Involvement of rho kinase in the ouabain-induced contractions of the rat renal arteries

The implication of ROCK 2 as a potential senotherapeutic target via the suppression of the harmful effects of the SASP: Do senescent cancer cells really engulf the other cells?

Chemotherapy-induced senescent cancer cells secrete several factors in their microenvironment called SASP. Accumulated evidence states that SASP is responsible for some of the harmful effects of chemotherapy such as drug resistance and the induction of cancer cell proliferation, migration, and invasion. Therefore, to develop senolytic and/or senomorphic drugs, targeting the senescent cells gains importance as a new strategy for preventing the damage that senescent cancer cells cause. In the current work, we evaluated whether Rho/Rho kinase pathway has the potential to be used as a target pathway for the development of senolytic and/or senomorphic drugs in doxorubicin-induced senescent cancer cell lines. We have determined that inhibition of Rho/Rho kinase pathway with CT04 and Y27632 reduced the secretory activity of senescent cancer cells and changed the composition of SASP. Our results indicate that ROCK 2 isoform was responsible for these observed effects on the SASP. In addition, non-senescent cancer cell proliferation and migration accelerated by senescent cells were set back to the pre-induction levels after ROCK inhibition. Moreover, contrary to the previous observations, another important finding of the current work is that senescent HeLa and A549 cells did not engulf the non-senescent HeLa, A549 cells, and non-cancer HUVEC. These results indicate that ROCK inhibitors, in particular ROCK 2 specific inhibitors, have the potential to be developed as novel senomorphic drugs. In addition, we found that all senescent cancer cells do not share the same engulfment ability, and this process should not be generalized.

Cardiac glycoside-induced cell death and Rho/Rho kinase pathway: Implication of different regulation in cancer cell lines

Previously, we demonstrated that the Rho/ROCK pathway is involved in ouabain-induced apoptosis in HUVEC. In the current work, we investigated whether the Rho/ROCK pathway is functional during cardiac glycosides-induced cytotoxic effects in cancer cell lines, as well as in non-tumor cells. For that purpose, we evaluated the role of ROCK activation in bleb formation and cell migration over upstream and downstream effectors in addition to ROCK cleavage after cardiac glycosides treatment. All three cardiac glycosides (ouabain, digoxin and bufalin) induced cell death in HeLa and HepG2 cells and increased the formation of blebbing in HeLa cells. In contrast to our previous study, ROCK inhibitor Y27632 did not prevent bleb formation. Observation of ROCK II cleavage after ouabain, digoxin and oxaliplatin treatments in HeLa and/or HepG2 cells suggested that cleavage is independent of cell type and cell death induction. While inhibiting cleavage of ROCK II by the caspase inhibitors z-VAD-fmk, z-VDVAD-fmk and z-DEVD-fmk, evaluation of caspase 2 siRNA ineffectiveness on this truncation indicated that caspase-dependent ROCK II cleavage is differentially regulated in cancer cell lines. In HeLa cells, ouabain induced the activation of ROCK, although it did not induce phosphorylation of ERM, an upstream effector. While Y27632 inhibited the migration of HeLa cells, 10nM ouabain had no effect on cell migration. In conclusion, these findings indicate that the Rho/ROCK pathway is regulated differently in cancer cell lines compared to normal cells during cardiac glycosides-induced cell death.

Chronic ouabain treatment induces Rho kinase activation

Ouabain is an endogenous Na(+)/K(+)-ATPase inhibitor whose chronic administration induces hypertension. Endogenous ouabain levels increase in human essential hypertension. On the other hand, Rho/Rho kinase (ROCK) pathway has been implicated in various animal models of hypertension. In the current work, we evaluated the possible involvement of Rho kinase in ouabain-induced hypertension. Ouabain was administered daily (20 µg/kg, i.p.) to Wistar rats for 6 weeks. After the ouabain treatment, we evaluated the possible changes in vascular responses to KCl and phenylephrine alone and in the presence of Rho kinase inhibitor Y27632. We also determined the expressions of ROCKs, Rho A and phosphorylation of myosin binding subunit of myosin light chain phosphatase (pMYPT) and activation of Rho A. Agonist-induced contractions in the presence of Y27632 are significantly decreased and Y27632-induced relaxations in aortas precontracted with phenylephrine are significantly enhanced with the chronic treatment of ouabain. Although the expressions of ROCK I and ROCK II remained unchanged, pMYPT expression was significantly increased in ouabain-treated group. Moreover, Rho A expression and activation were decreased after treatment with ouabain. Although Rho kinase expression did not change in aortas, increased basal Rho kinase activation may contribute to the development of ouabain-induced hypertension. Our current data present the first evidence that Rho kinase is involved in the development of ouabain-induced hypertension in rats.

Extracellular signal-regulated kinase and GEF-H1 mediate depolarization-induced Rho activation and paracellular permeability increase

Plasma membrane depolarization activates the Rho/Rho kinase (ROK) pathway and thereby enhances myosin light chain (MLC) phosphorylation, which in turn is thought to be a key regulator of paracellular permeability. However, the upstream mechanisms that couple depolarization to Rho activation and permeability changes are unknown. Here we show that three different depolarizing stimuli (high extracellular K(+) concentration, the lipophilic cation tetraphenylphosphonium, or l-alanine, which is taken up by electrogenic Na(+) cotransport) all provoke robust phosphorylation of ERK in LLC-PK1 and Madin-Darby canine kidney (MDCK) cells. Importantly, inhibition of ERK prevented the depolarization-induced activation of Rho. Searching for the underlying mechanism, we have identified the GTP/GDP exchange factor GEF-H1 as the ERK-regulated critical exchange factor responsible for the depolarization-induced Rho activation. This conclusion is based on our findings that 1) depolarization activated GEF-H1 but not p115RhoGEF, 2) short interfering RNA-mediated GEF-H1 silencing eliminated the activation of the Rho pathway, and 3) ERK inhibition prevented the activation of GEF-H1. Moreover, we found that the Na(+)-K(+) pump inhibitor ouabain also caused ERK, GEF-H1, and Rho activation, partially due to its depolarizing effect. Regarding the functional consequences of this newly identified pathway, we found that depolarization increased paracellular permeability in LLC-PK1 and MDCK cells and that this effect was mitigated by inhibiting myosin using blebbistatin or a dominant negative (phosphorylation incompetent) MLC. Taken together, we propose that the ERK/GEF-H1/Rho/ROK/pMLC pathway could be a central mechanism whereby electrogenic transmembrane transport processes control myosin phosphorylation and regulate paracellular transport in the tubular epithelium.

Pharmacological characterization of SAR407899, a novel rho-kinase inhibitor

Recent advances in basic and clinical research have identified Rho kinase as an important target potentially implicated in a variety of cardiovascular diseases. Rho kinase is a downstream mediator of RhoA that leads to stress fiber formation, membrane ruffling, smooth muscle contraction, and cell motility. Increased Rho-kinase activity is associated with vasoconstriction and elevated blood pressure. We identified a novel inhibitor of Rho kinase (SAR407899) and characterized its effects in biochemical, cellular, tissue-based, and in vivo assays. SAR407899 is an ATP-competitive Rho-kinase inhibitor, equipotent against human and rat-derived Rho-kinase 2 with inhibition constant values of 36 nM and 41 nM, respectively. It is highly selective in panel of 117 receptor and enzyme targets. SAR407899 is approximately 8-fold more active than fasudil. In vitro, SAR407899 demonstrated concentration-dependent inhibition of Rho-kinase-mediated phosphorylation of myosin phosphatase, thrombin-induced stress fiber formation, platelet-derived growth factor-induced proliferation, and monocyte chemotactic protein-1-stimulated chemotaxis. SAR407899 potently (mean IC(50) values: 122 to 280 nM) and species-independently relaxed precontracted isolated arteries of different species and different vascular beds. In vivo, over the dose range 3 to 30 mg/kg PO, SAR407899 lowered blood pressure in a variety of rodent models of arterial hypertension. The antihypertensive effect of SAR407899 was superior to that of fasudil and Y-27632. In conclusion, SAR407899 is a novel and potent selective Rho-kinase inhibitor with promising antihypertensive activity.