Role of STIM1-and Orai1-mediated Ca2+ entry in Ca2+-induced epidermal keratinocyte differentiation

Journal of Cell Science (Impact Factor: 5.33). 11/2012; 126(2). DOI: 10.1242/jcs.115980
Source: PubMed

ABSTRACT The barrier function of skin is due to the thin layer on the uppermost surface of the skin called the epidermis. The epidermis has a multilayered structure in which each layer consists of keratinocytes (KCs) of different differentiation status. The integrity of KC differentiation is critical for the function of skin and its abrogation causes or is accompanied by skin diseases. Intracellular and extracellular Ca(2+) are known to play important roles in KC differentiation. However, the molecular mechanisms underlying Ca(2+)-regulation of KC differentiation are still largely unknown. Store-operated Ca(2+) entry (SOCE) is a major Ca(2+) influx pathway in most non-excitable cells. SOCE is evoked in response to a fall in [Ca(2+)] in the endoplasmic reticulum (ER). Two proteins have been identified as essential components of SOCE: STIM1, a Ca(2+) sensor in the ER, and Orai1, a subunit of Ca(2+) channels in the plasma membrane. In this study, we analyzed the contribution of SOCE to KC growth and differentiation using RNAi knockdown of STIM1 and Orai1 in the human keratinocyte cell line, HaCaT. KC differentiation was induced by a switch in extracellular Ca(2+) concentration from low (0.03 mM; undifferentiated KCs) to high (1.8 mM; differentiated KCs). This Ca(2+) switch triggers phospholipase C-mediated intracellular Ca(2+) signals (Ca(2+)-switch-induced Ca(2+) response), which would likely involve the activation of SOCE. Knockdown of either STIM1 or Orai1 strongly suppressed SOCE and almost completely abolished the Ca(2+)-switch-induced Ca(2+) responses, resulting in impaired expression of keratin1, an early KC differentiation marker. Furthermore, loss of either STIM1 or Orai1 suppressed normal growth of HaCaT cells in low Ca(2+) condition and inhibited the growth arrest in response to Ca(2+) switch. These results demonstrate that SOCE plays multiple critical roles in KC differentiation and function.

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