so important, the minute level of TLR4 in activated HSCs - T6 and primary quiescent HSCs of rat, up-regulation of TLR4 by angiotensin II and blockage by different angiotensin II receptor type 1 (AT1) blockers in HSCs were assayed by western blotting in vitro and immunofluorescence in vivo. Finally, BAMBI expression level, which is regulated by LPS-TLR4 pathway, was detected by qRT-PCR and results showed angiotensin II enhanced the down-regulation of BAMBI mRNA caused by LPS in vitro and in vivo, and TLR4 neutralization antibody blocked this interactive effect. These data demonstrated that angiotensin II enhances LPS-TLR4 pathway signaling and further down-regulates expression of BAMBI through up-regulation of TLR4, which results in facilitation of pro-fibrotic activity of TGF-β1. Angiotensin II, LPS and TGF-β1 act synergistically during hepatic fibrogenesis, showing crosstalks between angiotensin II-AT1, LPS-TLR4 and TGF-β1-BAMBI signal pathways in rat HSCs.