Nuclear and cytoplasmic tau proteins from human nonneuronal cells share common structural and functional features with brain tau

Abstract

The heterogeneous family of tau proteins interacts with microtubules, actin filaments, and intermediate filaments. The tau isoforms have been shown to play a major role in neuronal polarity. However, tau-like proteins have been found in several other types of cells. Previous studies have also indicated the presence of a nuclear tau. The relationships between nuclear and cytoplasmic tau as well as the functional aspects of the nuclear tau are unknown. In this study, we demonstrate by reverse transcriptase polymerase chain reaction using specific primers that a transcript with features of neuronal tau is present in human fibroblast and Huh-7 hepatoma cell lines. Additionally, we present the first isolation and characterization of cytosolic and nuclear tau-like proteins from nonneuronal cells. Nonneuronal cytosolic tau components were isolated using the perchloric acid precipitation approach, while nuclear tau was isolated after selective extractions using high-ionic strength buffers. The cytoplasmic tau of nonneuronal cells is composed of at least three isoforms, whereas two main isoforms were detected in nuclear tau. Interestingly, the cytoplasmic and nuclear tau components exhibited the capacity to promote tubulin polymerization in vitro. Immunofluorescence studies using monoclonal anti-tau antibodies indicated a discrete distribution of tau protein in both the interphase and mitotic nucleus. In the latter, tau colocalized with the chromosomal scaffold. These studies, together with previous evidence on tau roles in modulating microtubule growth from centrosomes, and its role in the interaction patterns that stabilize the integrity of the cytoskeletal network, strongly support the idea that tau is a multifunctional protein involved in fundamental cellular processes.

Pseudomonas aeruginosa exoenzymes U and Y induce a transmissible endothelial proteinopathy

“…Neuronal and nonneuronal forms of tau are described elsewhere (11,66), although expression of an endothelial cell tau is not widely acknowledged. Our previous studies using P. aeruginosa ExoY indicate that it induces a microtubule-dependent permeability defect.…”

Tau protein binds to pericentromeric DNA: a putative role for nuclear tau in nucleolar organization

“…Some tau species have also been described associated with chromatin fractions (Greenwood and Johnson, 1995), or interacting with the plasma membrane (Brandt et al, 1995) and with the non-receptor tyrosine kinase Fyn . Even though tau is present mainly in neuronal cells, it has also been observed in non-neuronal cells, with a nucleolar localization in HeLa cells, non-transformed human fibroblasts and lymphoblasts (Thurston et al, 1996), as well as in human Huh-7 hepatoma cells (Cross et al, 2000). In all these non-neuronal cell types several isoforms of tau were detected with Tau-1 and Tau-5 antibodies.…”

“…Ultrastructural localization studies identified tau associated with ribosomes and somatodendritic compartments in certain areas of the central nervous system (Papasozomenos and Su, 1991). More recently, another non-microtubular localization of tau was identified in the nucleus of neuronal and non-neuronal cells (Lu and Wood, 1993;Lambert et al, 1995;Thurston et al, 1996;Cross et al, 2000). Some tau species have also been described associated with chromatin fractions (Greenwood and Johnson, 1995), or interacting with the plasma membrane (Brandt et al, 1995) and with the non-receptor tyrosine kinase Fyn .…”

Visualizing the microtubule-associated protein tau in the nucleus

“…It was speculated that the nucleus might contain factors that are capable of inducing PHF formation, and when these nuclear PHFs are released into the cytoplasm that they would act as a catalyzer of tau aggregation and subsequent neurodegeneration. A nuclear role for tau was extended to human non-neuronal cells, demonstrating shared structural and functional features of nuclear and cytoplasmic tau [10]. Tau is a phosphoprotein, with hyperphosphorylation causing its aggregation [11].…”

“…Preparations were counterstained with DAPI before mounting with mounting medium (Dako). Method II [10]. After washing with PBS, the cells were fixed with pre-cooled methanol at 20°C for 15 min.…”