5-Flurouracil disrupts nuclear export and nuclear pore permeability in a calcium dependent manner

Abstract

Regulation of nuclear transport is an essential component of apoptosis. As chemotherapy induced cell death progresses, nuclear transport and the nuclear pore complex (NPC) are slowly disrupted and dismantled. 5-Fluorouracil (5-FU) and the camptothecin derivatives irinotecan and topotecan, are linked to altered nuclear transport of specific proteins; however, their general effects on the NPC and transport during apoptosis have not been characterized. We demonstrate that 5-FU, but not topotecan, increases NPC permeability, and disrupts Ran-mediated nuclear transport before the disruption of the NPC. This increased permeability is dependent on increased cellular calcium, as the Ca chelator BAPTA-AM, abolishes the effect. Furthermore, increased calcium alone was sufficient to disrupt the Ran gradient. Combination treatments of 5-FU with topotecan or irinotecan, similarly disrupted nuclear transport before disassembly of the NPC. In both single and combination treatments nuclear transport was disrupted before caspase 9 activation, indicating that 5-FU induces an early caspase-independent increase in NPC permeability and alteration of nuclear transport. Because Crm1-mediated nuclear export of tumor suppressors is linked to drug resistance we also examined the effect of 5-FU on the nuclear export of a specific target, topoisomerase. 5-FU treatment led to accumulation of topoisomerase in the nucleus and recovered the loss nuclear topoisomerase induced by irinotecan or topotecan, a known cause of drug resistance. Furthermore, 5-FU retains its ability to cause nuclear accumulation of p53 in the presence of irinotecan or topotecan. Our results reveal a new mechanism of action for these therapeutics during apoptosis, opening the door to other potential combination chemotherapies that employ 5-FU as a calcium mediated inhibitor of Crm1-induced nuclear export of tumor suppressors.

3,3’-Diindolylmethane induces apoptosis and autophagy in fission yeast

“…However, in our experiments, nuclear condensation and NE disruption happened much earlier than previous observations [28,29,63]. The disruption of nuclear transport and disassembly of the nuclear pore complex (NPC) occurs before caspase-9 activation in humans [64]. Therefore, it could be possible that the nuclear condensation and NE disruption by DIM in fission yeast, in the first 10 minutes of incubation, happen before apoptosis is induced.…”

3,3’-Diindolylmethane induces apoptosis and autophagy in fission yeast

“…However, in our experiments, nuclear condensation and NE disruption happened much earlier than previous observations [28,29,62]. The disruption of nuclear transport and disassembly of the nuclear pore complex (NPC) occurs before caspase-9 activation in humans [63]. Therefore, it could be possible that the nuclear condensation and NE disruption by DIM in fission yeast, in the first 10 minutes of incubation, happen before apoptosis is induced.…”

Alterations in the nucleocytoplasmic transport in apoptosis: Caspases lead the way

“…Moreover, caspase‐9 mediates a breakdown of the hydrophobicity‐based barrier inside NPC channel, increasing NE leakiness . On the other hand, in another study, the disruption of Ran‐mediated nuclear transport after 5‐flurouracil treatment was shown to precede caspase‐9 activation, indicating the caspase‐independent increase in NPC permeability . Consequently, the role of caspases in early apoptosis‐mediated alterations of nucleocytoplasmic transport remains controversial and demands further investigation.…”