Abstract
The tight junctional pore-forming protein claudin-2 (CLDN-2) mediates paracellular Na+ and water transport in leaky epithelia and alters cancer cell proliferation. Previously, we reported that tumor necrosis factor-α time-dependently alters CLDN-2 expression in tubular epithelial cells. Here, we found a similar expression pattern in a mouse kidney injury model (unilateral ureteral obstruction), consisting of an initial increase followed by a drop in CLDN-2 protein expression. CLDN-2 silencing in LLC-PK1 tubular cells induced activation and phosphorylation of guanine nucleotide exchange factor H1 (GEF-H1), leading to Ras homolog family member A (RHOA) activation. Silencing of other claudins had no such effects, and re-expression of an siRNA-resistant CLDN-2 prevented RHOA activation, indicating specific effects of CLDN-2 on RHOA. Moreover, kidneys from CLDN-2 knockout mice had elevated levels of active RHOA. Of note, CLDN-2 silencing reduced LLC-PK1 cell proliferation and elevated expression of cyclin-dependent kinase inhibitor P27 (P27KIP1) in a GEF-H1/RHOA-dependent manner. P27KIP1 silencing abrogated the effects of CLDN-2 depletion on proliferation. CLDN-2 loss also activated myocardin-related transcription factor (MRTF), a fibrogenic RHOA effector, and elevated expression of connective tissue growth factor and smooth muscle actin. Finally, CLDN-2 down-regulation contributed to RHOA activation and smooth muscle actin expression induced by prolonged tumor necrosis factor-α treatment, because they were mitigated by re-expression of CLDN-2. Our results indicate that CLDN-2 suppresses GEF-H1/RHOA. CLDN-2 down-regulation, for example, by inflammation, can reduce proliferation and promote MRTF activation through RHOA. These findings suggest that the initial CLDN-2 elevation might aid epithelial regeneration, and CLDN-2 loss could contribute to fibrotic reprogramming.
Highlights
The tight junctional pore-forming protein claudin-2 (CLDN-2) mediates paracellular Na؉ and water transport in leaky epithelia and alters cancer cell proliferation
We have previously shown that in cultured tubular cells TNF␣ altered expression of the channel forming Tight junctions (TJ) protein CLDN-2 in a biphasic manner, with an initial increase followed by a drop [19]
CLDN-2 loss induced by cytokines can lead to guanine nucleotide exchange factor H1 (GEF-H1)– dependent Ras homolog family member A (RHOA) activation, which mediates up-regulation of the cyclin-dependent kinase inhibitors (CDKI) P27KIP1 to reduce proliferation
Summary
The tight junctional pore-forming protein claudin-2 (CLDN-2) mediates paracellular Na؉ and water transport in leaky epithelia and alters cancer cell proliferation. CLDN-2 down-regulation, for example, by inflammation, can reduce proliferation and promote MRTF activation through RHOA These findings suggest that the initial CLDN-2 elevation might aid epithelial regeneration, and CLDN-2 loss could contribute to fibrotic reprogramming. A family of 27 small, tetraspan membrane proteins are an integral part of the TJs and are expressed in a tissuespecific manner [10] They bind their counterparts in neighboring cells in homo- and heterotypic interactions and seal off the paracellular space. The cytoplasmic tail of claudins binds PDZ domain– containing adapter proteins [11] These adapters generate multiprotein complexes that link claudins to the junctional actomyosin ring, which contributes to dynamic TJ regulation [3]. The exact mechanistic details of such noncanonical functions remain incompletely understood
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
