Enhanced effects of guggulsterone plus 1,25(OH)2D3 on 3T3-L1 adipocytes

Guggulsterone (GS) and 1,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] have been shown to influence adipogenesis in 3T3-L1 cells. We investigated the ability of GS and 1,25(OH)₂D₃, alone and in combination to inhibit adipogenesis and induce apoptosis in 3T3-L1 adipocytes. Maturing preadipocytes were treated with 1,25(OH)₂D₃ in combination with GS for 6 days during differentiation. GS and 1,25(OH)₂D₃ each inhibited lipid accumulation, but the combination potentiated the inhibition of lipid accumulation. Apoptosis was increased by 1,25(OH)₂D₃ while GS had no effect, but GS + 1,25(OH)₂D₃ increased apoptosis more than either compound alone. Furthermore, GS + 1,25(OH)₂D₃ caused a potentiated decrease in the expression of aP2 and farnesoid X receptor expression more than either compound alone. In addition, 1,25(OH)₂D₃ increased vitamin D receptor expression after 6 days, while GS had no effect. GS + 1,25(OH)₂D₃, however, caused a potentiated increase in the expression of VDR. These findings show that GS potentiates 1,25(OH)₂D₃’s anti-adipogenic and pro-apoptotic effects in maturing 3T3-L1 preadipocytes.     

MiR-27a Functions as a Tumor Suppressor in Acute Leukemia by Regulating 14-3-3θ

MicroRNAs (miRs) play major roles in normal hematopoietic differentiation and hematopoietic malignancies. In this work, we report that miR-27a, and its coordinately expressed cluster (miR-23a∼miR-27a∼miR-24-2), was down-regulated in acute leukemia cell lines and primary samples compared to hematopoietic stem-progenitor cells (HSPCs). Decreased miR-23a cluster expression in some acute leukemia cell lines was mediated by c-MYC. Replacement of miR-27a in acute leukemia cell lines inhibited cell growth due, at least in part, to increased cellular apoptosis. We identified a member of the anti-apoptotic 14-3-3 family of proteins, which support cell survival by interacting with and negatively regulating pro-apoptotic proteins such as Bax and Bad, as a target of miR-27a. Specifically, miR-27a regulated 14-3-3θ at both the mRNA and protein levels. These data indicate that miR-27a contributes a tumor suppressor-like activity in acute leukemia cells via regulation of apoptosis, and that miR-27a and 14-3-3θ may be potential therapeutic targets.     

Large-scale movement of functional domains facilitates aminoacylation by human mitochondrial phenylalanyl-tRNA synthetase

Structural studies suggest rearrangement of the RNA-binding and catalytic domains of human mitochondrial PheRS (mtPheRS) is required for aminoacylation. Crosslinking the catalytic and RNA-binding domains resulted in a “closed” form of mtPheRS that still catalyzed ATP-dependent Phe activation, but was no longer able to transfer Phe to tRNA and complete the aminoacylation reaction. SAXS experiments indicated the presence of both the closed and open forms of mtPheRS in solution. Together, these results indicate that conformational flexibility of the two functional modules in mtPheRS is essential for its phenylalanylation activity. This is consistent with the evolution of the aminoacyl-tRNA synthetases as modular enzymes consisting of separate domains that display independent activities.     

Susceptibility Loci Associated with Specific and Shared Subtypes of Lymphoid Malignancies

The genetics of lymphoma susceptibility reflect the marked heterogeneity of diseases that comprise this broad phenotype. However, multiple subtypes of lymphoma are observed in some families, suggesting shared pathways of genetic predisposition to these pathologically distinct entities. Using a two-stage GWAS, we tested 530,583 SNPs in 944 cases of lymphoma, including 282 familial cases, and 4,044 public shared controls, followed by genotyping of 50 SNPs in 1,245 cases and 2,596 controls. A novel region on 11q12.1 showed association with combined lymphoma (LYM) subtypes. SNPs in this region included rs12289961 near LPXN, (P_LYM = 3.89×10⁻⁸, OR = 1.29) and rs948562 (P_LYM = 5.85×10⁻⁷, OR = 1.29). A SNP in a novel non-HLA region on 6p23 (rs707824, P_NHL = 5.72×10⁻⁷) was suggestive of an association conferring susceptibility to lymphoma. Four SNPs, all in a previously reported HLA region, 6p21.32, showed genome-wide significant associations with follicular lymphoma. The most significant association with follicular lymphoma was for rs4530903 (P_FL = 2.69×10⁻¹², OR = 1.93). Three novel SNPs near the HLA locus, rs9268853, rs2647046, and rs2621416, demonstrated additional variation contributing toward genetic susceptibility to FL associated with this region. Genes implicated by GWAS were also found to be cis-eQTLs in lymphoblastoid cell lines; candidate genes in these regions have been implicated in hematopoiesis and immune function. These results, showing novel susceptibility regions and allelic heterogeneity, point to the existence of pathways of susceptibility to both shared as well as specific subtypes of lymphoid malignancy.     

A putative role for apelin in the etiology of obesity

Apelin, the endogenous ligand of the G protein-coupled APJ receptor has been shown to promote tumor angiogenesis. However, the effect of apelin on inducing angiogenesis in adipose tissue has not been investigated. In this review, we propose a putative role for apelin in promoting angiogenesis in adipose tissue. We further propose that targeting adipose tissue vasculature by blocking apelin signaling with anti-apelin antibodies will lead not only to inhibition of angiogenesis in adipose tissue but also to decreased adiposity.     

Unexpected role of ceruloplasmin in intestinal iron absorption

Ferroxidases are essential for normal iron homeostasis in most organisms. The paralogous vertebrate ferroxidases ceruloplasmin (Cp) and hephaestin (Heph) are considered to have nonidentical functions in iron transport: plasma Cp drives iron transport from tissue stores while intestinal Heph facilitates iron absorption from the intestinal lumen. To clarify the function of Cp, we acutely bled Cp-/- mice to stress iron homeostasis pathways. Red cell hemoglobin recovery was defective in stressed Cp-/- mice, consistent with low iron availability. Contrary to expectations, iron was freely released from spleen and liver stores in Cp-/- mice, but intestinal iron absorption was markedly impaired. Phlebotomy of wild-type mice caused a striking shift of Cp from the duodenal epithelium to the underlying lamina propria, suggesting a critical function of Cp in basolateral iron transport. Regulated relocalization of intestinal Cp may represent a fail-safe mechanism in which Cp shares with Heph responsibility for iron absorption under stress.     

Enhanced effects of xanthohumol plus honokiol on apoptosis in 3T3-L1 adipocytes

Objective: To study the effects of xanthohumol (XN), a flavonoid found in hops (Humulus lupulus) and honokiol (HK), a lignan isolated from Magnolia officinalis, alone and in combination, on apoptotic signaling in 3T3‐L1 adipocytes. Methods and Procedures: 3T3‐L1 mature adipocytes were incubated with various concentrations of XN and HK alone and in combination. Viability and apoptosis were quantified using an MTS‐based cell viability assay and single‐stranded DNA assay, respectively. Expression of apoptosis related proteins including cleaved poly(ADP‐ribose) polymerase (PARP), cytochrome c, Bcl‐2, caspase‐3/7, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and Akt was analyzed by western blotting. Results: Combinations of XN and HK significantly decreased viability and induced apoptosis in a dose‐dependent manner and more than the additive responses to XN and HK alone. Western blot analysis showed an increase in cleaved PARP and cytochrome c release and decrease in expression of Bcl‐2 protein by XN plus HK, whereas XN and HK individually had no effect. Furthermore, the combination of XN and HK activated PTEN and inactivated Akt by decreasing levels of phosphorylated PTEN and phosphorylated Akt. Discussion: We demonstrated that although XN and HK showed little or no effect as individual compounds, in combination (XN plus HK) they showed enhanced activity in inducing apoptosis via the cytochrome c/caspase‐3/PARP and PTEN/Akt pathways in 3T3‐L1 adipocytes.     

Selection of tRNA charging quality control mechanisms that increase mistranslation of the genetic code

Mistranslation can follow two events during protein synthesis: production of non-cognate amino acid:transfer RNA (tRNA) pairs by aminoacyl-tRNA synthetases (aaRSs) and inaccurate selection of aminoacyl-tRNAs by the ribosome. Many aaRSs actively edit non-cognate amino acids, but editing mechanisms are not evolutionarily conserved, and their physiological significance remains unclear. To address the connection between aaRSs and mistranslation, the evolutionary divergence of tyrosine editing by phenylalanyl-tRNA synthetase (PheRS) was used as a model. Certain PheRSs are naturally error prone, most notably a Mycoplasma example that displayed a low level of specificity consistent with elevated mistranslation of the proteome. Mycoplasma PheRS was found to lack canonical editing activity, relying instead on discrimination against the non-cognate amino acid by kinetic proofreading. This mechanism of discrimination is inadequate for organisms where translation is more accurate, as Mycoplasma PheRS failed to support Escherichia coli growth. However, minor changes in the defunct editing domain of the Mycoplasma enzyme were sufficient to restore E. coli growth, indicating that translational accuracy is an evolutionarily selectable trait.