No abstract

The conserved RNA binding protein La recognizes UUU-3OH on its small nuclear RNA ligands and stabilizes them against 3-end-mediated decay. We report that newly described La-related protein 4 (LARP4) is a factor that can bind poly(A) RNA and interact with poly(A) binding protein (PABP). Yeast two-hybrid analysis and reciprocal immunoprecipitations (IPs) from HeLa cells revealed that LARP4 interacts with RACK1, a 40S ribosome-and mRNA-associated protein. LARP4 cosediments with 40S ribosome subunits and polyribosomes, and its knockdown decreases translation. Mutagenesis of the RNA binding or PABP interaction motifs decrease LARP4 association with polysomes. Several translation and mRNA metabolism-related proteins use a PAM2 sequence containing a critical invariant phenylalanine to make direct contact with the MLLE domain of PABP, and their competition for the MLLE is thought to regulate mRNA homeostasis. Unlike all ϳ150 previously analyzed PAM2 sequences, LARP4 contains a variant PAM2 (PAM2w) with tryptophan in place of the phenylalanine. Binding and nuclear magnetic resonance (NMR) studies have shown that a peptide representing LARP4 PAM2w interacts with the MLLE of PABP within the affinity range measured for other PAM2 motif peptides. A cocrystal of PABC bound to LARP4 PAM2w shows tryptophan in the pocket in PABC-MLLE otherwise occupied by phenylalanine. We present evidence that LARP4 expression stimulates luciferase reporter activity by promoting mRNA stability, as shown by mRNA decay analysis of luciferase and cellular mRNAs. We propose that LARP4 activity is integrated with other PAM2 protein activities by PABP as part of mRNA homeostasis.The RNA binding domain of the conserved La protein consists of a La motif (LaM) and an RNA recognition motif (RRM) that work together to recognize UUU-3ЈOH on small nascent transcripts and to protect them from 3Ј exonucleases (7,45). In addition to this, La proteins can modulate mRNA translation (30,(63)(64)(65). The LaM-RRM arrangement has been found in La-related proteins 1 (LARP1), 1b, 4, 4b, 6, and 7, which have been separately conserved during evolution (8, 10) (LARP4b is also referred to as LARP5 in multiple databases and here will be designated LARP5/4b). LARP7 is specific for 7SK snRNA, which it recognizes in part via UUU-3ЈOH (29, 46). LARP6 binds to a stem-loop in the 5Ј untranslated regions (UTRs) of collagen mRNAs in a uracil-dependent manner (15), and LARP1 was shown to bind poly(U) and to a lesser extent poly(G), but not poly(A) or poly(C) (51). Consistent with these specificities, LARP1, -6, and -7 have conserved all of the amino acids involved in UUU-3ЈOH recognition in La-RNA crystals (37, 66), while LARP4 and -5/4b have diverged, suggesting alternative RNA binding (8). Moreover, an invariant divergence in all of the LARP4 and -5/4b sequences available occurs in a most critical residue involved in base-specific recognition seen in La-RNA crystals, corresponding to human La Q20, suggesting a conserved difference in RNA recognition (8). Although the LaM-RRM in ...

Ligands of the translocator protein (TSPO) elicit pleiotropic neuroprotective effects that represent emerging treatment strategies for several neurodegenerative conditions. To investigate the potential of TSPO as a therapeutic target for Alzheimer's disease (AD), the current study assessed the effects of the TSPO ligand Ro5-4864 on the development of neuropathology in 3xTgAD mice. The effects of the TSPO ligand on neurosteroidogenesis and AD-related neuropathology including β-amyloid accumulation, gliosis and behavioral impairment were examined under both early intervention (7 month-old young-adult male mice with low pathology) and treatment (24 month-old, aged male mice with advanced neuropathology) conditions. Ro5-4864 treatment not only effectively attenuated development of neuropathology and behavioral impairment in young adult mice, but also reversed these indices in aged 3xTgAD mice. Reduced levels of soluble β-amyloid were also observed by the combination of TSPO ligands Ro5-4864 and PK11195 in non-transgenic mice. These findings suggest TSPO is a promising target for the development of pleiotropic treatment strategies for the management of AD.

In obesity, dysregulation of adipocytokines is involved in several pathological conditions including diabetes and certain cancers. As a member of the adipocytokines, adiponectin plays crucial roles in whole-body energy homeostasis. Recently, it has been reported that the level of plasma adiponectin is reduced in several types of cancer patients. However, it is largely unknown whether and how adiponectin affects colon cancer cell growth. Here, we show that adiponectin suppresses the proliferation of colon cancer cells including HCT116, HT29, and LoVo. In colon cancer cells, adiponectin attenuated cell cycle progression at the G(1)/S boundary and concurrently increased expression of cyclin-dependent kinase inhibitors such as p21 and p27. Adiponectin stimulated AMP-activated protein kinase (AMPK) phosphorylation whereas inhibition of AMPK activity blunted the effect of adiponectin on the proliferation of colon cancer cells. Furthermore, knockdown of adiponectin receptors such as AdipoR1 and AdipoR2 relieved the suppressive effect of adiponectin on the growth of colon cancer cells. In addition, adiponectin repressed the expression of sterol regulatory element binding protein-1c, which is a key lipogenic transcription factor associated with colon cancers. These results suggest that adiponectin could inhibit the growth of colon cancer cells through stimulating AMPK activity.