Up-regulation of Ca2+ influx mediated by store-operated channels in HL60 cells induced to differentiate by 1α,25-Dihydroxyvitamin D3
✍ Scribed by Jeffrey P. Gardner; M. Balasubramanyam; George P. Studzinski
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 334 KB
- Volume
- 172
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
The physiologically active form of vitamin D, 1a,25-dihydroxyvitamin D 3 (1,25D 3 ), induces promyelocytic HL60 cells to differentiate towards monocytelike cells. During this differentiation increased cytosolic calcium (Ca 2/ i ) and expression of surface receptors for chemotactic factors ''prime'' the cell for the activation of monocyte functions and the triggering of the respiratory burst pathway. We examined whether the Ca 2/ influx mediated by store-operated channels (SOC) contributed to the increased Ca 2/ i following exposure of HL60 cells to 10 07 M 1,25D 3 . Cells treated with 1,25D 3 for 72 hr demonstrated a rapid transient rise in Ca 2/ i followed by a second, phasic, increase in Ca 2/ i in response to the purinergic agonist ATP. This second Ca 2/ i transient was blocked by Ni 2/ , SKF 96365, or withdrawal of extracellular Ca 2/ . In cells suspended in Ca 2/ -free medium, peak changes (D) in [Ca 2/ ] i elicited by ATP-induced Ca 2/ mobilization occurred with similar EC 50 values in differentiated and vehicle (EtOH)-treated cells; however, peak [Ca 2/ ] i was reduced by 55% in 1,25D 3 -treated cells. Decreased Ca 2/ mobilization was associated with a 25-35% reduction in intracellular Ca 2/ stores (determined with ionomycin). 1,25D 3 -treated cells exposed to ATP or thapsigargin (Tg) in Ca 2/ -free medium for 3 min with subsequent addition of 1 mM Ca 2/ exhibited a respective 80% or 120% stimulation in peak [Ca 2/ ] i compared to EtOH-treated cells. Enhanced Ca 2/ influx mediated by SOC was also seen in these cells as an increase in the rate of Mn 2/ entry after exposure to ATP or Tg. At 96 hr after addition of 1,25D 3 , when differentiated phenotype was established, basal Ca 2/ i and Ca 2/ entry mediated by SOC returned to control values, but Ca 2/ store size remained reduced. Up-regulation of Ca 2/ influx via the SOC pathway during 1,25D 3 -induced differentiation may contribute to the functional properties of the maturing monocyte, or to the resetting of molecular programs responsible for the changing phenotype.