Modulation of glioma BK channels via erbB2.
Glioma cells show up-regulation and constitutive activation of erbB2, and its expression correlates positively with increased malignancy. A similar correlation has been demonstrated for the expression of gBK, a calcium-sensitive, large-conductance K(+) channel. We show here that glioma BK channels are a downstream target of erbB2/neuregulin signaling. Tyrphostin AG825 was able to disrupt the constituitive erbB2 activation in a dose-dependent manner, causing a 30-mV positive shift in gBK channel activation in cell-attached patches. Conversely, maximal stimulation of erbB2 with a recombinant neuregulin (NRG-1beta) caused a 12-mV shift in the opposite direction. RT-PCR studies reveal no change in the BK splice variants expressed in treated glioma cells. Furthermore, isolation of surface proteins through biotinylation did not show a change in gBK channel expression, and probing with phospho-specific antibodies showed no alteration in channel phosphorylation. However, fura-II Ca(2+) fluorescence imaging revealed a 35% decrease in the free intracellular Ca(2+) concentration after erbB2 inhibition and an increase in NRG-1beta-treated cells, suggesting that the observed changes most likely were due to alterations in [Ca(2+)](i). Consistent with this conclusion, neither tyrphostin AG825 nor NRG-1beta was able to modulate gBK channels under inside-out or whole-cell recording conditions when intracellular Ca(2+) was fixed. Thus, gBK channels are a downstream target for the abundantly expressed neuregulin-1 receptor erbB2 in glioma cells. However, unlike the case in other systems, this modulation appears to occur via changes in [Ca(2+)](i) without changes in channel expression or phosphorylation. The enhanced sensitivity of gBK channels in glioma cells to small, physiological Ca(2+) changes appears to be a prerequisite for this modulation.
Olsen
M L
ML
Department of Neurobiology and Civitan International Research Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Weaver
A K
AK
Ritch
P S
PS
Sontheimer
H
H
D052160:Benzothiazoles; D001932:Brain Neoplasms / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D005909:Glioblastoma / Q000378:metabolism*; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels; D020880:Neuregulins / Q000378:metabolism; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D020032:Tyrphostins / Q000494:pharmacology
D052160:Benzothiazoles; D002118:Calcium; D051036:Large-Conductance Calcium-Activated Potassium Channels; D020880:Neuregulins; D024681:Potassium Channels, Calcium-Activated; D011505:Protein-Tyrosine Kinases; D018719:Erb-b2 Receptor Tyrosine Kinases; D020032:Tyrphostins; C098214:tyrphostin AG825