Jones K T, Sharpe G R
Department of Dermatology, University of Liverpool, United Kingdom.
Exp Cell Res. 1994 Jan;210(1):71-6. doi: 10.1006/excr.1994.1011.
Thapsigargin raises intracellular free calcium ([Ca2+]i) by potently inhibiting the endoplasmic reticulum Ca-ATPase, which sequesters calcium from the cytosol. In human keratinocytes a rise in [Ca2+]i has been associated with differentiation and therefore we investigated the action of thapsigargin on this process. At concentrations above 3 nM thapsigargin inhibited keratinocyte proliferation. Thapsigargin induced an immediate transient [Ca2+]i rise in calcium-free or 70 microM calcium medium but a more prolonged rise in 2 mM calcium. For keratinocytes cultured in 70 microM calcium medium a late [Ca2+]i rise was also observed, after 6 h, similar to the effect of known differentiation stimuli. However, immunohistochemical techniques did not show any expression of the differentiation-specific protein involucrin, a component of the cornified envelope. When keratinocyte differentiation was induced by an increase in the extracellular calcium from 70 microM to 2 mM abundant involucrin and desmoplakin, a component of desmosomes, were synthesised. Both proteins gave staining patterns which suggested incorporation into structural proteins, but thapsigargin disrupted the calcium-induced pattern of involucrin and desmoplakin synthesis. Thapsigargin did not induce differentiation, possibly due to its inability to activate protein kinase C and raise inositol trisphosphate levels. We conclude that a rise in [Ca2+]i does not alone induce keratinocyte differentiation but may act with other intracellular signals to promote differentiation.
毒胡萝卜素通过强力抑制内质网钙 - ATP酶来提高细胞内游离钙浓度（[Ca2+]i），内质网钙 - ATP酶可从细胞质中隔离钙。在人类角质形成细胞中，[Ca2+]i的升高与分化相关，因此我们研究了毒胡萝卜素在此过程中的作用。浓度高于3 nM时，毒胡萝卜素会抑制角质形成细胞增殖。在无钙或70 microM钙的培养基中，毒胡萝卜素会立即引起[Ca2+]i短暂升高，但在2 mM钙的培养基中会引起更持久的升高。对于在70 microM钙培养基中培养的角质形成细胞，6小时后也观察到[Ca2+]i后期升高，类似于已知分化刺激的效果。然而，免疫组织化学技术未显示出分化特异性蛋白兜甲蛋白（一种角质包膜成分）的任何表达。当细胞外钙从70 microM增加到2 mM诱导角质形成细胞分化时，会合成大量的兜甲蛋白和桥粒斑蛋白（桥粒的一种成分）。这两种蛋白的染色模式表明它们被整合到结构蛋白中，但毒胡萝卜素破坏了钙诱导的兜甲蛋白和桥粒斑蛋白合成模式。毒胡萝卜素未诱导分化，可能是由于其无法激活蛋白激酶C和提高肌醇三磷酸水平。我们得出结论，[Ca2+]i的升高本身不会诱导角质形成细胞分化，但可能与其他细胞内信号共同作用来促进分化。
