Polarized but Differential Localization and Recruitment of STIM1, Orai1 and TRPC Channels in Secretory Cells |
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Authors: | Jeong Hee Hong Qin Li Min Seuk Kim Dong Min Shin Stefan Feske Lutz Birnbaumer Kwong Tai Cheng Indu S. Ambudkar Shmuel Muallem |
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Affiliation: | 1. Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA;2. Molecular Physiology and Therapeutics Branch, NIDCR, NIH, Bethesda, MD 20892, USA;3. The Department of Oral Biology, Brain Korea 21 Project, Yonsei University College of Dentistry, Seoul 120‐752, Korea;4. New York University Langone Medical Center, New York, NY 10016, USA;5. Laboratory of Neurobiology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA |
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Abstract: | Polarized Ca2+ signals in secretory epithelial cells are determined by compartmentalized localization of Ca2+ signaling proteins at the apical pole. Recently the ER Ca2+ sensor STIM1 (stromal interaction molecule 1) and the Orai channels were shown to play a critical role in store‐dependent Ca2+ influx. STIM1 also gates the transient receptor potential‐canonical (TRPC) channels. Here, we asked how cell stimulation affects the localization, recruitment and function of the native proteins in polarized cells. Inhibition of Orai1, STIM1, or deletion of TRPC1 reduces Ca2+ influx and frequency of Ca2+ oscillations. Orai1 localization is restricted to the apical pole of the lateral membrane. Surprisingly, cell stimulation does not lead to robust clustering of native Orai1, as is observed with expressed Orai1. Unexpectedly, cell stimulation causes polarized recruitment of native STIM1 to both the apical and lateral regions, thus to regions with and without Orai1. Accordingly, STIM1 and Orai1 show only 40% colocalization. Consequently, STIM1 shows higher colocalization with the basolateral membrane marker E‐cadherin than does Orai1, while Orai1 showed higher colocalization with the tight junction protein ZO1. TRPC1 is expressed in both apical and basolateral regions of the plasma membrane. Co‐IP of STIM1/Orai1/IP3 receptors (IP3Rs)/TRPCs is enhanced by cell stimulation and disrupted by 2‐aminoethoxydiphenyl borate (2APB). The polarized localization and recruitment of these proteins results in preferred Ca2+ entry that is initiated at the apical pole. These findings reveal that in addition to Orai1, STIM1 likely regulates other Ca2+ permeable channels, such as the TRPCs. Both channels contribute to the frequency of [Ca2+] oscillations and thus impact critical cellular functions. |
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Keywords: | epithelial cells Orai1 polarized recruitment STIM1 TRPC1 |
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