Evidence that TRPC1 contributes to calcium-induced differentiation of human keratinocytes

Abstract

External calcium ion concentration is a major regulator of epidermal keratinocyte differentiation in vitro and probably also in vivo. Regulation of calcium-induced differentiation changes is proposed to occur via an external calcium-sensing, signaling pathway that utilizes increases in intracellular calcium ion concentration to activate differentiation-related gene expression. Calcium ion release from intracellular stores and calcium ion influx via store-operated calcium-permeable channels are key elements in this proposed signaling pathway; however, the channels involved have not yet been identified. The present report shows that human gingival keratinocytes (HGKs) also undergo calcium-induced differentiation in vitro as indicated by involucrin expression and morphological changes. Moreover, TRPC1, which functions as a store-operated calcium channel in a number of cell types, including epidermal keratinocytes, is expressed in both proliferating and differentiating HGKs. Transfection of HGKs with TRPC1 siRNA disrupted expression of TRPC1 mRNA and protein compared with transfection with scrambled TRPC1 siRNA. Cells with disrupted TRPC1 expression showed decreased calcium-induced differentiation as measured by involucrin expression or morphological changes, as well as decreased thapsigargin-induced calcium ion influx, and a decreased rate of store calcium release. These results indicate that TRPC1 is involved in calcium-induced differentiation of HGKs likely by supporting a store-operated calcium ion influx.

Defective channels lead to an impaired skin barrier

“…A number of the 'classical' TRPC subfamily channels (so called as they were the first identified members of the TRP superfamily) are expressed in the epidermis, and there is evidence that the TRPC channels might have a key role in promoting Ca 2+ -induced keratinocyte differentiation and, hence, barrier formation (Cai et al, 2006;Beck et al, 2008;Müller et al, 2008). Extracellular Ca 2+ is crucial for the regulation of the process of keratinocyte differentiation (Sharpe et al, 1989;Pillai et al, 1990), and a Ca 2+ gradient is seen in the epidermis, with the lowest concentrations found in the proliferating basal layer and the highest concentrations in the upper differentiating granular layer (Menon et al, 1985).…”

“…A major Ca 2+ entry route into cells is the store-operated route, whereby an increase in the concentration of extracellular Ca 2+ is detected and leads to the release of Ca 2+ from internal stores, such as the ER and Golgi, within the cell, which in turn activates store-operated calcium (SOC) channels in the plasma membrane, allowing an influx of extracellular Ca 2+ and increasing the intracellular Ca 2+ concentration to a level required to induce differentiation. TRPC1 and TRPC4 have been demonstrated to act as SOC channels in Ca 2+ -induced differentiation of human keratinocytes in vitro (Tu et al, 2005;Cai et al, 2006;Beck et al, 2008). Moreover, the importance of TRPC channels in keratinocyte differentiation is highlighted by the finding that activation of TRPC6 is sufficient to induce in vitro keratinocyte differentiation to levels similar to those seen when the cells are stimulated with high concentrations of extracellular Ca 2+ (Müller et al, 2008).…”

Darier’s disease: a calcium-signaling perspective

“…SERCA pumps perform the crucial function of replenishing the depleted ER Ca 2+ stores and hence constitute an integral component of the cellular Ca 2+ homeostasis circuitry [29]. The potential role of Ca 2+ in the growth and differentiation of epithelial cells as well as keratinocytes is recognized [3,5,30]. Interestingly, the majority of SERCA2 mutations associated with classical DD reveal a reduction in the expression and activity of the pump [15][16][17][18][19][20].…”

“…Darier's disease -TRPC1 perspective TRPC1, which is typically activated by ER store depletion, has been reported to be a critical component of SOCs in many cell types including endothelial, neuronal, smooth muscle and salivary gland cells, platelets, and keratinocytes [30,35,36,38,44,45]. Its interactions with the newly identified SOCE components, STIM1 and ORAI1, as a dynamic complex further amplify the physiological significance of TRPC1 as a SOC [41,46,47].…”

TRP Channels and Pruritus

“…TRPC channels are important regulators of intracellular calcium homeostasis in several cells types [47,154,362,363]. Epidermal or mucosal keratinocytes also express various TRPC channels (TRPC1, TRPC4, TRPC5, TRPC6, TRPC7), and their expression levels fluctuate in a differentiationdependent manner [364][365][366].…”