Birt-Hogg-Dubé syndrome, a hamartoma disorder characterized by benign tumors of the hair follicle, lung cysts, and renal neoplasia, is caused by germ-line mutations in the BHD(FLCN) gene, which encodes a tumor-suppressor protein, folliculin (FLCN), with unknown function. The tumor-suppressor proteins encoded by genes responsible for several other hamartoma syndromes, LKB1, TSC1͞2, and PTEN, have been shown to be involved in the mammalian target of rapamycin (mTOR) signaling pathway. Here, we report the identification of the FLCN-interacting protein, FNIP1, and demonstrate its interaction with 5 AMP-activated protein kinase (AMPK), a key molecule for energy sensing that negatively regulates mTOR activity. FNIP1 was phosphorylated by AMPK, and its phosphorylation was reduced by AMPK inhibitors, which resulted in reduced FNIP1 expression. AMPK inhibitors also reduced FLCN phosphorylation. Moreover, FLCN phosphorylation was diminished by rapamycin and amino acid starvation and facilitated by FNIP1 overexpression, suggesting that FLCN may be regulated by mTOR and AMPK signaling. Our data suggest that FLCN, mutated in Birt-Hogg-Dubé syndrome, and its interacting partner FNIP1 may be involved in energy and͞or nutrient sensing through the AMPK and mTOR signaling pathways.hamartoma syndrome ͉ renal cancer ͉ Birt-Hogg-Dubé ͉ tumor suppressor B irt-Hogg-Dubé (BHD) syndrome predisposes patients to develop hair follicle hamartomas, lung cysts, and an increased risk for renal neoplasia (1-3). BHD patients develop bilateral, multifocal renal tumors with a variety of histologies (4). We mapped the BHD locus to chromosome 17p11.2 by linkage analysis in BHD kindreds (5, 6) and identified germ-line mutations in a gene with unknown function that is highly conserved (7,8). Twenty-two unique mutations predicted to truncate the BHD protein folliculin (FLCN), including a ''hot spot'' insertion͞deletion in a C 8 tract, were identified in 84% of BHD kindreds (9). Somatic ''second-hit'' mutations identified in BHD-associated renal tumors suggest a tumor-suppressor function for FLCN (10), underscored by loss of BHD mRNA expression in renal tumors from BHD patients (11).Recent studies suggest that several hamartoma syndromes may be linked through the convergent energy͞nutrient-sensing pathways involved in mammalian target of rapamycin (mTOR) regulation (12-15). These inherited syndromes are characterized by multiple hamartomas and an increased risk of cancer. Germ-line mutations have been identified in four causative genes: LKB1, responsible for Peutz-Jeghers syndrome (16-18), TSC1 and TSC2, responsible for tuberous sclerosis complex (TSC) (19), and PTEN, responsible for Cowden syndrome (20). Loss of gene function leads to dysregulation of mTOR, which regulates cell growth and size through stimulation of protein synthesis (15, 21, 22).BHD syndrome, also a hamartoma disorder, displays phenotypic similarities to TSC that have led to speculation that BHD may function in the pathway(s) signaling through mTOR (12,23). To ascertain FLCN function,...

Objective. Stromal cell-derived factor 1 (SDF-1; CXCL12/pre-B cell growth-stimulating factor) is a dominant chemokine in bone marrow and is known to be involved in inflammatory diseases, including rheumatoid arthritis. However, its role in bone repair remains unknown. The purpose of this study was to investigate the role of SDF-1 and its receptor, CXCR4, in bone healing.Methods. The expression of SDF-1 during the repair of a murine structural femoral bone graft was examined by real-time polymerase chain reaction and immunohistochemical analysis. The bone graft model was treated with anti-SDF-1 neutralizing antibody or TF14016, an antagonist for CXCR4, and evaluated by histomorphometry. The functional effect of SDF-1 on primary mesenchymal stem cells was determined by in vitro and in vivo migration assays. New bone formation in an exchanging-graft model was compared with that in the autograft models, using mice partially lacking SDF-1 (SDF-1 ؉/؊ ) or CXCR4 (CXCR4 ؉/؊ ).Results. The expression of SDF1 messenger RNA was increased during the healing of live bone grafts but was not increased in dead grafts. High expression of SDF-1 protein was observed in the periosteum of the live graft. New bone formation was inhibited by the administration of anti-SDF-1 antibody or TF14016. SDF-1 increased mesenchymal stem cell chemotaxis in vitro in a dose-dependent manner. The in vivo migration study demonstrated that mesenchymal stem cells recruited by SDF-1 participate in endochondral bone repair. Bone formation was decreased in SDF-1 ؉/؊ and CXCR4 ؉/؊ mice and was restored by the graft bones from CXCR4 ؉/؊ mice transplanted into the SDF-1 ؉/؊ femur, but not vice versa.Conclusion. SDF-1 is induced in the periosteum of injured bone and promotes endochondral bone repair by recruiting mesenchymal stem cells to the site of injury.

Steady-state egress of hematopoietic progenitor cells can be rapidly amplified by mobilizing agents such as AMD3100, the mechanism, however, is poorly understood. We report that AMD3100 increased the homeostatic release of the chemokine SDF-1 to the circulation in mice and non-human primates. Neutralizing antibodies against CXCR4 or SDF-1 inhibited both steady-state and AMD3100-induced SDF-1 release and reduced egress of murine progenitor cells over mature leukocytes. Intra-bone injection of biotinylated SDF-1 also enhanced release of this chemokine and murine progenitor cell mobilization. AMD3100 directly induced SDF-1 release from CXCR4+ human bone marrow osteoblasts and endothelial cells and activated uPA in a CXCR4/JNK-dependent manner. Additionally, ROS inhibition reduced AMD3100-induced SDF-1 release, activation of circulating uPA and mobilization of progenitor cells. Norepinephrine treatment, mimicking acute stress, rapidly increased SDF-1 release and progenitor cell mobilization, while β2-adrenergic antagonist inhibited both steady-state and AMD3100-induced SDF-1 release and progenitor cell mobilization in mice. In conclusion, this study reveals that SDF-1 release from bone marrow stromal cells to the circulation emerges as a pivotal mechanism essential for steady state egress and rapid mobilization of hematopoietic progenitor cells, but not mature leukocytes.