Cell-based chemical fingerprinting identifies telomeres and lamin A as modifiers of DNA damage response in cancer cells.

Telomere maintenance by telomerase activity supports the infinite growth of cancer cells. MST-312, a synthetic telomerase inhibitor, gradually shortens telomeres at non-acute lethal doses and eventually induces senescence and apoptosis of telomerase-positive cancer cells. Here we report that MST-312 at higher doses works as a dual inhibitor of telomerase and DNA topoisomerase II and exhibits acute anti-proliferative effects on cancer cells and xenografted tumours in vivo. Our cell-based chemical fingerprinting approach revealed that cancer cells with shorter telomeres and lower expression of lamin A, a nuclear architectural protein, exhibited higher sensitivity to the acute deleterious effects of MST-312, accompanied by formation of telomere dysfunction-induced foci and DNA double-strand breaks. Telomere elongation and lamin A overexpression attenuated telomeric and non-telomeric DNA damage, respectively, and both conferred resistance to apoptosis induced by MST-312 and other DNA damaging anticancer agents. These observations suggest that sufficient pools of telomeres and a nuclear lamina component contribute to the cellular robustness against DNA damage induced by therapeutic treatment in human cancer cells.

RSK1 protects P-glycoprotein/ABCB1 against ubiquitin-proteasomal degradation by downregulating the ubiquitin-conjugating enzyme E2 R1.

P-glycoprotein (P-gp) is a critical determinant of multidrug resistance in cancer. We previously reported that MAPK inhibition downregulates P-gp expression and that P-gp undergoes ubiquitin-proteasomal degradation regulated by UBE2R1 and SCFFbx15. Here, we investigated the crosstalk between MAPK inhibition and the ubiquitin-proteasomal degradation of P-gp. Proteasome inhibitors or knockdown of FBXO15 and/or UBE2R1 cancelled MEK inhibitor-induced P-gp downregulation. RSK1 phosphorylated Thr162 on UBE2R1 but did not phosphorylate FBXO15. MEK and RSK inhibitors increased UBE2R1-WT but not UBE2R1-T162D and -T162A expression. UBE2R1-T162D showed higher self-ubiquitination and destabilisation than UBE2R1-WT and -T162A. Unlike UBE2R1-WT and -T162A, UBE2R1-T162D did not induce P-gp ubiquitination. UBE2R1-WT or -T162A downregulated P-gp expression and upregulated rhodamine 123 level and sensitivity to vincristine and doxorubicin. However, UBE2R1-T162D did not confer any change in P-gp expression, rhodamine 123 accumulation and sensitivity to the drugs. These results suggest that RSK1 protects P-gp against ubiquitination by reducing UBE2R1 stability.

[Anesthetic management of MIDCAB with high dose diltiazem].

Precise management of blood pressure and heart rate is required during minimally invasive direct coronary artery bypass (MIDCAB). Previously, low dose diltiazem and beta-blokers have been employed for control of circulation during this procedure, but we report 2 patients whose blood pressure and heart rate were managed during MIDCAB by high-dose diltiazem. In both patients, anesthesia was induced with propofol, vecuronium and fentanyl, and maintained by continuous infusion of propofol and inhalation of oxygen and nitrous oxide. Fentanyl, midazolam, and sevoflurane were administered occasionally. Immediately after the induction, a continuous infusion of nicorandil (2 to 4 mg.hr-1) was started and diltiazem (4 to 15 micrograms.kg-1.min-1) was administered continuously from the beginning of the surgery. Following discontinuation of diltiazem administration, blood pressure and heart rate returned to their preoperative values. These results suggest that safe anesthetic management during MIDCAB can be performed with highdose diltiazem.