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Inter-organelle membrane contact sites (MCSs) are classically defined as areas of close proximity between heterologous membranes and established by specific proteins (termed tethers). The interest on MCSs has rapidly increased in the last years, since MCSs play a crucial role in the transfer of cellular components between different organelles and have been involved in important cellular functions such as apoptosis, organelle division and biogenesis, and cell growth. Recently, an unprecedented depth and breadth in insights into the details of MCSs have been uncovered. On one hand, extensive MCSs (organelles interactome) are revealed by comprehensive analysis of organelle network with high temporal-spatial resolution at the system level. On the other hand, more and more tethers involving in MCSs are identified and further works are focusing on addressing the role of these tethers in regulating the function of MCSs at the molecular level. These enormous progresses largely depend on the powerful approaches, including several different types of microscopies and various biochemical techniques. These approaches have greatly accelerated recent advances in MCSs at the system and molecular level. In this review, we summarize the current and emerging approaches for studying MCSs, such as various microscopies, proximity-driven fluorescent signal generation and proximity-dependent biotinylation. In addition, we highlight the advantages and disadvantages of the techniques to provide a general guidance for the study of MCSs.

We have reported that the bacterial LPS induces the activation of NF-κB and inflammatory cytokine gene expression and that this requires the activity of small GTPase, RhoA. In this study, we show that an atypical protein kinase C isozyme, PKCζ, associates functionally with RhoA and that PKCζ acts as a signaling component downstream of RhoA. Stimulation of monocytes and macrophages with LPS resulted in PKCζ activation and that inhibition of PKCζ activity blocks both LPS-stimulated activation of NF-κB and IL-1β gene expression. Our results also indicate that transforming growth factor β-activated kinase 1 acts as a signaling component downstream of PKCζ in cytokine gene transcription stimulated by LPS in human peripheral blood monocytes and macrophages. The specificity of this response suggests an important role for the Rho GTPase/PKCζ/transforming growth factor β-activated kinase 1/NF-κB pathway in host defense and in proinflammatory cytokine synthesis induced by bacterial LPS.

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