Commitment to differentiation of murine erythroleukemia cells involves a modulated plasma membrane depolarization through Ca²⁺‐activated K⁺ channels

Abstract

The role of the plasma membrane potential (delta psi p) in the commitment to differentiation of murine erythroleukemia (MEL) cells has been studied by analyzing the ionic basis and the time course of this potential in the absence or the presence of different types of inducers. delta psi p was determined by measuring the distribution of tetraphenylphosphonium (TPP+) across the plasma membrane and displayed a 22-hour depolarization phase (from -28 to +5 mV) triggered by factors contained in foetal calf serum (FCS) and followed by a nearly symmetrical repolarization phase. After measuring the electrochemical equilibrium potential of Na+, K+, and Cl-, the relative contribution of these ions to delta psi p was evaluated by means of ion substitution experiments and by the addition of ion flux inhibitors (tetrodotoxin [TTX], 4-acetoamide-4'-isothiocyanostilbene-2,2'-disulfonate [SITS]) and ionophores (Valinomycin, A23187). The Na+ contribution to delta psi p appeared negligible, the potential being essentially generated by K+ and Cl- fluxes. When evaluated by a new mathematical approach, the effects of Valinomycin and A23187 at different times of incubation provided evidence that both the depolarization and the repolarization phase were due to variations of the K+ permeability across the plasma membrane (PK) mediated by Ca2+-activated K+ channels. All the inducers tested (dimethylsulfoxide [DMSO], hexamethylen-bis-acetamide [HMBA], diazepam), although they did not modify the ionic basis of delta psi p, strongly attenuated the depolarization rate of this potential. This attenuation was not brought about when the inducers were added to noninducible MEL cell clonal sublines. Cell commitment occurred only during the depolarization phase and increased proportionally to the attenuation of this phase up to a threshold beyond which the further increase of the attenuation was associated with the inhibition of commitment. The major role of the inducers apparently consisted of the stabilization of the Ca2+-activated K+ channels, suggesting that a properly modulated delta psi p depolarization through these channels is primarily involved in the signal generation for MEL cell commitment to differentiation.

Polar/apolar compounds induce leukemia cell differentiation by modulating cell-surface potential.

“…These compounds contain an apolar region linked to one or more polar molecular groups, so that their essential feature is a combination of hydrophobicity and a high dipole moment (5,6), and their target is the plasma membrane (ref. 7 and references therein). Studies (7) based on the use of lipophilic cations indicated that the electrical potential across the plasma membrane was implicated in leukemia cell commitment to differentiation by DMSO and HMBA.…”

“…7 and references therein). Studies (7) based on the use of lipophilic cations indicated that the electrical potential across the plasma membrane was implicated in leukemia cell commitment to differentiation by DMSO and HMBA. To deepen this observation it was necessary to distinguish the contribution given to the true transmembrane potential (O.)…”

A transient dephosphorylation of JAK1 and JAK2 characterises the early-phase response of murine erythroleukemia cells to the differentiation inducer hexamethylenebisacetamide

“…23 A completely different response of JAKs was obtained when HMBA was added to the MELC clone selected for its resistance to the HMBA-inducing activity (12-H clone). 17,18 In fact, as shown in Figure 4, both JAK1 and JAK2 were constitutively expressed in 12-H cells, but as opposed to the wild-type cells, did not display any HMBA-inducible down-modulation of their tyrosine phosphorylation.…”

“…The MELC 12-H clone, selected in our laboratory for its insensitivity to the differentiating activity of HMBA and DMSO, 17,18 was routinely cultured in standard medium supplemented with 5 mM HMBA.…”

A porphobilinogen deaminase (PBGD) Ran-binding protein interaction is implicated in nuclear trafficking of PBGD in differentiating glioma cells

“…Recent studies implicate hyperacetylation and deacetylation as playing an important role in oncogenesis (Archer and Hodin, 1999). Unlike butyrate, HMBA is a potent inducer of differentiation belonging to the group of hybrid polar compounds (Rifkind et al, 1996), so that its essential feature is a combination of hydrophobicity and a high dipole moment (Breslow et al, 1991), and thus its cellular target is the plasma membrane (Arcangeli et al, 1987). HMBA acts by modulating the surface potential of the cell (Arcangeli et al, 1993), and some other findings suggest that a PKC-modulated signaling pathway may be involved in HMBA-induced murine erythroleukemia cell differentiation (Marks et al, 1994).…”