1,25-Dihydroxyvitamin D3 increases epidermal growth factor receptor gene expression in BT-20 breast carcinoma cells

Vitamin D and Its Potential Interplay With Pain Signaling Pathways

About 50 million of the U.S. adult population suffer from chronic pain. It is a complex disease in its own right for which currently available analgesics have been deemed woefully inadequate since ~20% of the sufferers derive no benefit. Vitamin D, known for its role in calcium homeostasis and bone metabolism, is thought to be of clinical benefit in treating chronic pain without the side-effects of currently available analgesics. A strong correlation between hypovitaminosis D and incidence of bone pain is known. However, the potential underlying mechanisms by which vitamin D might exert its analgesic effects are poorly understood. In this review, we discuss pathways involved in pain sensing and processing primarily at the level of dorsal root ganglion (DRG) neurons and the potential interplay between vitamin D, its receptor (VDR) and known specific pain signaling pathways including nerve growth factor (NGF), glial-derived neurotrophic factor (GDNF), epidermal growth factor receptor (EGFR), and opioid receptors. We also discuss how vitamin D/VDR might influence immune cells and pain sensitization as well as review the increasingly important topic of vitamin D toxicity. Further in vitro and in vivo experimental studies will be required to study these potential interactions specifically in pain models. Such studies could highlight the potential usefulness of vitamin D either alone or in combination with existing analgesics to better treat chronic pain.

Impact of Short-term 1,25-Dihydroxyvitamin D3 on the Chemopreventive Efficacy of Erlotinib against Oral Cancer

Activation of the epidermal growth factor receptor (EGFR) pathway is an early event in head and neck carcinogenesis. As a result, targeting EGFR for chemoprevention of head and neck squamous cell carcinomas (HNSCC) has received considerable attention. In the present study, we examined the impact of 1,25(OH)2D3, the active metabolite of the nutritional supplement vitamin D on the chemopreventive efficacy of the EGFR inhibitor, erlotinib, against HNSCC. Experimental studies were conducted in patient-derived xenografts (PDX) and the 4-nitroquinoline-1-oxide (4NQO) carcinogen-induced model of HNSCC. Short-term treatment (4 weeks) of PDX-bearing mice with 1,25(OH)2D3 and erlotinib resulted in significant inhibition of tumor growth. Noninvasive MRI enabled longitudinal monitoring of disease progression in the 4NQO model with 100% of control animals showing evidence of neoplastic lesions by 24 weeks. Among the experimental groups, animals treated with the combination regimen showed the greatest reduction in tumor incidence and volume (P < 0.05). Combination treatment was well tolerated and was not associated with any significant change in body weight. Histopathologic assessment revealed a significant reduction in the degree of dysplasia with combination treatment. Immunoblot analysis of whole tongue extracts showed downregulation of phospho-EGFR and phospho-Akt with the combination regimen. These results highlight the potential of 1,25(OH)2D3 to augment the efficacy of erlotinib against HNSCC. Further optimization of schedule and sequence of this combination regimen along with investigation into the activity of less calcemic analogues or dietary vitamin D is essential to fully realize the potential of this approach.

Interaction of vitamin D with membrane-based signaling pathways

Many studies in different biological systems have revealed that 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃) modulates signaling pathways triggered at the plasma membrane by agents such as Wnt, transforming growth factor (TGF)-β, epidermal growth factor (EGF), and others. In addition, 1α,25(OH)₂D₃ may affect gene expression by paracrine mechanisms that involve the regulation of cytokine or growth factor secretion by neighboring cells. Moreover, post-transcriptional and post-translational effects of 1α,25(OH)₂D₃ add to or overlap with its classical modulation of gene transcription rate. Together, these findings show that vitamin D receptor (VDR) cannot be considered only as a nuclear-acting, ligand-modulated transcription factor that binds to and controls the transcription of target genes. Instead, available data support the view that much of the complex biological activity of 1α,25(OH)₂D₃ resides in its capacity to interact with membrane-based signaling pathways and to modulate the expression and secretion of paracrine factors. Therefore, we propose that future research in the vitamin D field should focus on the interplay between 1α,25(OH)₂D₃ and agents that act at the plasma membrane, and on the analysis of intercellular communication. Global analyses such as RNA-Seq, transcriptomic arrays, and genome-wide ChIP are expected to dissect the interactions at the gene and molecular levels.

Vitamin D's role in cell proliferation and differentiation

Vitamin D has pleiotropic effects that go beyond its traditional role in calcium homeostasis. Hundreds of genes with vitamin D receptor response elements directly or indirectly influence cell cycling and proliferation, differentiation, and apoptosis. Vitamin D compounds also have effects on cell function that are nongenomic. The noncalcemic actions of vitamin D influence normal and pathological cell growth, carcinogenesis, immune function, and cardiovascular physiology. This review examines many of the various mechanisms by which vitamin D alters cellular growth and differentiation and explores cell-specific factors that influence responsiveness to vitamin D.

Growth and EGFR Regulation in Breast Cancer Cells by Vitamin D and Retinoid Compounds

The effect of 1,25-dihydroxyvitamin D(3), analog C (1,25-(OH)(2)-16-en-23-yn-26,27-F(6)-vitamin D(3)), 9-cis retinoic acid, and all-trans retinoic acid on the growth and expression of EGFR in MCF7, T47D, BT474, and BT549 breast cancer cells was examined. Significant growth inhibition was noted in MCF7, T47D, and BT474 cells by 8 days of treatment, while BT549 cells showed none. MCF7, T47D, and BT549 cells treated with 1,25-dihydroxyvitamin D(3) demonstrated a 50% decrease in EGFR mRNA within 2 h which was sustained to 72 h, while BT474 cells demonstrated a 200-500% increase. EGFR protein levels correlated with these mRNA changes in BT474 and BT549 cells. Measurement of mRNA stability in vitamin D treated BT474 cells indicated that there was no change in EGFR mRNA half-life. Transfection of an EGFR promoter containing reporter plasmid demonstrated vitamin D induced changes in reporter gene activity that paralleled the changes observed in EGFR mRNA and protein. Electrophoretic mobility shift assays using a putative vitamin D response element within this region of the EGFR promoter demonstrated specific VDR binding. These results indicate that the vitamin D effect on EGFR expression in breast cancer cells has a transcriptional component likely mediated through a vitamin D responsive promoter sequence. They also suggest that growth inhibition and EGFR down-regulation by vitamin D and retinoids may be related events in some breast cancer cells, but not in all.

Mechanisms implicated in the growth regulatory effects of vitamin D compounds in breast cancer cells

The active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25(OH)D3), has been recognized for over 2 decades as a modulator of cell proliferation and differentiation in many cell types, including breast cancer. However, any potential anti-tumour properties displayed by 1,25(OH)D3 are limited by the tendency to cause hypercalcaemia when administered at high doses. Because of this, synthetic vitamin D analogues have been developed that retain the anti-tumour effects seen with 1,25(OH)D3 but which have reduced calcaemic activity. However, it is still unclear as to how 1,25(OH)D3 and its synthetic analogues act within breast cancer cells to elicit the effects on cellular proliferation and differentiation. In this chapter we review the advances that have been made in trying to answer this question. It has been found so far that 1,25(OH)D3 has an effect on the expression of certain cell cycle regulators and in this way can bring about G1 arrest. Evidence has also emerged that vitamin D compounds can also affect the growth-promoting pathways initiated by two important factors involved in breast cancer cell promotion; namely the insulin-like growth factor I (IGF-I) and oestrogen-receptor (ER) pathways. Vitamin D compounds have also been implicated in promotion of apoptosis in breast cancer cells and evidence suggests that 1,25(OH)D3 and its synthetic analogues may potentiate responsiveness of breast cancer cells to conventional cytotoxic agents. Although much remains to be learned about the associated underlying mechanisms, ongoing research suggests that vitamin D analogues are a new class of compounds with potential in breast cancer treatment and prevention.

Modulation of growth factor/cytokine synthesis and signaling by 1alpha,25-dihydroxyvitamin D(3): implications in cell growth and differentiation

Distinct from its classic functions in the regulation of calcium and phosphorus metabolism as a systemic hormone, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is involved in the local control and regulation of cellular growth and differentiation in various tissues, including epidermis (keratinocytes) and bone (osteoblasts and osteoclasts). In this review, the impact of 1alpha,25(OH)(2)D(3) on growth factor/cytokine synthesis and signaling is discussed, particularly as it pertains to bone cells and keratinocytes. 1alpha,25(OH)(2)D(3) not only regulates growth factor/cytokine synthesis but may also alter growth factor signaling. Recently discovered examples for such interactions are the interactions between the vitamin D receptor and the mothers against decapentaplegic-related proteins that function downstream of TGFbeta receptors. Inhibitory effects of 1alpha,25(OH)(2)D(3) on keratinocytes through TGFbeta activation and IL-1alpha, IL-6, and IL-8 suppression may provide a rationale for its beneficial effects in the treatment of hyperproliferative skin disorders, whereas stimulatory effects through the epidermal growth factor-related family members and platelet-derived growth factor may be operative in its beneficial effects in skin atrophy and wound healing. Modulation of cytokines and growth factors by 1alpha,25(OH)(2)D(3) during bone remodeling plays an important role in the coupling of osteoblastic bone formation with osteoclastic resorption to maintain bone mass.

Mechanisms of the regulation of EGF receptor gene expression by calcitriol and parathyroid hormone in UMR 106-01 cells

BACKGROUND

We have previously demonstrated that parathyroid hormone (PTH) and calcitriol increase the expression of epidermal growth factor receptors (EGFR) in UMR 106-01 osteoblast-like cells. The effect of PTH is mediated by cAMP and it involves an increase in the level of EGFR mRNA. The present studies were designed to investigate the mechanisms involved in the regulation of EGFR expression by PTH and calcitriol.

METHODS

To examine the mechanism of the effect of calcitriol on EGFR expression, confluent cultures of UMR 106-01 cells were exposed to calcitriol and levels of EGFR mRNA were determined by reverse transcription-polymerase chain reaction (RT-PCR). In order to study the effect of calcitriol on EGFR gene transcription, a candidate vitamin D-responsive element (VDRE) was identified in the EGFR gene promoter and complimentary 30-mer oligonucleotides spanning this region were tested for binding to recombinant VDR using EMSA. Transcriptional activity in response to calcitriol and PTH was tested in UMR 106-01 cells stably transfected with a luciferase reporter construct containing the full length EGFR gene promoter. The effect of calcitriol on EGFR mRNA stability was examined in transcriptionally arrested cells.

RESULTS

Treatment with calcitriol resulted in a time and dose dependent increase in EGFR mRNA levels in confluent cultures of UMR 106-01 osteoblast-like cells. Using EMSA, we demonstrated that the putative human EGFR VDRE binds to recombinant VDR in a retinoid X receptor (RXR)-dependent manner; however, calcitriol failed to increase transcriptional activity from a luciferase reporter construct containing the full-length EGFR gene promoter in stably transfected UMR 106-01 cells. Therefore, EGFR mRNA degradation was examined in transcriptionally arrested cells and calcitriol was found to prolong the half life of EGFR mRNA. Treatment of the cultures with PTH resulted in a ninefold increase in luciferase activity after four hours of exposure, a finding that was reproduced by treatment with forskolin.

CONCLUSIONS

These studies demonstrate that the calciotropic hormones PTH and calcitriol increase EGF receptor expression by different mechanisms. The former increases EGFR gene transcription whereas the latter increases EGFR mRNA stability.

Growth regulation of human colon cancer cells by epidermal growth factor and 1,25-dihydroxyvitamin D3 is mediated by mutual modulation of receptor expression

The human colon adenocarcinoma-derived cell line Caco-2 was used as a model system to study the interaction of epidermal growth factors (EGF) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in control of colorectal cancer cell growth. The mitogenic stimulus of EGF was rapidly transduced via apical and basal membrane receptors alike into elevation of c-myc expression, causing a shift of Caco-2 cells from the G0/G1 into the S phase of the cell cycle. The stimulatory effect of EGF on cell division was effectively counteracted by 1,25(OH)2D3: the presence of the steroid hormone prevents the negative effect of EGF on vitamin D receptor abundance and concurrently minimises ligand-occupied EGF receptor numbers on both sides of Caco-2 cell monolayers. Our data suggest that EGF and 1,25-(OH)2D3 actions on mutual receptor levels represent a specific feature of the potent antimitogenic effect of the steroid hormone on colon cancer cells.

Regulation of a novel immediate early response gene, IEX-1, in keratinocytes by 1alpha,25-dihydroxyvitamin D3

1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3] regulates cellular growth and differentiation. We show that in keratinocytes, 1alpha, 25(OH)2D3 reduces concentrations of the messenger RNA of IEX-1, the product of which blocks Fas- or tumor necrosis factor type alpha-induced apoptosis in various cells. In sub-confluent keratinocyte cultures, the addition of 1alpha,25(OH)2D3, in amounts that induce growth arrest, reduces IEX-1 mRNA concentrations. In confluent cells, 1alpha,25(OH)2D3 initially reduces and then increases IEX-1 mRNA concentrations. IEX-1 protein is localized in the nucleus and perinuclear region of keratinocytes. In sub-confluent cells, 1alpha,25(OH)2D3 translocates IEX-1 protein from the nucleus to the perinuclear region and cytoplasm. Since IEX-1 has recently been shown to regulate cell survival and number, we suggest that IEX-1 may play a role in keratinocyte growth and differentiation and that 1alpha,25(OH)2D3 may reduce keratinocyte growth via a reduction in IEX-1 mRNA and a change in the intracellular distribution of IEX-1 protein.

1,25-dihydroxyvitamin D3 regulates the expression of N-myc, c-myc, protein kinase C, and transforming growth factor-beta2 in neuroblastoma cells

1alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3) alters the proliferation of neuroblastoma cells in culture in part via a nerve growth factor (NGF)-mediated pathway. This suggests that factors other than NGF also play a role in the growth arrest induced by 1,25(OH)2D3. To more fully characterize the effect of 1,25(OH)2D3 on neuroblastoma cells, we treated the cells with 10(-8) M 1,25(OH)2D3 and examined the cells for changes in the expression of N-myc, c-myc, transforming growth factor-beta2 (TGF-beta2), and protein kinase C (PKC) activity. Our results show that 1,25(OH)2D3 causes a decrease in the expression of N-myc and c-myc, as well as a two-fold increase in total PKC activity and a dose-dependent increase in TGF-beta2 expression. These results show that 1,25(OH)2D3 regulates the expression of growth-regulatory factors other than NGF in neuroblastoma cells and that 1,25(OH)2D3 influences the growth of neural cells via multiple growth regulatory pathways.

Effects of 1,25-dihydroxyvitamin D3 on growth of mouse neuroblastoma cells

Epitopes of the 1,25-dihydroxyvitamin D(1,25(OH)2D3) receptor have been shown in developing dorsal root ganglia in fetal mice, as well as in cells maintained in culture [Johnson, J.A., Grande, J.P., Windebank, A.J. and Kumar, R., 1,25-Dihydroxyvitamin D3 receptors in developing dorsal root ganglia of fetal rats, Dev. Brain Res., 92 (1996) 120-124]. To investigate a possible role for 1,25(OH)2D3 in neural cell growth and development, a murine neuroblastoma cell line that expresses 1,25(OH)2D3 receptors, was treated with 1,25(OH)2D3. Treatment with 1,25(OH)2D3 resulted in a decrease in cell proliferation, a change in cell morphology, and the expression of protein markers of mature neuronal cells. The decrease in cell proliferation was accompanied by an increase in the expression of nerve growth factor (NGF). Anti-NGF monoclonal antibody added to the growth medium blocked the decrease in cell proliferation caused by 1,25(OH)2D3 treatment. Our results show that the sterol hormone 1,25(OH)2D3, causes a decrease in the proliferation of mouse neuroblastoma cells through alterations in the expression of NGF.

Immunolocalization of vitamin D receptor and calbindin-D28k in human tooth germ

The role of vitamin D in ameloblasts and odontoblasts has been studied experimentally in rodents. Dental dysplasias have also been reported in clinical studies of children with rickets. Vitamin D acts via a nuclear receptor which binds the major metabolite, 1,25-dihydroxyvitamin D3, and positively or negatively controls the expression of specific genes. The most extensively studied markers of 1,25-dihydroxyvitamin D3 action are calbindin-D9k, calbindin-D28k, and osteocalcin. Therefore, to study in more detail the potential role of 1,25-dihydroxyvitamin D3 in human dental development, 1,25-dihydroxyvitamin D3 receptor (VDR) was localized by immunofluorescence in forming teeth (8-26 wk of gestation). Calbindin-D28k was also mapped by immunoperoxidase in antenatal and postnatal forming and formed teeth. VDR were detected in both dental epithelium and mesenchyme of bud, cap, and bell stages of tooth germs. Nuclei of overtly differentiated ameloblasts and odontoblasts were also immunostained. Calbindin-D28k was present in differentiated ameloblasts and odontoblasts. The presence of VDR and calbindin-D28k in ameloblasts and odontoblasts suggests that 1,25-dihydroxyvitamin D3 may contribute to the regulation of enamel and dentin formation, as classically reported for bone formation. Finally, the early appearance of VDR supports the concept that 1,25-dihydroxyvitamin D3 may also control forward stages of tooth crown development in humans.

EGF receptor expression, regulation, and function in breast cancer

Epidermal growth factor receptor (EGFR) overexpression correlates with both loss of estrogen receptor (ER) and poor prognosis in breast cancer. Interestingly, in normal breast EGFR appears to be expressed more frequently than in malignant tissue, and there may be a different relationship between ER and EGFR. A variety of cellular regulators, such as EGF, TGF alpha, phorbol esters, and steroid hormones, are capable of altering the level of EGFR expression in breast cells. However, much work remains to be done on the mechanistic details of EGFR regulation in this disease. The significance of EGFR as an oncogene in breast cancer is compounded by its potential interactions with other oncogenes such as c-erbB-2 and c-myc. Additionally, several recent studies have placed EGFR prominently in the signal transduction pathway, demonstrating that the EGFR-ligand system may play important roles throughout the course of malignant progression in breast cancer.

Analysis of epidermal growth factor receptor mRNA expression by polymerase chain reaction assay in 94 human breast adenocarcinoma tumors

It is well known that breast cancer cells can synthesize and secrete various growth factors that are able to stimulate tumor growth through autocrine and/or paracrine mechanisms. EGF is one of these growth factors involved in normal breast epithelial development and tumor proliferation. EGF and TGF alpha (EGF-like peptide) are produced in variable amounts and both bind to the EGF receptor (EGF-R). Previous investigation in the laboratory measuring free and occupied EGF-R sites by differential ligand binding assays had demonstrated that non-occupied and total binding sites were present in 54 and 90% of 216 breast tumor biopsies respectively. EGF-R appeared to be totally masked by endogenous ligand in 40 and 21% of estrogen receptor positive and negative tumors respectively. The aim of the present study was to check by a molecular method the expression of the EGF-R gene. The PCR method was applied to 94 tumor samples of the previous series. Total RNA was treated with 0.5 units of Rnase-free Dnase/mg of RNA to remove any contaminating DNA. We simultaneously reverse transcribed and amplified another transcript (beta-actin) as an internal standard. Both signals were present in 88 of the 94 samples while the presence of EGF-R was detected in 74 of them when assessed by radioligand assay. The findings indicate that 93% of the tumors analysed in this series expressed EGF-R mRNA, in agreement with our previous data on occupied EGF-R sites, i.e. two-fold more than by using the standard binding assay. No significant correlation was observed between the expression of the EGF-R gene and the estrogen receptor content.

Modulation of the immunophenotype of ovarian cancer cells by N,N-dimethylformamide and transforming growth factor-beta 1

Exposure of HOC-7 ovarian adenocarcinoma cells to regulators of cell differentiation caused inducer-dependent alterations of the antigenic pattern of the cells. Immunocytochemistry revealed that N,N-dimethylformamide (DMF) elevated the membrane staining for epidermal growth factor (EGF)-receptor and for desmoplakins I and II. DMF also stimulated cytoplasmic and surface labeling for CA 125 and the deposition of fibronectin into the extracellular matrix. Stimulation of fibronectin was also seen after addition of transforming growth factor (TGF)-beta 1. These responses were quantified using a fixed-cell, enzyme-linked immunosorbent assay (ELISA) and revealed that DMF dose-dependently induced expression of EGF-receptor, CA 125, fibronectin, and desmoplakins I and II. TGF-beta 1 stimulated fibronectin and desmoplakins I and II only. Production of EGF and TGF-alpha was not affected by these inducers. Immunocytochemistry, ELISA and Western blotting showed that both inducers caused down-regulation of myc oncoproteins. DMF was more effective in changing the immunophenotype of HOC-7 cells than TGF-beta 1. Desmoplakins I and II demonstrated elevated epithelial differentiation, whereas fibronectin indicated stimulation of extracellular matrix formation. Elevated EGF-receptor could not compensate for the growth inhibition induced by DMF. The expression of myc oncoproteins was inversely related to cell proliferation. CA 125, however, seems to be unrelated to cell growth.

Vitamin D3 and calcipotriol enhance the secretion of transforming growth factor-beta 1 and -beta 2 in cultured murine keratinocytes

Vitamin D3 and its analogue calcipotriol (MC 903) inhibit the proliferation of cultured keratinocytes and induce their differentiation. Since TGF beta s are very potent inhibitors of keratinocyte growth we studied the effects of vitamin D3 and calcipotriol on the secretion of TGF beta in cultured murine keratinocytes. Vitamin D3 and calcipotriol (10(-6)-10(-9) M) inhibited the DNA-synthesis of mouse keratinocytes by 50-80% in a time and dose-dependent manner as measured by [3H]-thymidine incorporation. Analysis of the conditioned medium of the keratinocytes indicated that the cells secreted into their medium activity that inhibited the growth of indicator Mv1Lu mink lung epithelial cells. Neutralizing antibodies against TGF beta 1 and TGF beta 2 decreased, and when used together, prevented the observed growth inhibition of the indicator cells. Heat treatment of the conditioned medium, which activates latent forms of TGF beta, revealed higher levels of growth inhibitory activity in the medium from vitamin D3 and calcipotriol treated than from control cultures indicating that a fraction of TGF beta was in a latent form. Active TGF beta was, however, detected considerably more in vitamin D3 and calcipotriol treated cultures than in control cultures. Immunoblotting analysis of the medium revealed enhanced secretion of TGF beta protein. These results indicate that enhanced TGF beta 1 and TGF beta 2 secretion and activity is associated with vitamin D3-mediated growth inhibition of cultured keratinocytes.

William L. McGuire Memorial Symposium. 1,25(OH)2D3 modulation of mammary tumor cell growth in vitro and in vivo

The biological role of 1,25(OH)2D3 in controlling Ca++ homeostasis in the body has been identified and widely investigated for a long time. More recently its effect in regulating cell proliferation or differentiated activity was described in a variety of normal and malignant cells. The present study was carried out to investigate the different aspects and biological mechanisms of this activity and to determine if the use of 1,25(OH)2D3 in the treatment of breast cancer patients could be considered. It is found that 1,25(OH)2D3 reduces the proliferation of MCF-7 and BT-20 cells lines regardless of their sex steroid receptor status. This effect is related to the concentration, from 10(-12) M to 10(-8) M. Its amplitude is less in other cell lines, but it opposes the EGF-induced increase of proliferation. It is observed that the proliferation rate of MCF-7 and BT-20 cells is increased when these tumor cells are cocultured with fibroblasts derived from breast tumor biopsies and that 1,25(OH)2D3 reverses this process. Moreover, experiments on DMBA induced mammary tumors in Sprague Dawley rats found that 1,25(OH)2D3 given at non toxic doses reduces significantly the tumor proliferation. These data showed that 1,25(OH)2D3 at low doses is effective on the proliferation of BT-20 and MCF-7 cells and on the paracrine growth stimulatory effect observed in the presence of fibroblasts. They suggest that 1,25(OH)2D3 or related synthetic molecules which are less active on Ca++ metabolism could be useful in the treatment of breast cancer patients.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, E.C. 1.2.1.12.) gene expression in two malignant human mammary epithelial cell lines: BT-20 and MCF-7. Regulation of gene expression by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key enzyme in the control of glycolysis. Its gene expression was analyzed in two breast cancer cell lines of human origin, BT-20 and MCF-7. We used a cDNA probe of 1.3 kb for Northern blot hybridization. It is found that GAPDH mRNA is overexpressed only in the poorly differentiated BT-20 cell line and that treatment of these cells by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) stimulates GAPDH mRNA expression in a dose-and time-dependent manner. The present investigation on the BT-20 cells indicates that the expression of GAPDH is sensitive to 1,25-(OH)2D3 and up-regulated by low doses of this steroid.