A NOVEL TAU-TRANSCRIPT IN CULTURED HUMAN NEUROBLASTOMA-CELLS EXPRESSING NUCLEAR-TAU

We previously reported the presence of the microtubule-associated prot ein, 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 t au. Northern blot analysis of poly A+ mRNA detects a novel 2-kb tau tr anscript 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, actinom ycin D transcription inhibition experiments indicate that the 2-kb mes sage is not derived from the 6-kb message, but instead arises from the original tau transcript. One of the human neuroblastoma cell lines ex amined contains both nuclear and cytoplasmic tau as assayed by both We stern 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. Immunofluoresc ence analysis of this cell line demonstrates that the cytoplasmic tau is not localized to microtubules. Together, these results indicate tha t the 2-kb tau message in humans may specify tau for non-microtubule f unctions in both the cytoplasm and the nucleus. We hypothesize that th is is accomplished via a message targeting mechanism mediated by the u ntranslated regions of the tau messages.