Regulation of Ca2+ influx during mitosis: Ca2+ influx and depletion of intracellular Ca2+ stores are coupled in interphase but not mitosis.

Abstract

Activation of a wide variety of membrane receptors leads to a sustained elevation of intracellular Ca2+ ([Ca2+]i) that is pivotal to subsequent cell responses. In general, in nonexcitable cells this elevation of [Ca2+]i results from two sources: an initial release of Ca2+ from intracellular stores followed by an influx of extracellular Ca2+. These two phases, release from intracellular stores and Ca2+ influx, are generally coupled: stimulation of influx is coordinated with depletion of Ca2+ from stores, although the mechanism of coupling is unclear. We have previously shown that histamine effects a typical [Ca2+]i response in interphase HeLa cells: a rapid rise in [Ca2+]i followed by a sustained elevation, the latter dependent entirely on extracellular Ca2+. In mitotic cells only the initial elevation, derived by Ca2+ release from intracellular stores, occurs. Thus, in mitotic cells the coupling of stores to influx may be specifically broken. In this report we first provide additional evidence that histamine-stimulated Ca2+ influx is strongly inhibited in mitotic cells. We show that efflux is also strongly stimulated by histamine in interphase cells but not in mitotics. It is possible, thus, that in mitotics intracellular stores are only very briefly depleted of Ca2+, being replenished by reuptake of Ca2+ that is retained within the cell. To ensure the depletion of Ca2+ stores in mitotic cells, we employed the sesquiterpenelactone, thapsigargin, that is known to affect the selective release of Ca2+ from intracellular stores by inhibition of a specific Ca(2+)-ATPase; reuptake is inhibited. In most cells, and in accord with Putney's capacitative model (1990), thapsigargin, presumably by depleting intracellular Ca2+ stores, stimulates Ca2+ influx. This is the case for interphase HeLa cells. Thapsigargin induces an increase in [Ca2+]i that is dependent on extracellular Ca2+ and is associated with a strong stimulation of 45Ca2+ influx. In mitotic cells thapsigargin also induces a [Ca2+]i elevation that is initially comparable in magnitude and largely independent of extracellular Ca2+. However, unlike interphase cells, in mitotic cells the elevation of [Ca2+]i is not sustained and 45Ca2+ influx is not stimulated by thapsigargin. Thus, the coupling between depletion of intracellular stores and Ca2+ influx is specifically broken in mitotic cells. Uncoupling could account for the failure of histamine to stimulate Ca2+ influx during mitosis and would effectively block all stimuli whose effects are mediated by Ca2+ influx and sustained elevations of [Ca2+]i.

Orai1 internalization and STIM1 clustering inhibition modulate SOCE inactivation during meiosis

“…SOCE is inhibited as the oocyte commits to meiosis (12), and MPF activation is sufficient for SOCE inactivation (12). As is the case in Xenopus eggs, SOCE inactivates during mitosis of mammalian cells (13,18). Here we show that SOCE inactivation during meiosis is the result of Orai1 internalization and to the inability of STIM1 to cluster in response to store depletion.…”

“…Inactivation of Ca 2ϩ influx during M phase of the cell cycle has been described during both mitosis of mammalian cells (13) and Xenopus oocyte meiosis (11), and hence appears to be a conserved mechanism during cell division. The exception is mammalian eggs, which undergo prolonged Ca 2ϩ oscillations postfertilization and maintain an active SOCE (30).…”

“…Although physiologically SOCE is coupled to Ca 2ϩ release from stores in response to G protein or tyrosine kinase coupled receptors, Ca 2ϩ release per se is not required, rather it is coupling between luminal ER Ca 2ϩ levels and Orai1 through STIM1 that regulates SOCE. The only known physiological case where this coupling is disrupted is during M phase of the cell cycle (11)(12)(13).…”

Ca2+ signaling differentiation during oocyte maturation

“…Furthermore, as is the case in Xenopus eggs, SOCE inactivates during mitosis of mammalian cells (Preston et al, 1991;Tani et al, 2007), arguing that MPF activation typically leads to SOCE inactivation, since mitosis also requires MPF/cdk1. Therefore, mammalian eggs are the exception in terms of maintaining SOCE functional during the division phase of the cell cycle.…”

Microtubule remodeling mediates the inhibition of store-operated calcium entry (SOCE) during mitosis in COS-7 cells

“…We recently observed that, unlike interphase cells, the depletion of intracellular calcium stores with ATP was not followed by SOCE in mitotic cells which indicates the inhibition of this vital [Ca 2+ ]i -regulating mechanism. A few reports have implied either a down-regulation or a complete absence of SOCE in mitotic cells presumably due to uncoupling between cell surface channels and the ER (Volpi and Berlin, 1988;Preston et al, 1991;Tani et al, 2007). However, no attempts have been made to substantiate these findings and possibly shed some light on the cellular mechanisms involved.…”