Type II cyclic guanosine monophosphate-dependent protein kinase inhibits Rac1 activation in gastric cancer cells

Abstract

Abstract. Enhanced motility of cancer cells is a critical step in promoting tumor metastasis, which remains the major cause of gastric cancer-associated mortality. The small GTPase Rac1 is a key signaling component in the regulation of cell migration. Previous studies have demonstrated that Rac1 activity may be regulated by protein kinase G (PKG); however, the underlying mechanism is not yet clear. The current study aimed to investigate the effect of type II cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG II) on Rac1 activity. The human gastric cancer cell line AGS was infected with adenoviral constructs encoding PKG II to increase the expression of this enzyme, and treated with a cGMP analog (8-pCPT-cGMP) to induce its activation. A Transwell assay was employed to measure cell migration, and the activity of Rac1 was assessed using a pull-down assay. Immunoprecipitation was used to isolate the Rac1 protein. Phosphorylation of phosphatidylinositol 4,5 bisphosphate 3 kinase (PI3K) and its downstream effecter protein kinase B (Akt) are associated with lysophosphatidic acid (LPA)-induced motility/migration of cancer cells. Extracellular signal regulated kinase (ERK) is the major signaling molecule of the Mitogen activated protein kinase (MAPK) mediated signaling pathway. ERK and its upstream activator MAPK kinase (MEK) are also involved in LPA-induced motility/migration of cancer cells. Phosphorylation of PI3K/Akt, MEK/ERK and enriched Rac1 were detected by western blotting. The results revealed that blocking the activation of Rac1 by ectopically expressing an inactive Rac1 mutant (T17N) impeded LPA-induced cell migration. Increased PKG II activity inhibited LPA-induced migration and LPA-induced activation of Rac1; however, it had no effect on the phosphorylation of Rac1. PKG II also inhibited the activation of PI3K/Akt and MEK/ERK mediated signaling, which is important for LPA-induced Rac1 activation. These results suggest that PKG II affects LPA-stimulated migration of AGS cells by blocking Rac1 activation, via inhibition of PI3K/Akt and MEK/ERK mediated signaling.

Quantitative Analysis of Proteome in Non-functional Pituitary Adenomas: Clinical Relevance and Potential Benefits for the Patients

“…It has been reported that cGMP promoted tumorigenesis and anticancer effects. For example, the activated cGMP/PKG pathway induced multiple cancers (33,(35)(36)(37). Studies found specifically activated protein kinase G1 (PKG1) triggered MAPK signaling pathway to promote growth of melanoma (38).…”

High expression of Nectin-4 is associated with unfavorable prognosis in gastric cancer

“…125, may help to make a distinction between benign gynecological diseases and ovarian cancer (19). Rac1 signaling is involved in in tumor growth and progression of numerous types of cancer, and a number of functions in the progression of cancer, including proliferation, differentiation, migration, invasion, survival and cancer metastasis (28)(29)(30). Rac1 signaling is necessary for the extension of protrusions, including the formation of lamellipodia, which is crucial for cell-cell adherence (31,32).…”

PKG II inhibits PDGF‐BB triggered biological activities by phosphorylating PDGFRβ in gastric cancer cells

“…Serial reports have demonstrated that PKG II inhibited EGF‐EGFR related MAPK/JNK, MAPK/ERK, and PI3K/AKT mediated signal transduction pathways, resulting from the impediment of EGFR activation in gastric cancer cell lines (Lan et al, ; Wu et al, ; Jiang et al, ; Wu et al, ). In addition, PKG II also effectively inhibited the phosphorylation/activation of other RTK, such as vascular endothelial growth factor receptor (VEGFR) and c‐Met (Wang et al, ; Wu et al, ). Because of the high conservation of RTKs in molecular structure, we speculated that PKG II may also have a similar inhibitory effect on platelet‐derived growth factor receptor (PDGFR).…”