Fasting-mimicking diet blocks triple-negative breast cancer and cancer stem cell escape

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Prostaglandin E2-protein kinase a signaling and protein phosphatases-1 and -2A regulate human head and neck squamous cell carcinoma motility, adherence, and cytoskeletal organization

Human head and neck squamous cell carcinoma (HNSCC) cultures were established from cancers of two patients. These cells were used to study if phosphorylation reactions by protein kinase A (PKA) and dephosphorylation reactions by protein phosphatases-1 and -2A (PP-1/2A) regulate tumor motility and adhesion to extracellular matrix components, and if this might be associated with cytoskeletal reorganization. Both cultures were motile and adherent to collagen I, fibronectin, vitronectin and laminin. Motility and adhesiveness was dependent on production of prostaglandin E₂ PGE₂ and on PKA activation. Blocking PP-1/2A activity with okadaic acid resulted in a PKA-dependent increase in m otility and, in some instances, adhesiveness by the HNSCC cells. The okadaic acid-induced increase in motility and adhesiveness coincided with a reduction in filamentous actin. These data suggest PKA and PP-1/2A have opposing effects in regulating the motility, adherence, and actin polymerization.     

The thermogenic activity of adjacent adipocytes fuels the progression of ccRCC and compromises anti-tumor therapeutic efficacy

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Effects of different kinases and phosphatases on nuclear and cytoplasmic maturation of bovine oocytes

Phosphorylation is considered as a common post-translational modification implicated in the control of various key enzymes. In somatic and germinal cells, important regulators of the cell cycle are controlled by their phosphorylation status, and some act as kinases or phosphatases themselves. Bovine oocytes are blocked in the germinal vesicle (GV) stage until either an LH surge occurs or until oocytes are released from the inhibitory influence of the follicle. Meiotic resumption in vitro is therefore an excellent model for the study of phosphorylation events that occur in the G2/M transition, a control point of the cellular cycle. To better understand this transition, we have modulated, either directly or indirectly, kinases using known effectors (epidermal growth factor, EGF; isobutyl-methylxanthine-forskolin, Bx-Fk; 6-dimethylaminopurine, 6-DMAP) or phosphatases (okadaic acid, OA) or cycloheximide, which is known to inhibit maturation through protein synthesis suppression. With this procedure, influence on meiotic resumption and phosphoprotein patterns was verified. Both EGF and OA accelerated nuclear maturation after 9 hr of culture. Only 23% (n = 140) and 9% (n = 111) of oocytes were still at GV stage with EGF and OA, respectively, compared to 41% (n = 105) of control oocytes. The different treatments changed the protein patterns in oocytes. In cumulus cells, the patterns were especially modified by the OA treatment. Characteristic changes that occur in germ cells were also identified. Nuclear maturation was inhibited by modulators of kinase (6-DMAP, GV = 74%, n = 126; cAMP dependent protein kinase (PKA) stimulators, Bx-Fk, GV = 71%, n = 129) likewise, phosphoprotein patterns were affected, especially in oocytes. The cycloheximide treatment was able to maintain nearly all oocytes in GV after 9 hr of culture (GV = 92%, n = 131). This analysis allowed the identification of substrates for the different effectors used in this study and also helped in determining the levels of phosphorylation required for nuclear maturation. © 1995 wiley-Liss, Inc.     

N-Acetyl-d-Glucosamine Induces Germination in Candida albicans through a Mechanism Sensitive to Inhibitors of cAMP-Dependent Protein Kinase

The present study examines the involvement of cAMP-dependent protein kinase (PKA) in the dimorphic transition of Candida albicans by assessing the in vivo effect of two permeable PKA inhibitors on N-acetyl-d-glucosamine (GlcNAc)- and serum-induced differentiation. The permeable myristoylated derivative of the heat-stable PKA inhibitor (MyrPKI), which inhibited C. albicans PKA in vitro, caused a concentration-dependent inhibition of germ-tube formation in cultures induced to germinate by GlcNAc; germination halted irrespective of the time of addition of the inhibitor. MyrPKI also blocked dibutyryl-cAMP (dbcAMP)- and glucagon-stimulated germination but did not affect serum-induced germination. H-89, another highly specific PKA inhibitor, displayed the same effect on germination. Neither MyrPKI nor H-89 had any effect on budding of yeast cells. In conclusion, our results indicate that cAMP-mediated activation of PKA plays a pivotal role in the biochemical mechanism underlying morphogenesis.     

Effect of essential fatty acid deficiency on G-proteins, cAMP-dependent protein kinase activity and mucin secretion in the rat submandibular salivary glands

Studies were conducted to determine whether β-adrenergic cell signalling is altered in submandibular salivary glands (SMSG) is essential fatty acid (EFA) deficiency. Three groups of rats were fed diets which were deficient in EFA (EFAD), marginally deficient in EFA (MEFAD) or contained sufficient amount of EFA (Control). Rats were killed after 20 wk on diets, SMSG were dissected out and cyclic AMP-dependent protein kinase (PKA) activity was measured. The specific enzyme activities were higher in the homogenates and supernatant fractions of the gland from EFAD and MEFAD rats compared with the controls. The relative levels of guanine nucleotide-binding regulatory proteins (Gs and Gi) were also measured in the SMSG membranes of rats fed the 3 diets. The levels of Gs were significantly higher in the EFAD and MEFAD groups than in the controls. No significant differences were observed in the secretion of trichloroacetic acid-phosphotungstic acid (TCA-PTA) precipitable glycoproteins from the SMSG slices among the 3 dietary groups.