Carmela Rotem

1,25-Dihydroxyvitamin D3 enhances degranulation of mast cells.

The mast cell lines rat basophilic leukemia (RBL) and mouse C57 cells respond to IgE/antigen complexes by degranulation. Treatment of these cells with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), (10-100 nM) for 24-48 h enhanced IgE/antigen-induced exocytosis as monitored by release of hexosaminidase. A short term incubation with the hormone did not affect exocytosis, ruling out a rapid non genomic mechanism. The presence of vitamin D receptors, demonstrated by immunoblotting and the lack of effect of 24,25(OH)2D3 suggest a role for these receptors in the enhancing effect. 1,25(OH)2D3 also enhanced exocytosis induced by the calcium ionophore A23187 in the presence or absence of phorbol ester indicating modulation of events distal to signal transduction. 1,25(OH)2D3 enhanced exocytosis in the presence of cytochalasin D, indicating that the action of the hormone is not due to effects on microfilament structure. The results of this study suggest that 1,25(OH)2D3 may affect the allergic or pro-inflammatory potential of mast cells.

Two modes of ERK activation by TNF in keratinocytes: Different cellular outcomes and bi‐directional modulation by vitamin D

Inflammation, elicited in the skin following tissue damage or pathogen invasion, may become chronic with deleterious consequences. Tumor necrosis factor (TNF) is a key mediator of cutaneous inflammation and the keratinocyte an important protagonist of skin immunity. Calcitriol, the hormonally active vitamin D metabolite, and its analogs attenuate epidermal inflammation and inhibit the hyperproliferation of keratinocytes associated with the inflammatory disorder, psoriasis. Since activation of extracellular signal‐regulated kinase (ERK) promotes keratinocyte proliferation and mediates epidermal inflammation, we studied the effect of calcitriol on ERK activation in HaCaT keratinocytes exposed to the ubiquitous inflammatory cytokine TNF. By using the EGF receptor (EGFR) tyrosine kinase inhibitor, AG1487 and the Src family inhibitor, PP‐1, we established that TNF activated ERK in an EGFR and Src dependent and an EGFR and Src independent modes. EGFR dependent activation resulted in the upregulation of the transcription factor, c‐Fos, while the EGFR independent activation mode was of a shorter duration, did not affect c‐Fos expression but induced IL‐8 mRNA expression. Pretreatment with calcitriol, enhanced TNF‐induced EGFR‐Src dependent ERK activation and tyrosine phosphorylation of the EGFR, but abolished the EGFR‐Src independent ERK activation. These effects were mirrored by enhancement of c‐Fos and inhibition of IL‐8 induction by TNF. Treatment with calcitriol increased the rate of the de‐phosphorylation of activated ERK, accounting for the inhibition of EGFR‐Src independent ERK activation by TNF. It is possible that effects on the ERK cascade contribute to the effects of calcitriol and its synthetic analogs on cutaneous inflammation and keratinocyte proliferation. J. Cell. Biochem. 104: 606–619, 2008.

1,25-dihydroxyvitamin D3 potentiates the decreased response of lymphocytes from atopic subjects to agents that increase intracellular cyclic adenosine monophosphate

The inhibitory effect of prostaglandin E2, histamine, isobutylmethylxanthine, and 1,25-dihydroxyvitamin D3 (1,25-[OH]2D3) on the mitogenic stimulation of peripheral blood lymphocytes from normal and atopic subjects was studied. We found that lymphocytes from atopic patients were less susceptible to inhibition by the three agents that elevate intracellular cyclic adenosine monophosphate (cAMP) concentrations and by the active metabolite of vitamin D (inhibition of 27%, 14%, 12%, and 36% for the atopic patients as compared with 40%, 20%, 22%, and 46% for the normal donors, by the four agents, respectively; p less than 0.02). The inhibitory effect of the cAMP-elevating agents was potentiated by the addition of 1,25-(OH)2D3 to the lymphocyte cultures. The potentiation was more pronounced on lymphocytes from the atopic donors, increasing their responsiveness to levels comparable to levels of lymphocytes from normal donors. The synthetic corticosteroid, dexamethasone, had a similar potentiating effect on the inhibitory action of prostaglandin E2. In view of the beneficial action of beta-agonists, phosphodiesterase inhibitors, and corticosteroids in the treatment of allergy, the potentiating effect of 1,25-(OH)2D3 on the action of cAMP-elevating agents may be of therapeutic interest.

Vitamin D Induces Cyclooxygenase 2 Dependent Prostaglandin E2 Synthesis in HaCaT Keratinocytes

The active metabolite of vitamin D calcitriol and its analogs are well‐known for their anti‐inflammatory action in the skin, while their main side effect associated with topical treatment of inflammatory disorders is irritant contact dermatitis. Prostaglandin E2 (PGE2) is pro‐inflammatory at the onset of inflammation and anti‐inflammatory at its resolution. We hypothesized that induction of PGE2 synthesis by calcitriol in epidermal keratinocytes may contribute both to its pro‐inflammatory and anti‐inflammatory effects on the skin. Treatment of human immortalized HaCaT keratinocytes with calcitriol (3–100 nM, 2–24 h) increased PGE2 production due to increased mRNA and protein expression of COX‐2, but not to increase of COX‐1 or release of arachidonic acid. The effect of calcitriol on COX‐2 mRNA was observed also in primary human keratinocytes. The increase in COX‐2 mRNA is associated with COX‐2 transcript stabilization. Calcitriol exerts this effect by a rapid (2 h) and protein synthesis independent mode of action that is dependent on PKC and Src kinase activities. Treatment with a COX‐2 inhibitor partially prevented the attenuation of the keratinocyte inflammatory response by calcitriol. We conclude that upregulation of COX‐2 expression with the consequent increase in PGE2 synthesis may be one of the mechanisms explaining the Janus face of calcitriol as both a promoter and attenuator of cutaneous inflammation. J. Cell. Physiol. 231: 837–843, 2016.