epidermal-growth-factor and maxacalcitol

PTH-related peptide (PTHrP) mediates the syndrome of humoral hypercalcemia of malignancy, a frequent complication of squamous cell carcinomas of the lung. This study was undertaken to determine whether 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and two nonhypercalcemic analogs, EB1089 and 22-oxa-1,25-(OH)2D3 (22-oxacalcitriol), suppress serum- and epidermal growth factor (EGF)-induced PTHrP gene expression in a human lung squamous cancer cell line, NCI H520. PTHrP expression was up-regulated by serum and EGF in a concentration- and time-dependent manner. Nuclear run-on analysis showed that this induction was mediated via a transcriptional mechanism, and that sequences within promoter 1 were responsible. All three vitamin D3 compounds decreased both basal and serum- and EGF-induced steady state PTHrP messenger RNA and secreted peptide levels. These effects were again mediated via a transcriptional mechanism through sequences within promoter 1. All three vitamin D3 compounds also decreased the proliferation of NCI H520 cells in a concentration- and time-dependent manner. 1,25-(OH)2D3 is hypercalcemic in vivo. However, the noncalcemic analogs EB1089 and 22-oxa-1,25-(OH)2D3 have therapeutic potential, as they suppress not only the basal but also the growth factor-stimulated levels of PTHrP in a cancer cell line associated with hypercalcemia.

Topics: Blood Physiological Phenomena; Calcitriol; Cell Division; Epidermal Growth Factor; Gene Expression Regulation; Humans; Lung Neoplasms; Parathyroid Hormone-Related Protein; Promoter Regions, Genetic; Proteins; Tumor Cells, Cultured

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] is known to influence cell proliferation/maturation, whereas epidermal growth factor (EGF) is a potent stimulant of proliferation. Recently, hypocalcemia of vitamin D (D) deficiency was shown to significantly perturbe hepatic regeneration, which could be only partly restored by normalizing extracellular calcium, whereas normalization of 1,25-(OH)2D3 fully restored the process. To define the calcium- and/or D3-sensitive mechanisms associated with liver growth, a study of the initial events transduced by EGF was initiated by probing EGF receptor (EGFR) density and affinity, its subsequent autophosphorylation, and the level of its steady state transcript. Studies were carried out in D-depleted rats kept either untreated or supplemented with D3, 1,25-(OH)2D3, or calcium alone. The hepatic EGFR number (picomoles per mg microsomal protein) was significantly affected by hypocalcemic D-depleted (0.82 +/- 0.2), but responded with similar increases to calcium (1.7 +/- 0.09; P < 0.05), D3 (1.6 +/- 0.3; P < 0.05), and 1,25-(OH)2D3 (2.1 +/- 0.3; P < 0.01). The EGFR mRNA level revealed, however, no significant effect of the calcium or D3 status, indicating that posttranscriptional events were playing an important role. Phosphorylation studies showed that EGFR autophosphorylation and tyrosine protein kinase activity paralleled receptor density, with the lowest autophosphorylation values obtained in hypocalcemic D-depleted rats (D-depleted hypocalcemic vs. D3 repleted, P < 0.007). When normalized for receptor number, however, EGFR autophosphorylation increased in D-depleted hypocalcemic rats to a level comparable to that observed in all other groups. To dissociate the effect of the D3 hormone from that of calcium alone on EGFR, D-depleted rats were treated with the nonhypercalcemic 1,25-(OH)2D3 analog 22-OXA-1,25-(OH)2D3 (OCT), with or without calcium supplementation. Hypocalcemic OCT-treated rats did not exhibit any increase in EGFR number (0.6 +/- 0.1) compared to D-depleted hypocalcemic rats, but the addition of dietary calcium to OCT restored extracellular calcium concentrations and EGFR density (1.8 +/- 0.2; P < 0.002) to values comparable to those observed after D3 or 1,25-(OH)2D3 treatment. EGFR autophosphorylation was also decreased in hypocalcemic OCT-treated animals (P < 0.03), but after normalization for receptor density, full restoration of EGFR autophosphorylation was achieved. Our data demonstrate that in normal hepat

Topics: Animals; Calcitriol; Calcium; Cholecalciferol; Epidermal Growth Factor; ErbB Receptors; Female; Hypocalcemia; Liver; Male; Phosphorylation; Rats; Rats, Sprague-Dawley; RNA, Messenger; Transforming Growth Factor alpha; Vitamin D Deficiency