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,...

SUMMARY PIK3CA and PTEN alterations are common in human cancer, but only a fraction of such tumors are dependent upon AKT signaling. AKT-independence is associated with redundant activation of cap-dependent translation mediated by convergent regulation of the translational repressor 4E-BP1 by the AKT and ERK pathways. This provides mechanistic bases for the limited activity of AKT and MEK inhibitors in tumors with co-mutation of both pathways and the profound synergy observed with combined inhibition. Whereas such tumors are sensitive to a dominant active 4E-BP1 mutant, knockdown of 4E-BP1 expression reduces their dependence on AKT/ERK signaling for translation or survival. Thus, 4E-BP1 plays a prominent role in mediating the effects of these pathways in tumors in which they are activated by mutation.

SUMMARY Non-steroidal anti-inflammatory drugs (NSAIDs) exert their anti-cancer effects through cyclooxygenase-2 (COX-2)-dependent and -independent mechanisms. Here we report that Sulindac, an NSAID, induces apoptosis by binding to retinoid X receptor-α (RXRα). We identified an N-terminally-truncated RXRα (tRXRα) in several cancer cell lines and primary tumors, which interacted with the p85α subunit of phosphatidylinositol-3-OH kinase (PI3K). Tumor necrosis factor-α (TNFα) promoted tRXRα interaction with the p85α, activating PI3K/AKT signaling. When combined with TNFα, Sulindac inhibited TNFα-induced tRXRα/p85α interaction, leading to activation of the death receptor-mediated apoptotic pathway. We designed and synthesized a Sulindac analog K-80003, which has increased affinity to RXRα but lacks COX inhibitory activity. K-80003 displayed enhanced efficacy in inhibiting tRXRα-dependent AKT activation and tRXRα tumor growth in animals.

Metabolic reprogramming has been widely recognized as a hallmark of malignancy. The uptake and metabolism of amino acids are aberrantly upregulated in many cancers that display addiction to particular amino acids. Amino acids facilitate the survival and proliferation of cancer cells under genotoxic, oxidative, and nutritional stress. Thus, targeting amino acid metabolism is becoming a potential therapeutic strategy for cancer patients. In this review, we will systematically summarize the recent progress of amino acid metabolism in malignancy and discuss their interconnection with mammalian target of rapamycin complex 1 (mTORC1) signaling, epigenetic modification, tumor growth and immunity, and ferroptosis. Finally, we will highlight the potential therapeutic applications.

Genistein, a flavonoid in legumes and some herbal medicines, has various biological actions. However, studies on whether genistein has an effect on pancreatic beta-cell function are very limited. In the present study, we investigated the effect of genistein on beta-cell proliferation and cellular signaling related to this effect and further determined its antidiabetic potential in insulin-deficient diabetic mice. Genistein induced both INS1 and human islet beta-cell proliferation after 24 h of incubation, with 5 mum genistein inducing a maximal 27% increase. The effect of genistein on beta-cell proliferation was neither dependent on estrogen receptors nor shared by 17beta-estradiol or a host of structurally related flavonoid compounds. Pharmacological or molecular intervention of protein kinase A (PKA) or ERK1/2 completely abolished genistein-stimulated beta-cell proliferation, suggesting that both molecules are essential for genistein action. Consistent with its effect on cell proliferation, genistein induced cAMP/PKA signaling and subsequent phosphorylation of ERK1/2 in both INS1 cells and human islets. Furthermore, genistein induced protein expression of cyclin D1, a major cell-cycle regulator essential for beta-cell growth. Dietary intake of genistein significantly improved hyperglycemia, glucose tolerance, and blood insulin levels in streptozotocin-induced diabetic mice, concomitant with improved islet beta-cell proliferation, survival, and mass. These results demonstrate that genistein may be a natural antidiabetic agent by directly modulating pancreatic beta-cell function via activation of the cAMP/PKA-dependent ERK1/2 signaling pathway.