Activation of the cGMP/protein kinase G system in breast cancer by the dopamine receptor-1

Despite recent advances in the detection and treatment of breast cancer,many shortcomings remain,providing incentives to search for new therapeutic targets.This review provides information on the expression and actions of dopamine receptor-1(D1R)in breast cancer.D1R is overexpressed in a significant number of primary breast tumors,characterized by having an aggressive phenotype and predicting a shorter survival time for patients.Activation of D1R in breast cancer cells by selective agonists caused suppression of cell viability,stimulation of apoptosis,inhibition of cell invasion,and an increase in chemosensitivity.Instead of being linked to the cAMP/PKA system as expected,D1R in breast cancer is linked to the activation of the cGMP/protein kinase G(PKG)pathway.Fenoldopam,a peripheral D1R agonist that does not penetrate the brain,dramatically suppressed the growth of breast cancer xenografts in immune-deficient mice.A new imaging system for detecting D1R-expressing tumors and metastases was also developed.The review offers a novel concept that D1R can serve as a biomarker for prognosis in advanced breast cancer and its agonists can be used as effective and personalized therapeutics in a subpopulation of patients with D1R-expressing breast tumors.Several drugs,some of which are FDA-approved,that bypass the D1R and directly activate the cGMP/PKG apoptotic system,are also identified.

Targeting the nitric oxide/cGMP signaling pathway to treat chronic pain

Nitric oxide(NO)/cyclic guanosine 3′,5′-monophosphate(cGMP) signaling has been shown to act as a mediator involved in pain transmission and processing. In this review, we summarize and discuss the mechanisms of the NO/cGMP signaling pathway involved in chronic pain, including neuropathic pain, bone cancer pain, inflammatory pain, and morphine tolerance. The main process in the NO/cGMP signaling pathway in cells involves NO activating soluble guanylate cyclase, which leads to subsequent production of cGMP. cGMP then activates cGMP-dependent protein kinase(PKG), resulting in the activation of multiple targets such as the opening of ATP-sensitive K+ channels. The activation of NO/cGMP signaling in the spinal cord evidently induces upregulation of downstream molecules, as well as reactive astrogliosis and microglial polarization which participate in the process of chronic pain. In dorsal root ganglion neurons, natriuretic peptide binds to particulate guanylyl cyclase, generating and further activating the cGMP/PKG pathway, and it also contributes to the development of chronic pain. Upregulation of multiple receptors is involved in activation of the NO/cGMP signaling pathway in various pain models. Notably the NO/cGMP signaling pathway induces expression of downstream effectors, exerting both algesic and analgesic effects in neuropathic pain and inflammatory pain. These findings suggest that activation of NO/cGMP signaling plays a constituent role in the development of chronic pain, and this signaling pathway with dual effects is an interesting and promising target for chronic pain therapy.

Glabridin Relaxes Vascular Smooth Muscles by Activating BK_(Ca) Channels and Inhibiting Phosphodiesterase in Human Saphenous Vein

The aim of the current study was to investigate the pharmacological activity of glabridinon the isolated human saphenous vein (SV) and explore the underlying mechanisms. Samples of patients' SVs were removed during bypass surgery, and 4-mm lengths of the vessels were placedin Krebs solution at ±4℃ and hung in an isolated organ bath to assess their contraction/relaxationresponses. The contraction/relaxation responses were recorded to observe if the cyclic guanosinemonophosphate (cGMP)/protein kinase G (PKG) pathway mediates the relaxant effect of glabridinafter treatment with blockers like ODQ (a guanylate cyclase inhibitor), KT5823 (a PKG inhibitor),isobutylmethylxanthine [IBMX, a phosphodiesterase (PDE) inhibitor], and cantharidin [Cant,a myosin light-chain phosphatase (MLCP) inhibitor]. Moreover, nitric oxide (NO), cGMP, andPKG levels in SV tissues were determined by ELISA after incubation with glabridin, N(o)-nitro-L-arginine methyl ester (L-Name, a NO synthetase inhibitor), phenylephrine (PE), ODQ, IBMX,and KT5823. The results showed that glabridin relaxed the vascular smooth muscle of humanSV pretreated with PE in a dose-dependent manner, which was independent of the endothelium.The vasorelaxant effect of glabridin was only inhibited by iberiotoxin (IbTX), Cant, and KT5823.Glabridin increased cGMP and PKG levels in SV homogenates, whereas it did not alter the NOlevel. The enhancing efects of cGMP and PKG levels by glabridin were abolished by ODQ andKT5823. In conclusion, glabridin has a vasorelaxant effect, which is associated with the activationof BKc. channels and inhibition of PDE.

Targeted inhibition of GRK2 kinase domain by CP-25 to reverse fibroblast-like synoviocytes dysfunction and improve collagen-induced arthritis in rats

Rheumatoid arthritis(RA)is an autoimmune disease and is mainly characterized by abnormal proliferation of fibroblast-like synoviocytes(FLS).The up-regulated cellular membrane expression of G protein coupled receptor kinase 2(GRK2)of FLS plays a critical role in RA progression,the increase of GRK2 translocation activity promotes dysfunctional prostaglandin E4 receptor(EP4)signaling and FLS abnormal proliferation.Recently,although our group found that paeoniflorin-6’-O-benzene sulfonate(CP-25),a novel compound,could reverse FLS dysfunction via GRK2,little is known as to how GRK2 translocation activity is suppressed.Our findings revealed that GRK2 expression up-regulated and EP4 expression down-regulated in synovial tissues of RA patients and collagen-induced arthritis(CIA)rats,and prostaglandin E2(PGE2)level increased in arthritis.CP-25 could down-regulate GRK2 expression,up-regulate EP4 expression,and improve synovitis of CIA rats.CP-25 and GRK2 inhibitors(paroxetine or GSK180736 A)inhibited the abnormal proliferation of FLS in RA patients and CIA rats by down-regulating GRK2 translocation to EP4 receptor.The results of microscale thermophoresis(MST),cellular thermal shift assay,and inhibition of kinase activity assay indicated that CP-25 could directly target GRK2,increase the protein stability of GRK2 in cells,and inhibit GRK2 kinase activity.The docking of CP-25 and GRK2 suggested that the kinase domain of GRK2 might be an important active pocket for CP-25.G201,K220,K230,A321,and D335 in kinase domain of GRK2 might form hydrogen bonds with CP-25.Site-directed mutagenesis and co-immunoprecipitation assay further revealed that CP-25 down-regulated the interaction of GRK2 and EP4 via controlling the key amino acid residue of Ala321 of GRK2.Our data demonstrate that FLS proliferation is regulated by GRK2 translocation to EP4.Targeted inhibition of GRK2 kinase domain by CP-25 improves FLS function and represents an innovative drug for the treatment of RA by targeting GRK2.

Banxia Xiexin Decoction(半夏泻心汤)Treats Diabetic Gastroparesis through PLC-IP3-Ca^2+/NO-cGMP-PKG Signal Pathway

Objective To test the effect of Banxia Xiexin Decoction(半夏泻心汤,BXD)on the contraction and relaxation of gastric smooth muscle(SM)in diabetic gastroparesis(DGP)model rats,and to explore the mechanism of BXD in the prevention and treatment of DGP through experiments of signal pathway both in vivo and in vitro.Methods Sixty Sprague-Dawley rats were divided into 6 groups according to a random number table:control group,model group,high-,medium-and low-dose BXD groups(9.2,4.6 and 1.8 g/(kg·d),respectively),and domperidone group(10 mg/(kg·d)),10 rats per group.DGP model was established initially by a single intraperitoneal injection of streptozotocin(STZ),and was confirmed by recording gastric emptying,intestinal transport velocity and gastric myoelectric activity of rats after 2 months.Each group was treated with a corresponding drug for 4 weeks.The mRNA and protein expressions of phospholipase C(PLC),inositol triphosphate(IP3),neuronal nitric oxide synthase(nNOS),and cyclic guanosine monophosphate(cGMP)dependent protein kinase G(PKG)were detected by reverse transcription-polymerase chain reaction and Western blot,respectively,while nitric oxide(NO)and cGMP expressions were detected by enzyme-linked immunosorbent assay.Gastric tissues were obtained from rats for primary cell culture preparation.Gastric SM cells were treated with 0.8µmol/L of STZ or STZ plus 1,000,500 and 200µg/mL of BXD or STZ plus 2.5µmol/mL of domperidone for 24,48,72 or 96 h,respectively.The length of gastric SM cells and intracellular Ca^2+concentration([Ca^2+]i)before and after BXD treatment was measured.Results Compared with the model group,high-and medium-dose BXD and domperidone significantly increased the expressions of PLC,IP3,NO,nNOS,cGMP and PKG in rat’s gastric tissue(P<0.01).Gastric SM cells treated with BXD showed a time-and dose-dependent increase in cell viability(P<0.01).The treatment with high-and medium-dose BXD and domperidone inhibited the increase in gastric SM cells length and increased[Ca^2+]i compared with the model cells(P<0.01).Conclusions Treatment with high-and medium-dose BXD significantly attenuated STZ-induced experimental DGP in rats.The therapeutic effect of BXD on DGP rats might be associated with the PLC-IP3-Ca^2+/NO-cGMP-PKG signal pathway.