The small heat shock protein alphaB-crystallin (cryAB) is known to be upregulated in various tissues under inflammatory, traumatic injury, stress and some disease conditions. In the human brain, cryAB is expressed by glial cells - astrocytes & oligodendrocytes. In Glioblastoma Multiforme (GBM- a highly aggressive primary brain tumor involving astrocytes) and some other inflammation driven neurodegenerative disorders, the level of cryAB in astrocytes is increased.
Since cryAB expression is known to be upregulated by astrocytes in various neurodegenerative disorders and since cryAB has been shown to be present extracellularly, in cerebrospinal fluid, it was postulated that astrocytes secrete cryAB into the extracellular milieu. The data presented here shows that astrocytes secrete exosomes and cryAB is one of the cargo proteins carried in exosomes. Additionally, following stimulation with oxidative stress and inflammatory cytokines, interleukin-1beta (IL-1β) and tumor necrosis factor alpha (TNF-α), the cryAB levels in astrocytes and its secretion via exosomes is significantly increased.
CryAB has no signal sequences and thus the mechanisms governing targeting of cryAB for exosomal secretion was not known. Based on available literature, it was hypothesized that post translational modifications (PTMs) of cryAB regulate its packaging and secretion via exosomes. Among the PTMs which govern cryAB’s activity and function are phosphorylation at three serine residues viz. Ser19, Ser45 and Ser59. This study finds that the majority of exosomal cryAB is nonphosphorylated. Mimicking phosphorylation alters cellular distribution of cryAB forming cytosolic inclusions and negatively regulates its exosomal secretion. Additionally, O-GlcNAcylation of cryAB is an essential modification required for its secretion via exosomes.
The data presented provides insight into the mechanisms governing packaging of some of the proteins into vesicles which constitute the exosomal secretory pathway.
|Advisor:||Abraham, Edathara C.|
|Commitee:||Baldini, Giulia, Diekman, Alan B., Kaushal, Gur P., Tackett, Alan J.|
|School:||University of Arkansas for Medical Sciences|
|Department:||Biochemistry and Molecular Biology|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 77/11(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Cellular biology, Biochemistry|
|Keywords:||Alphab crystallin, Exosomes, Glioblastoma multiforme, O-linked glycosylation, Phosphorylation, Protein post translational modifications|
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