HYS-32-Induced Microtubule Catastrophes in Rat Astrocytes Involves the PI3K-GSK3beta Signaling Pathway.

HYS-32 is a novel derivative of combretastatin-A4 (CA-4) previously shown to induce microtubule coiling in rat primary astrocytes. In this study, we further investigated the signaling mechanism and EB1, a microtubule-associated end binding protein, involved in HYS-32-induced microtubule catastrophes. Confocal microscopy with double immunofluorescence staining revealed that EB1 accumulates at the growing microtubule plus ends, where they exhibit a bright comet-like staining pattern in control astrocytes. HYS-32 induced microtubule catastrophes in both a dose- and time-dependent manner and dramatically increased the distances between microtubule tips and the cell border. Treatment of HYS-32 (5 µM) eliminated EB1 localization at the microtubule plus ends and resulted in an extensive redistribution of EB1 to the microtubule lattice without affecting the ß-tubulin or EB1 protein expression. Time-lapse experiments with immunoprecipitation further displayed that the association between EB-1 and ß-tubulin was significantly decreased following a short-term treatment (2 h), but gradually increased in a prolonged treatment (6-24 h) with HYS-32. Further, HYS-32 treatment induced GSK3ß phosphorylation at Y216 and S9, where the ratio of GSK3ß-pY216 to GSK3ß-pS9 was first elevated followed by a decrease over time. Co-treatment of astrocytes with HYS-32 and GSK3ß inhibitor SB415286 attenuated the HYS-32-induced microtubule catastrophes and partially prevented EB1 dissociation from the plus end of microtubules. Furthermore, co-treatment with PI3K inhibitor LY294002 inhibited HYS-32-induced GSK3ß-pS9 and partially restored EB1 distribution from the microtubule lattice to plus ends. Together these findings suggest that HYS-32 induces microtubule catastrophes by preventing EB1 from targeting to microtubule plus ends through the GSK3ß signaling pathway.

HYS-32, a novel analogue of combretastatin A-4, enhances connexin43 expression and gap junction intercellular communication in rat astrocytes.

HYS-32 [4-(3,4-dimethoxyphenyl)-3-(naphthalen-2-yl)-2(5H)-furanone] is a new analogue of the anti-tumor compound combretastatin A-4 containing a cis-stilbene moiety. In this study, we investigated its effects on Cx43 gap junction intercellular communication (GJIC) and the signaling pathway involved in rat primary astrocytes. Western blot analyses showed that HYS-32 dose- and time-dependently upregulated Cx43 expression. A confocal microscopic study and scrape-loading/dye transfer analyses demonstrated that HYS-32 (5µM) induced microtubule coiling, accumulation of Cx43 in gap junction plaques, and increased GJIC in astrocytes. The HYS-32-induced microtubule coiling and Cx43 accumulation in gap junction plaques was reversed when HYS-32 was removed. Treatment of astrocytes with cycloheximide resulted in time-dependent degradation of by co-treatment with HYS-32 by increasing the half-life of Cx43. Co-treatment with HYS-32 also prevented the LPS-induced downregulation of Cx43 and inhibition of GJIC in astrocytes. HYS-32 induced activation of PKC, ERK, and JNK, and co-treatment with the PKC inhibitor Go6976 or the ERK inhibitor PD98059, but not the JNK inhibitor SP600125, prevented the HYS-32-induced increase in Cx43 expression and GJIC. Go6976 suppressed the HYS-32-induced PKC phosphorylation and increase in phospho-ERK levels, while PD98059 did not prevent the HYS-32-induced increase in phospho-PKC levels, suggesting that PKC is an upstream effector of ERK. In conclusion, our results show that HYS-32 increases the half-life of Cx43 and enhances Cx43 expression and GJIC in astrocytes via a PKC-ERK signaling cascade. These novel biological effects of HYS-32 on astrocyte gap junctions support its potential for therapeutic use as a protective agent for the central nervous system.