Amiram Ravid | Tel Aviv University (original) (raw)

Papers by Amiram Ravid

The anticancer activity of the hormonal form of vitamin D, 1,25- dihydroxyvitamin D (1,25(OH)2D),... more The anticancer activity of the hormonal form of vitamin D, 1,25- dihydroxyvitamin D (1,25(OH)2D), is associated with inhibition of cell cycle progression, induction of differentiation, and apoptosis. In addition, 1,25(OH)2D3 augments the activity of anticancer agents that induce ex- cessive reactive oxygen species generation in their target cells. This study aimed to find out whether 1,25(OH)2D3, acting as a single

The Journal of steroid biochemistry and molecular biology, 2006

The anti-cancer activity of calcitriol, the active metabolite of Vitamin D, in the colon is usual... more The anti-cancer activity of calcitriol, the active metabolite of Vitamin D, in the colon is usually attributed to its anti-proliferative and pro-differentiative actions. The levels of reactive oxygen species (ROS) are high in colon carcinomas due to increased aerobic metabolism and exposure to various anti-cancer modalities. We examined whether calcitriol modulates the response of colon cancer cells to the cytotoxic action of the common mediator of ROS injury, H2O2. Pretreatment with calcitriol (100 nM, 48 h) sensitized HT-29 colon cancer cells to cell death induced by acute exposure to H2O2 or chronic exposure to the H2O2 generating system, glucose/glucose-oxidase. Although the morphological features of H2O2-induced HT-29 cell death are consistent with apoptosis, we detected no executioner caspase activation in response to cytotoxic concentrations of H2O2 and treatment with a pan-caspase inhibitor did not affect H2O2-induced cytotoxicity nor its enhancement by calcitriol. Conversel...

International journal of immunopharmacology, 1993

1,25-dihydroxyvitamin D3, the active metabolite of vitamin D, partially inhibits antigen and mito... more 1,25-dihydroxyvitamin D3, the active metabolite of vitamin D, partially inhibits antigen and mitogen-driven lymphocyte stimulation. We studied the effect of granulomatous inflammation on the sensitivity of lymphocytes to 1,25-dihydroxyvitamin D3 in vitro, measuring the inhibitory effect of 1,25-dihydroxyvitamin D3 on mitogenesis of splenocytes of mice with chronic inflammation induced by subcutaneous injection of talc. Systemic manifestations of the local inflammation included loss in body weight, splenomegaly, enhanced DNA synthesis by freshly isolated splenocytes and enhanced prostaglandin secretion by activated splenocytes. Splenocytes from animals with local inflammation were more susceptible to inhibition by 1,25-dihydroxyvitamin D3, but not by prostaglandin E2. This increased sensitivity to 1,25-dihydroxyvitamin D3 was abolished by blocking prostaglandin synthesis in splenocyte cultures with indomethacin and was restored by adding prostaglandin E2. This effect cannot be attrib...

Immunopharmacology, 1989

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) inhibits mitogen-induced lymphocyte proliferation in perip... more 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) inhibits mitogen-induced lymphocyte proliferation in peripheral blood mononuclear cell preparations. Receptors for 1,25(OH)2D3 are present in monocytes and are acquired by lymphocytes upon activation. It is not clear whether the hormone inhibits lymphocyte mitogenesis by a direct action on the lymphocyte or only indirectly by affecting the regulatory monocytes. We addressed this question by using highly purified human lymphocyte preparations which contain less than 0.1% monocytes. 1,25(OH)2D3 inhibited the stimulation of purified lymphocytes by phytohemagglutinin and in the presence of fixed accessory cells, which cannot respond to 1,25(OH)2D3. The inhibitory effect attained 35% similar to that obtained in the presence of monocytes. 1,25(OH)2D3 inhibited interleukin 2 (IL-2)-driven stimulation of purified T cells in three different systems: cells treated with a submitogenic concentration of phytohemagglutinin, IL-2-dependent cells which bear receptors for IL-2 and naive cells in the absence of other mitogens. We conclude: (1) the human T lymphocyte is a direct target for 1,25(OH)2D3; (2) 1,25(OH)2D3 inhibits the response of activated, IL-2-receptor-bearing human T cells to interleukin-2.

Transplantation, 2009

Mitochondrial calcium overload triggers apoptosis and also regulates ATP production. ATP and urid... more Mitochondrial calcium overload triggers apoptosis and also regulates ATP production. ATP and uridine-5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-triphosphate (UTP) depletion from hepatic tissue after ischemia causes cell death. ATP and UTP binds to cell membranes of the hepatocytes through P2Y receptors. Our aim was to investigate the role of UTP on the hepatic injury induced by ischemia. Isolated mouse livers were randomly divided into five groups: (1) control group; (2) ischemic group (90 min); (3) as group 2, but with the administration of UTP; (4) as group 2, but with the administration of suramin, a P2Y antagonist; and (5) as group 3, but with the simultaneous administration of suramin and UTP. There was a postischemic significant reduction in the release of liver enzymes in the animals pretreated with UTP, the intrahepatic caspase-3 activity was significantly decreased, and the intrahepatic ATP content increased compared with group 2 (ischemic untreated). UTP prevented intracellular Ca overload after hypoxia in hepatocyte cultures. In the UTP-treated groups, significantly fewer apoptotic hepatocyte cells were noted by weaker activation of caspase-3 and by the transferase-mediated dUTP nick end labeling assay. The administration of suramin prevented the beneficial effect of endogenous ATP. UTP treatment attenuated the degradation of IkappaBalpha (nuclear factor-kappaB inhibitor) by 80% during reperfusion with no effect on c-Jun N terminal kinase phosphorylation. The administration of UTP before induction of ischemia-reperfusion can attenuate hepatic injury. UTP administration decreased cytosolic Ca overload in hypoxic conditions. UTP-mediated protective effects may be regulated through nuclear factor- kappaB inactivation. These findings have important implications for the potential use of UTP in ischemic hepatic injury.

The Journal of Steroid Biochemistry and Molecular Biology, 2000

It was previously shown that 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ) enhances the cytotoxic a... more It was previously shown that 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ) enhances the cytotoxic activity of tumor necrosis factor a (TNFa), doxorubicin and menadione. A feature shared by these anticancer agents is the involvement of reactive oxygen species (ROS) in their action. In this work we found that 1,25(OH) 2 D 3 acted synergistically with interleukin 1 b (IL-1b) or interleukin 6 (IL-6) to inhibit the proliferation of MCF-7 breast cancer cells. The extent of the synergism was maximal at 1 nM, a concentration at which 1,25(OH) 2 D 3 , acting singly, only marginally reduced the cell number. The thiol antioxidant, Nacetylcysteine (NAC) abolished the synergism between IL-1b or IL-6 and 1,25(OH) 2 D 3 , but had only a small protective eect when the cytokines acted alone. NAC and reduced glutathione (GSH) protected MCF-7 cells from cytotoxicity induced both by TNFa alone and by TNFa and 1,25(OH) 2 D 3 . A two-day exposure to TNFa caused a 27X723X17 (mean 2 SEM) reduction in GSH content. This eect increased to 46X425X57 by co-treatment with 1,25(OH) 2 D 3 which did not aect GSH levels on it own. We conclude that 1,25(OH) 2 D 3 can act synergistically with anticancer cytokines present in the tumor milieu and that ROS plays a mediatory role in this interaction. 7

The Journal of Steroid Biochemistry and Molecular Biology, 2004

Calcitriol, the hormonal form of Vitamin D, potentiates the activity of some agents of the anti-c... more Calcitriol, the hormonal form of Vitamin D, potentiates the activity of some agents of the anti-cancer immune system including tumor necrosis factor-␣ (TNF-␣). Different signaling pathways activated by TNF-␣ may be targets for calcitriol action. Activation of p38 MAP kinase was shown to have both pro-and anti-apoptotic actions in TNF-␣-induced programmed cell death depending on cell context. Treatment of MCF-7 breast cancer cells with TNF-␣ resulted in activation of p38 MAP kinase that persisted for at least 24 h. Whereas calcitriol had no effect on the earlier phase of p38 MAP kinase activation (up to 1 h), it inhibited the activation of this pathway between one and 24 h after exposure to TNF-␣. Both calcitriol and the p38 MAP kinase inhibitor SB203580 enhanced TNF-␣-induced cytotoxicity and drop in mitochondrial membrane potential, but their combined effect was sub-additive. Taken together, these findings suggest that p38 MAP kinase plays an anti-apoptotic role in TNF-␣-induced cytotoxicity in MCF-7 cells and that the synergistic interaction between TNF-␣ and calcitriol, leading to mitochondrial damage and subsequent cell death, is partially due to modulation of this signaling pathway.

Proceedings of the National Academy of Sciences, 1982

Agents that are known to be scavengers of hydroxyl radicals inhibit lymphocyte mitogenesis induce... more Agents that are known to be scavengers of hydroxyl radicals inhibit lymphocyte mitogenesis induced by phorbol myristate acetate (PMA) to a greater extent than they inhibit mitogenesis induced by concanavalin A or phytohemagglutinin. These agents include dimethyl sulfoxide, benzoate, thiourea, dimethylurea, tetramethylurea, L-tryptophan, mannitol, and several other alcohols. Their inhibitory effect is not associated with cytotoxicity. The hydroxyl radical scavengers do not inhibit PMA-dependent amino acid transport in T cells or PMA-induced superoxide production by monocytes. Thus, they do not inhibit the primary interaction of PMA with responding cells. Treatment of peripheral blood mononuclear cells with PMA increased cellular guanylate cyclase in most experiments, and dimethyl sulfoxide tended to inhibit this increase. In addition to inhibition of PMA-induced mitogenesis, hydroxyl radical scavengers markedly inhibited the activity of lymphocyte activating factor (interleukin 1). The differential inhibition of lymphocyte mitogenesis induced by different mitogens appears to be related to the differential macrophage requirements of the mitogens. The data suggest that hydroxyl radicals may be involved in mediating the triggering signal for lymphocyte activation. Some of the hydroxyl radical scavengers are inducers of cellular differentiation,. nd it is possible that their differentiating activity is related to their ability to scavenge free radicals.

Molecular and Cellular Endocrinology, 1992

Molecular and Cellular Endocrinology, 1993

The effect of 1,25-dihydroxyvitamin D3 on lymphokine-activated killer (LAK) cells activity was st... more The effect of 1,25-dihydroxyvitamin D3 on lymphokine-activated killer (LAK) cells activity was studied. Treatment of LAK cells with 1,25-dihydroxyvitamin D3 for 24 h increased their cytotoxic activity without affecting cell proliferation. This effect was dose-dependent, detectable already at 10(-11) M attaining 44 +/- 7% increase at 10(-8) M. 1,25-dihydroxyvitamin D3 increased LAK cell content of the cytotoxic granule granzyme A by 21%. Secretion of granzyme A by LAK cells was triggered by 12-O-tetradecanoylphorbol 13-acetate and the calcium ionophore A23187. 1,25-dihydroxyvitamin D3 decreased the lag preceding secretion, increased the rate constant of exocytosis and the fraction of granzyme A cell content secreted. The potentiation of exocytosis was more pronounced at suboptimal calcium ionophore concentration suggesting that 1,25-dihydroxyvitamin D3 affects a calcium-dependent process. Since exocytosis of cytotoxic granules is a pivotal event in the killing of tumor cells by LAK cells, it is plausible that the enhancement of this process underlies the stimulation of LAK cell cytotoxic activity by 1,25-dihydroxyvitamin D3.

Liver Transplantation, 2000

Journal of Endocrinology, 1996

Renal cell carcinoma is a chemotherapy-resistant tumor which is relatively responsive to immunoth... more Renal cell carcinoma is a chemotherapy-resistant tumor which is relatively responsive to immunotherapy. Immunotherapeutic regimes employ interferons or interleukin 2 with or without lymphokine-activated killer cells. Secondary cytokines, induced by interleukin 2 or interferon, may have an important impact on their anti-neoplastic activity. Notable among them is tumor necrosis factor (TNF alpha). We assessed the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on the susceptibility of the human renal cell carcinoma cell line SK-RC-29 to the cytotoxic and cytostatic actions of TNF alpha, interferon alpha and lymphokine-activated killer cells. Using uptake of the vital dye neutral red as an indicator of viable cell number, we found that addition of 1,25(OH)2D3 (100 nM) to TNF alpha (30 ng/ml)-treated cultures resulted in a 2.6 +/- 0.2-fold (mean +/- S.E.) increase in the cytotoxic effect of the cytokine. The potentiating effect of 1,25(OH)2D3 was dose-dependent, and significant at concentrations equal to or higher than 10 nM. Another dihydroxylated vitamin D metabolite, 24,25(OH)2D3, had no effect on TNF alpha action. The cytotoxic effect of TNF alpha increased whereas the potentiation by 1,25(OH)2D3 decreased with cell density in culture. 1,25(OH)2D3, in contrast to its potentiating effect on TNF alpha action, did not modulate the cytostatic effect of interferon alpha or the susceptibility of SK-RC-29 to killing by lymphokine-activated killer cells. The findings reported here may explain some of the in vivo anti-tumor activity of 1,25(OH)2D3 and provide a rationale for the employment of active vitamin D analogs during immune anti-cancer therapy.

Journal of Endocrinology, 2002

In addition to its known effects on keratinocyte proliferation and differentiation, the hormonal ... more In addition to its known effects on keratinocyte proliferation and differentiation, the hormonal form of vitamin D, 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), has been shown to protect keratinocytes from UV-and chemotherapy-induced damage. Epidermal keratinocytes contain both the machinery needed to produce 1,25(OH) 2 D 3 and vitamin D receptors. The activation of the stress-activated protein kinases (SAPKs), such as c-Jun N-terminal kinase (JNK) and p38, is an early cellular response to stress signals and an important determinant of cell fate. This study examines whether modulation of these SAPKs is associated with the effects of 1,25(OH) 2 D 3 on keratinocytes under stress. HaCaT keratinocytes were exposed to heat shock, hyperosmotic concentrations of sorbitol, the epidermal growth factor receptor tyrosine kinase inhibitor AG1487, the pro-inflammatory cytokine tumor necrosis factor , and H 2 O 2 . These stresses activated both SAPKs. Pretreatment with 1,25(OH) 2 D 3 inhibited the activation of JNK by all stresses and the activation of p38 by heat shock, AG1478 and tumor necrosis factor . Under the same conditions, treatment with 1,25(OH) 2 D 3 protected HaCaT keratinocytes from cytotoxicity induced by exposure to H 2 O 2 and hyperosmotic shock. The effect of 1,25(OH) 2 D 3 was dosedependent, already apparent at nanomolar concentrations, and time-dependent, maximal after a 24-h pre-incubation. We suggest that inhibition of SAPK activation may account for some of the well-documented protective effects of 1,25(OH) 2 D 3 on epidermal cells during exposure to UV or chemotherapy and may also be related to the anti-inflammatory actions of the hormone in skin.

Journal of Clinical Investigation, 1985

Lectin-induced DNA synthesis by peripheral mononuclear cells from 17 normal donors was inhibited ... more Lectin-induced DNA synthesis by peripheral mononuclear cells from 17 normal donors was inhibited (40-60%) by 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) at physiological concentrations (10(-10)-10(-9) M). The lymphocytes acquire specific receptors for 1,25(OH)2D3 upon activation by the lectins. This process precedes the inhibitory effect of 1,25(OH)2D3. We studied lymphocytes from six patients from four different kindreds with the syndrome of hereditary end-organ resistance to 1,25(OH)2D (the so-called vitamin D-dependent rickets type II). In five patients (three kindreds) peripheral blood mononuclear cells did not acquire receptors for 1,25(OH)2D3 upon phytohemagglutinin-induced activation. Moreover, in contrast to normal lymphocytes, the mitogenic stimulation of these patients' lymphocytes by phytohemagglutinin and concanavalin A was not inhibited by 1,25(OH)2D3. Activated lymphocytes of the sixth patient from a fourth kindred exhibited normal binding of [3H]1,25(OH)2D3 but the hormone failed to inhibit the mitogenic stimulation. A similar pattern of the vitamin D effector system was previously observed in fibroblasts cultured from skin biopsies of the same group of patients. The conclusions from these findings are: (a) the inhibition of mitogenic stimulation by 1,25(OH)2D3 is mediated by specific functional receptors to the hormone; and (b) the receptors for 1,25(OH)2D3 in mononuclear cells are probably controlled genetically by the same mechanisms as the effector system in well-characterized target organs of the hormone, such as intestine and kidney.

The Journal of Clinical Endocrinology & Metabolism, 1990

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3], like the immune response modulators prostaglandin E2 (PG... more 1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3], like the immune response modulators prostaglandin E2 (PGE2) and histamine, inhibits mitogen-induced proliferation of human peripheral blood mononuclear cells. 1,25-(OH)2D3 acts synergistically with PGE2 and histamine to inhibit lymphocyte mitogenesis. This is apparent at a wide concentration range of 1,25-(OH)2D3 (3 X 10(-11)-10(-8) mol/L). Cholera toxin, forskolin, and isobutylmethylxanthine, which like PGE2 and histamine increase intracellular concentrations of cAMP, also act synergistically with 1,25-(OH)2D3 in this system. Culture of mitogen-stimulated adherent cell-depleted mononuclear cells with PGE2 increases the number of high affinity binding sites for 1,25-(OH)2D3. This finding may account for the synergistic interaction between the two agents.

The Journal of Clinical Endocrinology & Metabolism, 1988

1,25-Dihydroxyvitamin D [1,25-(OH) 2 D] inhibits mitogen-induced proliferation of lymphocytes by ... more 1,25-Dihydroxyvitamin D [1,25-(OH) 2 D] inhibits mitogen-induced proliferation of lymphocytes by a receptormediated mechanism. Peripheral blood lymphocytes may serve as a model for detecting hereditary defects in the response of classical target organs to 1,25-(OH) 2 D. ...

Journal of Cellular Physiology, 2000

MMP-9, a member of the matrix metalloproteinase family that degrades collagen IV and processes ch... more MMP-9, a member of the matrix metalloproteinase family that degrades collagen IV and processes chemokines and cytokines, participates in epidermal remodeling in response to stress and injury. Limited activity of MMP-9 is essential while excessive activity is deleterious to the healing process. Tumor necrosis factor (TNFa), a key mediator of cutaneous inflammation, is a powerful inducer of MMP-9. Calcitriol, the hormonally active vitamin D metabolite, and its analogs are known to attenuate epidermal inflammation. We aimed to examine the modulation of MMP-9 by calcitriol in TNFa-treated keratinocytes. The immortalized HaCaT keratinocytes were treated with TNFa in the absence of exogenous growth factors or active ingredients. MMP-9 production was quantified by gelatin zymography and real-time RT-PCR. Activation of signaling cascades was assessed by western blot analysis and DNA-binding activity of transcription factors was determined by EMSA. Exposure to TNFa markedly increased the protein and mRNA levels of MMP-9, while pretreatment with calcitriol dose dependently reduced this effect. Employing specific inhibitors we established that the induction of MMP-9 by TNFa was dependent on the activity of the epidermal growth factor receptor, c-Jun-N-terminal kinase (JNK), NFkB and extracellular signal-regulated kinase-1/ 2. The effect of calcitriol was associated with inhibition of JNK activation and reduction of DNA-binding activities of the transcription factors activator protein-1 (AP-1) and NFkB following treatment with TNFa. By down-regulating MMP-9 levels active vitamin D derivatives may attenuate deleterious effects due to excessive TNFa-induced proteolytic activity associated with cutaneous inflammation.

Journal of Cellular Physiology, 2012

The hormonal form of vitamin D, calcitriol, and its analogs are known for their beneficial effect... more The hormonal form of vitamin D, calcitriol, and its analogs are known for their beneficial effect in the treatment of inflammatory skin disorders. Keratinocytes play a role in epidermal inflammatory responses invoked by breeching of the epidermal barrier, by infectious agents and by infiltrating immune cells. We studied the role of calcitriol in the initiation of keratinocyte inflammatory response by the viral and injury mimic polyinosinic-polycytidylic acid (poly(I:C)) and in its maintenance by tumor-necrosis-factor α (TNFα) and investigated the role of the mitogen-activated protein kinase cascades in these processes and their regulation by calcitriol. The inflammatory response of human HaCaT keratinocytes to poly(I:C) or TNFα was assessed by measuring mRNA levels of 13 inflammation-related molecules by real-time PCR microarray and by in-depth investigation of the regulation of interleukin 8, intercellular-adhesion-molecule 1, and TNFα expression. We found that while calcitriol had only a minor effect on the keratinocyte response to poly(I:C) and a modest effect on the early response (2 h) to TNFα, it markedly attenuated the later response (16-24 h) to TNFα. The expression of CYP27B1, the enzyme responsible for calcitriol production, was marginally increased by poly(I:C) and markedly by TNFα treatment. This pattern suggests that while allowing the initial keratinocyte inflammatory response to proceed, calcitriol contributes to its timely resolution. Using pharmacological inhibitors we found that while the p38 MAPK and the extracellular signal-regulated kinase have only a minor role, c-Jun N-terminal kinase plays a pivotal role in the induction of the pro-inflammatory genes and its modulation by calcitriol.

Journal of Cellular Biochemistry, 2008

Inflammation, elicited in the skin following tissue damage or pathogen invasion, may become chron... more 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.

Journal of Cellular Biochemistry, 2003

The hormonally active vitamin D metabolite, 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), and kera... more The hormonally active vitamin D metabolite, 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), and keratinocyte growth factor (KGF) belong to the network of autocrine and paracrine mediators in the skin. Both were shown to modulate keratinocyte proliferation, to reverse epidermal atrophy, to increase wound healing, and to reduce chemotherapy-induced alopecia. The overlap between their activities may suggest that vitamin D exerts some of its actions by modulation of KGF activities in the skin. This notion was examined by using HaCaT keratinocytes cultured in serum-free medium in the absence of exogenous growth factors and in the presence of the EGF receptor tyrosine kinase inhibitor AG 1478 that blocks their autonomous proliferation. These cells could be stimulated to proliferate by different fibroblast growth factors (FGFs). The relative mitogenic efficacy of basic FGF, acidic FGF, or KGF was in correlation with their affinities for the KGF receptor (KGFR). Forty-eight hour co-treatment with 1,25(OH) 2 D 3 enhanced KGFR-mediated cell proliferation in a dose dependent manner. Both ERK1/2 and c-Jun N-terminal kinase (JNK) were activated by the FGFs. Treatment with 1,25(OH) 2 D 3 increased the activation of ERK but reduced the activation of JNK. Treatment with 1,25(OH) 2 D 3 increased the levels of KGFR in the presence but not in the absence of KGF, probably due to inhibition of ligand-induced receptor degradation. Inhibition of protein kinase C with bisindolylmaleimide did not interfere with the effect of 1,25(OH) 2 D 3 on KGFR-mediated ERK activation. Our results support the notion that the paracrine KGF-KGFR system in the skin can act in concert with the autocrine vitamin D system in keratinocytes to promote keratinocyte proliferation and survival under situations of stress and injury.