ABSTRACT
Intracellular calcium signaling is critical for initiating and sustaining diverse cellular functions including transcription, synaptic signaling, muscle contraction, apoptosis and fertilization. Trans-membrane 203 (TMEM203) was identified here in cDNA overexpression screens for proteins capable of modulating intracellular calcium levels using activation of a calcium/calcineurin regulated transcription factor as an indicator. Overexpression of TMEM203 resulted in a reduction of Endoplasmic Reticulum (ER) calcium stores and elevation in basal cytoplasmic calcium levels. TMEM203 protein was localized to the ER and found associated with a number of ER proteins which regulate ER calcium entry and efflux. Mouse Embryonic Fibroblasts (MEFs) derived from Tmem203 deficient mice had reduced ER calcium stores and altered calcium homeostasis. Tmem203 deficient mice were viable though male knockout mice were infertile and exhibited a severe block in spermiogenesis and spermiation. Expression profiling studies showed significant alternations in expression of calcium channels and pumps in testes and concurrently Tmem203 deficient spermatocytes demonstrated significantly altered calcium handling. Thus Tmem203 is an evolutionarily conserved regulator of cellular calcium homeostasis, is required for spermatogenesis and provides a causal link between intracellular calcium regulation and spermiogenesis.
Subject(s)
Calcium/metabolism , Homeostasis , Membrane Proteins/genetics , Membrane Proteins/metabolism , Spermatogenesis , Animals , Calcineurin/metabolism , Calcium Signaling , Cell Line , Endoplasmic Reticulum/metabolism , Epididymis/metabolism , Epididymis/pathology , Female , Gene Expression , Gene Expression Regulation , Humans , Infertility, Male/genetics , Infertility, Male/metabolism , Intracellular Space/metabolism , Male , Mice , Mice, Knockout , Protein Binding , Transcription Factors/metabolismABSTRACT
The CREB family of proteins are critical mediators of gene expression in response to extracellular signals and are essential regulators of adaptive behavior and long-term memory formation. The TORC proteins were recently described as potent CREB coactivators, but their role in regulation of CREB activity remained unknown. TORC proteins were found to be exported from the nucleus in a CRM1-dependent fashion. A high-throughput microscopy-based screen was developed to identify genes and pathways capable of inducing nuclear TORC accumulation. Expression of the catalytic subunit of PKA and the calcium channel TRPV6 relocalized TORC1 to the nucleus. Nuclear accumulation of the three human TORC proteins was induced by increasing intracellular cAMP or calcium levels. TORC1 and TORC2 translocation in response to calcium, but not cAMP, was mediated by calcineurin, and TORC1 was shown to be directly dephosphorylated by calcineurin. TORC function was shown to be essential for CRE-mediated gene expression induced by cAMP, calcium, or GPCR activation, and nuclear transport of TORC1 was sufficient to activate CRE-dependent transcription. Drosophila TORC was also shown to translocate in response to calcineurin activation in vivo. Thus, TORC nuclear translocation is an essential, conserved step in activation of cAMP-responsive genes.
