The tyrosine kinase v-Src modifies cytotoxicities of anticancer drugs targeting cell division.

v-Src oncogene causes cell transformation through its strong tyrosine kinase activity. We have revealed that v-Src-mediated cell transformation occurs at a low frequency and it is attributed to mitotic abnormalities-mediated chromosome instability. v-Src directly phosphorylates Tyr-15 of cyclin-dependent kinase 1 (CDK1), thereby causing mitotic slippage and reduction in Eg5 inhibitor cytotoxicity. However, it is not clear whether v-Src modifies cytotoxicities of the other anticancer drugs targeting cell division. In this study, we found that v-Src restores cancer cell viability reduced by various microtubule-targeting agents (MTAs), although v-Src does not alter cytotoxicity of DNA-damaging anticancer drugs. v-Src causes mitotic slippage of MTAs-treated cells, consequently generating proliferating tetraploid cells. We further demonstrate that v-Src also restores cell viability reduced by a polo-like kinase 1 (PLK1) inhibitor. Interestingly, treatment with Aurora kinase inhibitor strongly induces cell death when cells express v-Src. These results suggest that the v-Src modifies cytotoxicities of anticancer drugs targeting cell division. Highly activated Src-induced resistance to MTAs through mitotic slippage might have a risk to enhance the malignancy of cancer cells through the increase in chromosome instability upon chemotherapy using MTAs.

Hsp105α suppresses Adriamycin-induced cell death via nuclear localization signal-dependent nuclear accumulation.

Heat shock protein 105 (Hsp105) is a molecular chaperone, and the isoforms Hsp105α and Hsp105ß exhibit distinct functions with different subcellular localizations. Hsp105ß localizes in the nucleus and induces the expression of the major heat shock protein Hsp70, whereas cytoplasmic Hsp105α is less effective in inducing Hsp70 expression. Hsp105 shuttles between the cytoplasm and the nucleus; the subcellular localization is governed by the relative activities of the nuclear localization signal (NLS) and nuclear export signal (NES). Here, we show that nuclear accumulation of Hsp105α but not Hsp105ß is involved in Adriamycin (ADR) sensitivity. Knockdown of Hsp105α induces cell death at low ADR concentration, at which ADR is less effective in inducing cell death in the presence of Hsp105α. Of note, Hsp105 is localized in the nucleus under these conditions, even though Hsp105ß is not expressed, indicating that Hsp105α accumulates in the nucleus in response to ADR treatment. The exogenously expressed Hsp105α but not its NLS mutant localizes in the nucleus of ADR-treated cells. In addition, the expression level of the nuclear export protein chromosomal maintenance 1 (CRM1) was decreased by ADR treatment of cells, and CRM1 knockdown caused nuclear accumulation of Hsp105α both in the presence and absence of ADR. These results indicating that Hsp105α accumulates in the nucleus in a manner dependent on the NLS activity via the suppression of nuclear export. Our findings suggest a role of nuclear Hsp105α in the sensitivity against DNA-damaging agents in tumor cells.

Inhibitors of the VEGF Receptor Suppress HeLa S3 Cell Proliferation via Misalignment of Chromosomes and Rotation of the Mitotic Spindle, Causing a Delay in M-Phase Progression.

Cell division is the process by which replicated chromosomes are separated into two daughter cells. Although regulation of M phase has been extensively investigated, not all regulating factors have been identified. Over the course of our research, small molecules were screened to identify those that regulate M phase. In the present study, the vascular endothelial growth factor receptor (VEGFR) inhibitors A83-01, SU4312, and Ki8751 were examined to determine their effects on M phase. Treatment of HeLa S3 cells with these inhibitors suppressed cell proliferation in a concentration-dependent manner, and also suppressed Akt phosphorylation at Ser473, a marker of Akt activation. Interestingly, cleaved caspase-3 was detected in Adriamycin-treated cells but not in inhibitor-treated cells, suggesting that these inhibitors do not suppress cell proliferation by causing apoptosis. A cell cycle synchronization experiment showed that these inhibitors delayed M phase progression, whereas immunofluorescence staining and time-lapse imaging revealed that the M phase delay was accompanied by misalignment of chromosomes and rotation of the mitotic spindle. Treatment with the Mps1 inhibitor AZ3146 prevented the SU4312-induced M phase delay. In conclusion, the VEGFR inhibitors investigated here suppress cell proliferation by spindle assembly checkpoint-induced M phase delay, via misalignment of chromosomes and rotation of the mitotic spindle.