No abstract

Neurite growth requires two guanine nucleotide-binding protein polymers of tubulins and septins. However, whether and how those cytoskeletal systems are coordinated was unknown. Here we show that the acute knockdown or knockout of the pivotal septin subunit SEPT7 from cerebrocortical neurons impairs their interhemispheric and cerebrospinal axon projections and dendritogenesis in perinatal mice, when the microtubules are severely hyperacetylated. The resulting hyperstabilization and growth retardation of microtubules are demonstrated in vitro. The phenotypic similarity between SEPT7 depletion and the pharmacological inhibition of α-tubulin deacetylase HDAC6 reveals that HDAC6 requires SEPT7 not for its enzymatic activity, but to associate with acetylated α-tubulin. These and other findings indicate that septins provide a physical scaffold for HDAC6 to achieve efficient microtubule deacetylation, thereby negatively regulating microtubule stability to an optimal level for neuritogenesis. Our findings shed light on the mechanisms underlying the HDAC6-mediated coupling of the two ubiquitous cytoskeletal systems during neural development.

We examined the mechanism by which estrogen regulates telomerase activity in Caov-3 human ovarian cancer cell lines, which express ER, to determine whether the regulation affects the expression and/or phosphorylation of the telomerase catalytic subunit (hTERT). 17b-Estradiol (E 2 ) induced telomerase activity and hTERT expression. Transient expression assays using luciferase reporter plasmids containing various fragments of hTERT promoter showed that the estrogen-responsive element appeared to be partially responsible for the E 2 -induced activation of the hTERT promoter. Either pretreatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, or transfection with a dominantnegative Akt attenuated the E 2 -induced activation of the hTERT promoter. In addition, estrogen induced the phosphorylation of IjB inhibitor protein via the Akt cascade, and cotransfection with a dominant-negative subunit of NFjB attenuated the response of the ERE-deleted hTERT promoter to E 2 . Moreover, E 2 induced the phosphorylation of hTERT, the association of 14-3-3 protein and NFjB with hTERT, and nuclear accumulation of hTERT in an Akt-dependent manner. These results indicate that E 2 induces telomerase activity not only by transcriptional regulation of hTERT via an ERE-dependent mechanism and a PI3K/Akt/NFjB cascade, but also by post-transcriptional regulation via Akt-dependent phosphorylation of hTERT. Thus, the phosphorylation of Akt is a key event in the induction of telomerase activity by E 2 in human ovarian cancer cells.