ABSTRACT
The aggregation of proteins into oligomers and amyloid fibrils is characteristic of several neurodegenerative diseases, including Parkinson disease (PD). In PD, the process of aggregation of α-synuclein (α-syn) from monomers, via oligomeric intermediates, into amyloid fibrils is considered the disease-causative toxic mechanism. We developed α-syn mutants that promote oligomer or fibril formation and tested the toxicity of these mutants by using a rat lentivirus system to investigate loss of dopaminergic neurons in the substantia nigra. The most severe dopaminergic loss in the substantia nigra is observed in animals with the α-syn variants that form oligomers (i.e., E57K and E35K), whereas the α-syn variants that form fibrils very quickly are less toxic. We show that α-syn oligomers are toxic in vivo and that α-syn oligomers might interact with and potentially disrupt membranes.
Subject(s)
Biopolymers/toxicity , alpha-Synuclein/toxicity , Animals , Brain/metabolism , Lentivirus/genetics , Rats , alpha-Synuclein/genetics , alpha-Synuclein/metabolismABSTRACT
The transcriptional activity of the integrated HIV provirus is dependent on the chromatin organization of the viral promoter and the transactivator Tat. Tat recruits the cellular pTEFb complex and interacts with several chromatin-modifying enzymes, including the histone acetyltransferases p300 and PCAF. Here, we examined the interaction of Tat with activation-dependent histone kinases, including the p90 ribosomal S6 kinase 2 (RSK2). Dominant-negative RSK2 and treatment with a small-molecule inhibitor of RSK2 kinase activity inhibited the transcriptional activity of Tat, indicating that RSK2 is important for Tat function. Reconstitution of RSK2 in cells from subjects with a genetic defect in RSK2 expression (Coffin-Lowry syndrome) enhanced Tat transactivation. Tat interacted with RSK2 and activated RSK2 kinase activity in cells. Both properties were lost in a mutant Tat protein (F38A) that is deficient in HIV transactivation. Our data identify a novel reciprocal regulation of Tat and RSK2 function, which might serve to induce early changes in the chromatin organization of the HIV LTR.
Subject(s)
Gene Products, tat/metabolism , HIV-1/metabolism , Ribosomal Protein S6 Kinases, 90-kDa/metabolism , Animals , Cell Line , Coffin-Lowry Syndrome/enzymology , Coffin-Lowry Syndrome/genetics , Gene Products, tat/genetics , HIV Infections/genetics , HIV-1/genetics , Histones/metabolism , Humans , Ribosomal Protein S6 Kinases, 90-kDa/genetics , Terminal Repeat Sequences/genetics , Transcriptional Activation , Virus Replication/geneticsABSTRACT
The Tat protein is a viral transactivator that activates HIV transcription through complex interactions with RNA and host cell factors. Tat undergoes multiple posttranslational modifications that regulate the dynamics and complexity of these interactions. The biology of these modifications and their role in Tat function are reviewed.