A novel tau transcript in cultured human neuroblastoma cells expressing nuclear tau.

Abstract

Abstract. We previously reported the presence of the microtubule-associated protein, tau in the nuclei of primate cells in culture. The present study confirms the existence of nuclear tau in two human neuroblastoma cells lines by indirect immunofluorescence and Western blot using mAbs to tau. Northern blot analysis of poly A ÷ mRNA detects a novel 2-kb tau transcript coexpressed with the 6-kb message in cultured human cells and human frontal cortex. PCR and cDNA sequencing demonstrate that the 2-kb message contains the entire tau coding region. Furthermore, actinomycin D transcription inhibition experiments indicate that the 2-kb message is not derived from the 6-kb message, but instead arises from the original tau transcript. One of the human neuroblastoma cell lines examined contains both nuclear and cytoplasmic tau as assayed by both Western blot and indirect immunofluorescence. Northern blot analysis of this cell line indicates that copious amounts of the 2-kb message are present while little of the 6-kb transcript is obvious. Immunofluorescence analysis of this cell line demonstrates that the cytoplasmic tau is not localized to microtubules. Together, these results indicate that the 2-kb tau message in humans may specify tau for nonmicrotubule functions in both the cytoplasm and the nucleus. We hypothesize that this is accomplished via a message targeting mechanism mediated by the untranslated regions of the tau messages.

Tau could protect DNA double helix structure

“…Subsequent studies have shown the presence of tau in nuclei of neuronal cell lines [5][6][7][8][9][10]32], and the binding of tau to both eukaryotic DNA and phage DNA [9]. However, the function of tau in the neuronal nuclei has been unknown.…”

“…In addition to its association with microtubules, a major location, tau has been found to be associated with ribosomes [3,4] and has been shown to be localized in nuclei of human neuroblastoma cells, human cervical carcinoma, human macrophages, monkey kidney and PC12 cells [5][6][7]. Its localization has been observed at the nucleolar regions of the acrocentric chromosomes of human neuroblastoma cells, associated with both fibrillar regions of interphase nucleoli and the nucleolar organizer regions [5,8]. Microtubule-associated proteins have been shown to have a higher affinity to DNA than to microtubules and their removal from the microtubules by DNA causes microtubule breakdown [9].…”

Tau protein binds single‐stranded DNA sequence specifically – the proof obtained in vitro with non‐equilibrium capillary electrophoresis of equilibrium mixtures

“…A number of studies with different cell types demonstrated that tau proteins could be found in nuclei in a complex with nuclear DNA [6,[21][22][23][24]. Iqbal and co-workers [12] reported that by binding dsDNA tau increases its melting temperature.…”

Visualizing the microtubule-associated protein tau in the nucleus

“…One cell line (CG) failed to reveal cytoplasmic tau, and tau was only observed in the nuclear FA fraction, while a second cell line (JC) revealed tau in both the soluble and FA fraction [5]. Cytoplasmic tau was shown not to localize to microtubules [8].…”

“…When analyzing nuclear tau, human cell lines (JC, CG, LA-N-5, HeLa, and SH-SY5Y) consistently showed nucleolar Tau as detected with the Tau-1 antibody, while a rodent neuroblastoma cell line (N2a) consistently failed to do so [5,7,8]. Two human cell lines (JC and CG) were further analyzed by subcellular fractionation followed by formic acid (FA) extraction to enrich for insoluble proteins.…”