epidermal-growth-factor and inositol-1-4-bis(phosphate)

This study investigated the effects of epidermal growth factor (EGF) on cytosolic calcium ([Ca++]i) levels in rat calvarial osteoblasts, the nature of the regulation of this event, and the role these EGF-induced [Ca++]i changes have in osteoblastic cell proliferation. EGF significantly increased [Ca++]i measured in fura-2-loaded, individual cells. This increase was related to extracellular calcium influx. Activation of protein kinase C(PKC) by pretreating the cells with phorbol esters blocked the EGF-induced increase in [Ca++]i. EGF failed to increase inositol trisphosphate levels measured by high performance liquid chromatographic analysis. However, it did increase inositol bisphosphate and inositol tetrakisphosphate production. The EGF-dependent increase in DNA synthesis was partially blocked by the addition of calcium channel blockers. Therefore, it appears that the mechanism of action of EGF-induced osteoblastic cell proliferation is mediated by changes in [Ca++]i primarily due to extracellular calcium influx.

Topics: Analysis of Variance; Animals; Calcium; Calcium Channel Blockers; Cell Division; Cells, Cultured; Chromatography, High Pressure Liquid; Cytosol; DNA; Enzyme Activation; Epidermal Growth Factor; Fura-2; Inositol 1,4,5-Trisphosphate; Inositol Phosphates; Osteoblasts; Protein Kinase C; Rats; Rats, Sprague-Dawley; Tetradecanoylphorbol Acetate

Injection of D-myo-inositol-1,4,5-trisphosphate (IP3) was found to induce a transient increase of intracellular Ca2+ concentration in cancerous mammary cells (MMT060562) and in normal mammary cells treated with epidermal growth factor. Responses to injection of either D-myo-inositol-1,4-bisphosphate (IP2) or D-myo-inositol-1,3,4,5-tetrakisphosphate (IP4) were small or absent. Furthermore, normal mammary cells cultivated with low-protein serum replacement alone or in the presence of differentiation-inducing hormones (insulin + cortisol + prolactin) were less sensitive to IP3. Thapsigargin induced a transient increase of Ca2+ due to the release of Ca2+ from an intracellular pool. There was no difference in the peak heights of the thapsigargin-induced Ca2+ increase when mammary cells were cultivated in the presence or absence of epidermal growth factor or insulin + cortisol + prolactin. These findings suggest that the releasable intracellular Ca2+ pool remained unchanged whereas sensitivity to IP3 increases during the proliferation stage. Mechanical stimulus of a mammary cell induces an increase of intracellular Ca2+ in the stimulated cell. A certain stimulating factor is released from the mechanically stimulated cell into the extracellular space, and it induces an increase of Ca2+ in surrounding cells. In contrast, the IP3-induced Ca2+ increase in both cancerous and epidermal growth factor-treated normal mammary cells did not spread to adjacent cells. Therefore, increase of Ca2+ is not sufficient to account for the release of stimulating substances from mammary cells in the mechanically-induced spreading response.

Topics: Animals; Caffeine; Calcium; Cell Division; Cells, Cultured; Drug Resistance; Epidermal Growth Factor; Epithelial Cells; Epithelium; Female; Inositol 1,4,5-Trisphosphate; Inositol Phosphates; Mammary Glands, Animal; Mammary Neoplasms, Experimental; Mice; Mice, Inbred ICR; Pregnancy; Ryanodine; Terpenes; Thapsigargin; Tumor Cells, Cultured