Non-Secreted Clusterin Isoforms Are Translated in Rare Amounts from Distinct Human mRNA Variants and Do Not Affect Bax-Mediated Apoptosis or the NF-κB Signaling Pathway
Open Access
- 20 September 2013
- journal article
- research article
- Published by Public Library of Science (PLoS) in PLOS ONE
- Vol. 8 (9), e75303
- https://doi.org/10.1371/journal.pone.0075303
Abstract
Clusterin, also known as apolipoprotein J, is expressed from a variety of tissues and implicated in pathological disorders such as neurodegenerative diseases, ischemia and cancer. In contrast to secretory clusterin (sCLU), which acts as an extracellular chaperone, the synthesis, subcellular localization and function(s) of intracellular CLU isoforms is currently a matter of intense discussion. By investigating human CLU mRNAs we here unravel mechanisms leading to the synthesis of distinct CLU protein isoforms and analyze their subcellular localization and their impact on apoptosis and on NF-κB-activity. Quantitative PCR-analyses revealed the expression of four different stress-inducible CLU mRNA variants in non-cancer and cancer cell lines. In all cell lines variant 1 represents the most abundant mRNA, whereas all other variants collectively account for no more than 0.34% of total CLU mRNA, even under stressed conditions. Overexpression of CLU cDNAs combined with in vitro mutagenesis revealed distinct translational start sites including a so far uncharacterized non-canonical CUG start codon. We show that all exon 2-containing mRNAs encode sCLU and at least three non-glycosylated intracellular isoforms, CLU1‑449, CLU21‑449 and CLU34‑449, which all reside in the cytosol of unstressed and stressed HEK‑293 cells. The latter is the only form expressed from an alternatively spliced mRNA variant lacking exon 2. Functional analysis revealed that none of these cytosolic CLU forms modulate caspase-mediated intrinsic apoptosis or significantly affects TNF-α-induced NF-κB-activity. Therefore our data challenge some of the current ideas regarding the physiological functions of CLU isoforms in pathologies.Keywords
This publication has 72 references indexed in Scilit:
- CRM1 Protein-mediated Regulation of Nuclear Clusterin (nCLU), an Ionizing Radiation-stimulated, Bax-dependent Pro-death FactorJournal of Biological Chemistry, 2011
- mda‐7/IL‐24 differentially regulates soluble and nuclear clusterin in prostate cancerJournal of Cellular Physiology, 2011
- Targeting the Cytoprotective Chaperone, Clusterin, for Treatment of Advanced CancerClinical Cancer Research, 2010
- Clusterin Facilitates COMMD1 and I-κB Degradation to Enhance NF-κB Activity in Prostate Cancer CellsMolecular Cancer Research, 2010
- Cellular stress and RNA splicingTrends in Biochemical Sciences, 2009
- Advances and Challenges in Basic and Translational Research on ClusterinCancer Research, 2009
- Regulation of CLU Gene Expression by Oncogenes and Epigenetic FactorsPublished by Elsevier BV ,2009
- Transport Pathways for Clearance of Human Alzheimer's Amyloid β-Peptide and Apolipoproteins E and J in the Mouse Central Nervous SystemJournal of Cerebral Blood Flow & Metabolism, 2006
- Clusterin inhibits apoptosis by interacting with activated BaxNature, 2005
- Block of HAC1 mRNA Translation by Long-Range Base Pairing Is Released by Cytoplasmic Splicing upon Induction of the Unfolded Protein ResponseCell, 2001