There is no proof that the HN cDNA represents a gene, that its origin is nuclear, or that the HN peptide is produced in vivo. The information that the long HN cDNA sequence is virtually identical to mitochondrial rRNA should have been put in the Discussion rather than published as supplementary material. The Discussion should have contained the following:The long cDNA [1,567 bp including a poly(A) tail] containing the HN ORF is Ͼ99% identical (1548͞1552) to positions 1679-3230 of mitochondrial DNA (GenBank accession no. AB055387). Because mitochondrial DNA positions 1667-3224 code for mitochondrial 16S rRNA, and mitochondrial 16S rRNA has a short poly(A) tail during transcription (1), the virtual identity of the long HN cDNA to mitochondrial DNA indicates that HN cDNA is mitochondrial 16S rRNA with a poly(A) tail. This makes it unlikely that the peptide encoded by the ORF in HN cDNA is naturally produced. Further, the 75-bp HN ORF is separated from the 5Ј end of the long HN cDNA by a 950-bp region containing at least seven ORFs, each with a stop codon. This makes it even more unlikely that HN peptide is produced from the long HN cDNA. It should also be noted that mitochondria-like nuclear sequences occur commonly as pseudogenes (2). Finally, the HN peptide lacks the characteristic N-terminal signal sequence of secreted peptides, although we suggest that a signal peptide-like function may be encoded in the primary sequence of HN peptide. For all of these reasons, it is unlikely that the HN ORF leads to production of the predicted peptide in vivo.Nonetheless, it remains possible that HN cDNA represents a nuclear transcribed mRNA and that the HN peptide is a natural product. Long regions of the HN cDNA are Ͼ99% identical to certain registered human mRNAs [1545͞1553 at positions 14-1580 of FLJ22981 fis cDNA (AK026634), 925͞929 at positions 1-929 of FLJ22517 fis cDNA, 914͞919 at positions 1348-2266 of FLJ20341 fis cDNA, and 345͞346 at positions 1-346 of PNAS-32 mRNA]. PNAS-32 mRNA is actually expressed to produce NB4 apoptosis-related protein, showing that this mRNA is transcribed from a nuclear gene. In addition, HN cDNA is highly similar to regions of more than 1,000 bp on human chromosomes [positions 245364-244075 of chromosome 11 draft sequence (92%, 1198͞1290), positions 65752-66775 of chromosome X draft sequence (95%, 974͞1025), and positions 687598-688608 of chromosome 5 draft sequence (93%, 954͞1016)]. Also, the HN ORF has a Kozak-like sequence, although it is not canonical.

A novel factor, termed Humanin (HN), antagonizes against neurotoxicity by various types of familial Alzheimer's disease (AD) genes [V642I and K595N/M596L (NL) mutants of amyloid precursor protein (APP), M146L-presenilin (PS) 1, and N141I-PS2] and by A␤1-43 with clear action specificity ineffective on neurotoxicity by polyglutamine repeat Q79 or superoxide dismutase 1 mutants. Here we report that HN can also inhibit neurotoxicity by other AD-relevant insults: other familial AD genes (A617G-APP, L648P-APP, A246E-PS1, L286V-PS1, C410Y-PS1, and H163R-PS1), APP stimulation by anti-APP antibody, and other A␤ peptides (A␤1-42 and A␤25-35). The action specificity was further indicated by the finding that HN could not suppress neurotoxicity by glutamate or prion fragment. Against the AD-relevant insults, essential roles of Cys 8 and Ser 14 were commonly indicated, and the domain from Pro 3 to Pro 19 was responsible for the rescue action of HN, in which seven residues turned out to be essential. We also compared the neuroprotective action of S14G HN (HNG) with that of activity-dependent neurotrophic factor, IGF-I, or basic FGF for the antagonism against various AD-relevant insults (V642I-APP, NL-APP, M146L-PS1, N141I-PS2, and A␤1-43). Although all of these factors could abolish neurotoxicity by A␤1-43, only HNG could abolish cytotoxicities by all of them. HN and HN derivative peptides may provide a new insight into the study of AD pathophysiology and allow new avenues for the development of therapeutic interventions for various forms of AD.

Here we investigated whether the sensitivity of microtubules to severing by katanin is regulated by acetylation of the microtubules. During interphase, fibroblasts display long microtubules with discrete regions rich in acetylated tubulin. Overexpression of katanin for short periods of time produced breaks preferentially in these regions. In fibroblasts with experimentally enhanced or diminished microtubule acetylation, the sensitivity of the microtubules to severing by katanin was increased or decreased, respectively. In neurons, microtubules are notably more acetylated in axons than in dendrites. Experimental manipulation of microtubule acetylation in neurons yielded similar results on dendrites as observed on fibroblasts. However, under these experimental conditions, axonal microtubules were not appreciably altered with regard to their sensitivity to katanin. We hypothesized that this may be attributable to the effects of tau on the axonal microtubules, and this was validated by studies in which overexpression of tau caused microtubules in dendrites and fibroblasts to be more resistant to severing by katanin in a manner that was not dependent on the acetylation state of the microtubules. Interestingly, none of these various findings apply to spastin, because the severing of microtubules by spastin does not appear to be strongly influenced by either the acetylation state of the microtubules or tau. We conclude that sensitivity to microtubule severing by katanin is regulated by a balance of factors, including the acetylation state of the microtubules and the binding of tau to the microtubules. In the neuron, this contributes to regional differences in the microtubule arrays of axons and dendrites.

It is commonly stated that microtubules gradually disintegrate as tau becomes dissociated from them in tauopathies such as Alzheimer's disease. However, there has been no compelling evidence to date that such disintegration is due to depolymerization of microtubules from their ends. In recent studies, we have shown that neurons contain sufficient levels of the microtubule-severing protein termed katanin to completely break down the axonal microtubule array if not somehow attenuated. The presence of tau on axonal microtubules renders them notably less sensitive to katanin, prompting us to posit that microtubule disintegration in tauopathies may result from elevated severing of the microtubules as they lose tau. In support of this hypothesis, we demonstrate here that pathogenic tau mutants that bind less strongly to microtubules than wild-type tau provide correspondingly less protection against katanin-based severing. Using cultured rat hippocampal neurons, we pursued two potential therapies for fortifying axonal microtubules against excess severing by katanin, under conditions of tau depletion. We found that either deacetylating the microtubules via overexpression of HDAC6 or treating the neurons with NAP, a microtubule-interacting neuroprotective peptide, resulted in notable protection of the microtubules against katanin-based loss. In both cases, we found that these treatments also diminished the characteristic increase in axonal branching that normally accompanies tau depletion, an effect that is also known to be directly related to the severing of microtubules. These observations may be useful in developing therapeutic regimes for preserving microtubules against loss in the axons of patients suffering from tauopathies.

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Prostate cancer is one of the most common cancers in men, with more than 500,000 new worldwide cases reported annually, resulting in 200,000 deaths of mainly older men in developed countries. Existing treatments have not proved very effective in managing prostate cancer, and continuing efforts therefore are ongoing to explore novel targets and strategies for future therapies. LAPSER1 has been identified as a candidate tumor suppressor gene in prostate cancer, but its true functions remain unknown. We report here that LAPSER1 colocalizes to the centrosomes and midbodies in mitotic cells with gamma-tubulin, MKLP1, and p80 katanin, and is involved in cytokinesis. Moreover, RNAi-mediated disruption of LAPSER1, which is accompanied by the mislocalization of p80 katanin, results in malformation of the central spindle. Significantly, the enhanced expression of LAPSER1 induces binucleation and renders the cells resistant to oncogenic transformation. In cells transformed by the v-Fps oncogene, overexpressed LAPSER1 induces abortive cytokinesis, followed by mitotic catastrophe in a p80 katanin-dependent manner. Cells that are rescued from this apoptotic pathway with Z-VAD-fmk display karyokinesis. These results suggest that LAPSER1 participates in cytokinesis by interacting with p80 katanin, the disruption of which may potentially cause genetic instability and cancer.

The microtubule associated-protein tau has been identified as an effective positive prognostic indicator in breast cancer. To explore the physiological function of tau in early carcinogenesis, endogenous tau was knocked down in primary cultured human mammary epithelial cells. This resulted in chromosome-bridging during anaphase followed by micronucleation, both of which were suppressed by a further katanin-like1 knockdown. We also detected that the exogenously expressed katanin-like1 induction of cellular transformation is prevented by exogenous tau in rat fibroblasts. The mutant katanin-like1 (L123V) identified in breast cancer showed an increase in this transformation capacity as well as microtubule severing activity resistant to tau. The tau knockdown resulted in a loss of the kinetochore fibers on which tau is normally localized. This physical fragility was also observed in isolated tau-knockdown mitotic spindles, supporting the relevance of microtubule damage to the onset of transformation. The karyotyping of tau-knockdown cells showed increased frequency of loss of one X chromosome, further suggesting the involvement of tau in breast tumorigenesis. We propose that tau may contribute to tumor progression by protecting spindle microtubules from excess severing by katanin-like1. We also present data indicating that the microtubule-binding octapeptide NAP is a candidate modifier against the tau deficiency in tumor cells.