Maria Giovanna Elia

Angiotensin II activates extracellular signal regulated kinases via protein kinase C and epidermal growth factor receptor in breast cancer cells.

Angiotensin II (Ang II) induces, through AT1, intracellular Ca2+ increase in both normal and cancerous breast cells in primary culture (Greco et al., 2002 Cell Calcium 2:1–10). We here show that Ang II stimulated, in a dose‐dependent manner, the 24 h‐proliferation of breast cancer cells in primary culture, induced translocation of protein kinase C (PKC)‐α, ‐β1/2, and δ (but not ‐ε, ‐η, ‐θ, ‐ζ, and ‐ι), and phosphorylated extracellular‐regulated kinases 1 and 2 (ERK1/2). The proliferative effects of Ang II were blocked by the AT1 antagonist, losartan. Also epidermal growth factor (EGF) had mitogenic effects on serum‐starved breast cancer cells since induced cell proliferation after 24 h and phosphorylation of ERK1/2. The Ang II‐induced proliferation of breast cancer cells was reduced by (a) Gö6976, an inhibitor of conventional PKC‐α and ‐β1, (b) AG1478, an inhibitor of the tyrosine kinase of the EGF receptor (EGFR), and (c) downregulation of 1,2‐diacylglycerol‐sensitive PKCs achieved by phorbol 12‐myristate 13‐acetate (PMA). A complete inhibition of the Ang II‐induced cell proliferation was achieved using the inhibitor of the mitogen activated protein kinase kinase (MAPKK or MEK), PD098059, or using Gö6976 together with AG1478. These results indicate that in human primary cultured breast cancer cells AT1 regulates mitogenic signaling pathways by two simultaneous mechanisms, one involving conventional PKCs and the other EGFR transactivation. J. Cell. Physiol. 196: 370–377, 2003.

PKC-ζ is required for angiotensin II-induced activation of ERK and synthesis of C-FOS in MCF-7 cells

We examined the signalling pathways responsible for the Ang II induction of growth in MCF‐7 human breast cancer cells. Ang II in MCF‐7 cells induced: (a) the translocation from the cytosol to membrane and nucleus of atypical protein kinase C‐ζ (PKC‐ζ) but not of PKC‐α, ‐δ, ‐ε and ‐η; (b) the expression of c‐fos mRNA and protein; (c) the phosphorylation of the extracellular signal‐regulated protein kinases 1 and 2 (ERK1/2). All these effects were due to the activation of the Ang II type I receptor (AT1) since they were blocked by the AT1 antagonist losartan. The Ang II‐stimulated ERK1/2 phosphorylation was blocked by (a) high doses of staurosporine, inhibitor of PKC‐ζ, and by a synthetic myristoylated peptide with sequences based on the endogenous PKC‐ζ pseudosubstrate region (ζ‐PS); (b) PD098059, a mitogen‐activated protein kinase kinase inhibitor (MAPKK/MEK); and, moreover, (c) the inhibitors of phosphoinositide 3‐kinases (PI3K), LY294002 and wortmannin, thus indicating that PI3K may act upstream of ERK1/2. The Ang II‐evoked c‐fos induction was blocked only by high doses of staurosporine and by ζ‐PS whilst PD098059, LY294002 and wortmannin were ineffective, thus indicating that c‐fos induction is not due to ERK1/2 activity. When the epidermal growth factor‐receptor (EGFR) tyrosine kinase activity was inhibited by the use of its inhibitor AG1478, Ang II was still able to induce ERK1/2 phosphorylation and c‐fos expression, therefore proving that the transactivation of EGFR was not required for these Ang II effects in MCF‐7 cells. The previously reported proliferation of MCF‐7 cells induced by Ang II was blocked by PD098059 and by wortmannin in a dose‐dependent manner, thereby indicating that in MCF‐7 cells the PI3K and ERK pathways mediate the mitogenic signalling of AT1. Our results suggest that in MCF‐7 cells Ang II activates multiple signalling pathways involving PKC‐ζ, PI3K and MAPK; of these pathways only PKC‐ζ appears responsible for the induction of c‐fos. J. Cell. Physiol. 197: 61–68, 2003© 2003 Wiley‐Liss, Inc.

Mitogenic signalling by B2 bradykinin receptor in epithelial breast cells

The kinin peptides are released during inflammation and are amongst the most potent known mediators of vasodilatation, pain, and oedema. A role in the modulation or induction of healthy breast tissue growth has been postulated for tissue kallikrein present in human milk. Moreover, tissue kallikrein was found in malignant human breast tissue and bradykinin (BK) stimulates the proliferation of immortalised breast cancer cells. Aim of the present article was to investigate whether BK also exerts mitogenic activity in normal breast epithelial cells and partially characterise the signalling machinery involved. Results show that BK increased up to 2‐fold the 24 h proliferation of breast epithelial cells in primary culture, and that the BK B2 receptor (not B1) inhibitor alone fully blocked the BK response. Intracellular effects of B2 stimulation were the following: (a) the increase of free intracellular Ca2+ concentration by a mechanism dependent upon the phospholipase C (PLC) activity; (b) the cytosol‐to‐membrane translocation of conventional (PKC)‐α and ‐β isozymes, novel PKC‐δ, ‐ε, and ‐η isozymes; (c) the phosphorylation of the extracellular‐regulated kinase 1 and 2 (ERK1/2); and (d) the stimulation of the expression of c‐Fos protein. EGF, a well known stimulator of cell proliferation, regulated the proliferative response in human epithelial breast cells to the same extent of BK. The effects of BK on proliferation, ERK1/2 phosphorylation, and c‐Fos expression were abolished by GF109203X, which inhibits PKC‐δ isozyme. Conversely, Gö6976, an inhibitor of PKC‐α and ‐β isozymes, and the 18‐h treatment of cells with PMA, that led to the complete down‐regulation of PKC‐α, ‐β, ‐ε, and ‐η, but not of PKC‐δ, did not have any effect, thereby indicating that the PKC‐δ mediates the mitogenic signalling of BK. Phosphoinositide 3‐kinase (PI3K), tyrosine kinase of the epidermal growth factor receptor (EGFR), and mitogen activated protein kinase kinases (MEK) inhibitors were also tested. The results suggest that EGFR, PI3K, and ERK are required for the proliferative effects of BK. In addition, the BK induced cytosol‐to‐membrane translocation of PKC‐δ was blocked by PI3K inhibition, suggesting that PI3K is upstream to PKC‐δ. In conclusion, BK has mitogenic actions in cultured human epithelial breast cells; the activation of PKC‐δ through B2 receptor acts in concert with ERK and PI3K pathways to induce cell proliferation. J. Cell. Physiol. 201: 84–96, 2004.

Activation of P2Y2 receptor induces c-FOS protein through a pathway involving mitogen-activated protein kinases and phosphoinositide 3-kinases in HeLa cells.

The effects of P2Y2 purinoceptor activation on c‐Fos expression and the signaling pathways evoked by extracellular ATP/UTP in HeLa cells were investigated. We found that P2Y2 activation induced c‐Fos protein and phosphorylated the extracellular signal‐regulated kinases 1 and 2 (ERK1/2). The P2Y2‐stimulated c‐Fos induction was partly blocked (a) by U73122, a phospholipase C inhibitor, (b) by Gö6976, a conventional PKC inhibitor, (c) by PD098059, a mitogen‐activated protein kinase kinase inhibitor, and, moreover, (d) by the inhibitors of phosphoinositide 3‐kinases (PI3K), LY294002 and wortmannin. When Gö6976 and PD098059, or Gö6976 and wortmannin, were combined there was a totally inhibition of P2Y2‐induced c‐Fos increase. Either U73122 or Gö6976 did not inhibit ERK1/2 phosphorylation induced by ATP/UTP, while it was inhibited by LY294002 (or wortmannin) and by staurosporine. Additionally, wortmannin inhibited the cytosol‐to‐membrane translocation of PKC‐ε induced by ATP/UTP. These data indicated that agonist‐induced PI3K and downstream PKC‐ε activation mediated the effect of ATP/UTP on ERK1/2 activation. To test the biological consequences of ERK1/2 activation, the effect of P2Y2 on cell functions were examined. P2Y2 stimulation increased cell proliferation and this effect was attenuated by PD098059 in a dose‐dependent manner, thereby indicating that the ERK pathway mediates mitogenic signaling by P2Y2. In conclusion, the activation of conventional PKCs through P2Y2 receptor acts in concert with ERK and PI3K/PKC‐ε pathways to induce c‐Fos protein and HeLa cell proliferation.

Differential signalling of purinoceptors in HeLa cells through the extracellular signal-regulated kinase and protein kinase C pathways

We have previously shown that HeLa cells express P2Y2 and P2Y6 receptors endogenously and determined the pathways by which the P2Y2 controls proliferation and Na+/K+ATPase activity. Our objective in this study was to investigate the hypothesis that P2Y6 also controls proliferation and Na+/K+ATPase activity; the pathways used in these actions were partially characterised. We found that P2Y6 activation controlled cell proliferation but not the activity of the Na+/K+ATPase. UDP activation of P2Y6 provoked: (a) an increase in free cytosolic calcium; (b) the activation of protein kinase C‐α, ‐β, ‐δ, ‐ε, and ‐ζ but not of PKC‐ι and ‐η; (c) the phosphorylation of the extracellular signal‐regulated protein kinases 1 and 2 (ERK1/2); (d) the expression of c‐Fos protein. The P2Y6‐induced cell proliferation was blocked by the mitogen‐activated protein kinase kinase (MAPKK) inhibitor PD098059, thereby indicating that the ERK pathway mediates the mitogenic signalling of P2Y6. PKC and phosphoinositide 3‐kinase (PI3K) inhibitors were tested at two different time points of ERK1/2 phosphorylation (10 and 60 min). The results suggest that novel PKCs and PI3K initiate the response but both conventional and atypical PKCs are required for the maintenance of the UDP‐induced phosphorylation of ERK1/2. The induction of c‐Fos was greatly diminished by conventional or atypical PKC‐ζ inhibition, suggesting that it may be due to PKC‐α/β and ‐ζ activity. These observations demonstrate that UDP acts as a proliferative agent in HeLa cells activating multiple signalling pathways involving conventional, novel, and atypical PKCs, PI3K, and ERK. Of these pathways, conventional and atypical PKCs appear responsible for the induction of c‐Fos, while ERK is responsible for cell proliferation and depends upon both novel and atypical PKCs and PI3K activities.

AT1 angiotensin II receptor mediates intracellular calcium mobilization in normal and cancerous breast cells in primary culture

Angiotensin II (Ang II) increases intracellular calcium concentration ([Ca2+]i) in both normal and cancerous human breast cells in primary culture. Maximal [Ca2+]i increase is obtained using 100nM Ang II in both cell types; in cancerous breast cells, [Ca2+]i increase (delta[Ca2+]i) is 135+/-10nM, while in normal breast cells it reaches 65+/-5 nM (P<0.0001). In both cell types, Ang II evokes a Ca2+ transient peak mediated by thapsigargin (TG) sensitive stores; neither Ca2+ entry through L-type membrane channels or capacitative Ca2+ entry are involved. Type I Ang II receptor subtype (AT1) mediates Ang II-dependent [Ca2+]i increase, since losartan, an AT1 inhibitor, blunted [Ca2+]i increase induced by Ang II in a dose-dependent manner, while CGP 4221A, an AT2 inhibitor, does not. Phospholipase C (PLC) is involved in this signaling mechanism, as U73122, a PLC inhibitor, decreases Ang II-dependent [Ca2+]i transient peak in a dose-dependent mode.Thus, the present study provides new information about Ca2+ signaling pathways mediated through AT1 in breast cells in which no data were yet available.

Increase of [Ca2+]i via activation of ATP receptors in PC-Cl3 rat thyroid cell line

In PC-Cl3 rat thyroid cell line, ATP and UTP provoked a transient increase in [Ca(2+)](i), followed by a lower sustained phase. Removal of extracellular Ca(2+) reduced the initial transient response and completely abolished the plateau phase. Thapsigargin (TG) caused a rapid rise in [Ca(2+)](i) and subsequent addition of ATP was without effect. The transitory activation of [Ca(2+)](i) was dose-dependently attenuated in cells pretreated with the specific inhibitor of phospholipase C (PLC), U73122. These data suggest that the ATP-stimulated increment of [Ca(2+)](i) required InsP(3) formation and binding to its specific receptors in Ca(2+) stores. Desensitisation was demonstrated with respect to the calcium response to ATP and UTP in Fura 2-loaded cells. Further studies were performed to investigate whether the effect of ATP on Ca(2+) entry into PC-Cl3 cells was via L-type voltage-dependent Ca(2+) channels (L-VDCC) and/or by the capacitative pathway. Nifedipine decreased ATP-induced increase on [Ca(2+)](i). Addition of 2 mM Ca(2+) induced a [Ca(2+)](i) rise after pretreatment of the cells with TG or with 100 microM ATP in Ca(2+)-free medium. These data indicate that Ca(2+) entry into PC-Cl3 stimulated with ATP occurs through both an L-VDCC and through a capacitative pathway. Using buffers with differing Na(+) concentrations, we found that the effects of ATP were dependent of extracellular Na(+), suggesting that a Na(+)/Ca(2+) exchange mechanism is also operative. These data suggest the existence, in PC-Cl3 cell line, of a P2Y purinergic receptor able to increase the [Ca(2+)](i) via PLC activation, Ca(2+) store depletion, capacitative Ca(2+) entry and L-VDCC activation.

Activation of P2Y2 purinoceptor inhibits the activity of the Na+/K+-ATPase in HeLa cells

The role of ATP on regulation of the Na(+)/K(+)-ATPase activity in the human cancerous HeLa cells was investigated. HeLa cells stimulated with increasing ATP concentrations showed a dose-dependent inhibition of the Na(+)/K(+)-ATPase activity. These effects were also obtained by UTP. ATP and UTP provoked a rise in intracellular calcium concentration ([Ca(2+)](i)) persisting for at least 4 min. The inhibitor of phospholipase C, U73122, blocked the elevation of [Ca(2+)](i) provoked by ATP/UTP. The expression of mRNA for P2Y2 and P2Y6 receptors was demonstrated by RT-PCR. ATP/UTP activated PKC-alpha, -betaI and -epsilon isoforms, but not PKC-delta and -zeta. The inhibition of the Na(+)/K(+)-ATPase activity by ATP/UTP was blocked by Gö6976, a specific inhibitor of the calcium-dependent PKCs. In conclusion, our results suggest that ATP/UTP modulate Na(+)/K(+)-ATPase activity in HeLa cells through the P2Y2 purinoceptor via calcium mobilisation and activation of calcium-dependent PKCs.

Disturbances in purinergic [Ca2+]i signaling pathways in a transformed rat thyroid cell line

It was previously shown that in rat thyroid PC-Cl3 cell line, a purinergic P2Y receptor increases the concentration of free cytosolic Ca(2+) ([Ca(2+)](i)) via phospholipase C activation. We here studied whether in a transformed cell line (PC-E1Araf) derived from parental PC-Cl3 cells, ATP is still able to transduce the [Ca(2+)](i)-based intracellular signal.We demonstrate the expression of mRNA for P2Y2 in both PC-Cl3 and PC-E1Araf cells; mRNAs for P2Y1, P2Y4, P2Y6 and P2Y11 were absent. In both cell lines activation of P2Y2 receptor provokes a transient increase in [Ca(2+)](i) followed by a lower sustained phase persisting for over 5min in PC-Cl3 and only 1.5 min in PC-E1Araf cells. In both cell lines the [Ca(2+)](i) reached a plateau level significantly higher than the basal [Ca(2+)](i) level persisting for over 10 min. Removal of extracellular Ca(2+) reduced the initial transient response to ATP in PC-Cl3, but not in PC-E1Araf cells, and completely abolished the plateau phase in both cell lines. In the presence of extracellular Ca(2+) thapsigargin (TG) caused a rise in [Ca(2+)](i) significantly higher in PC-Cl3 than transformed PC-E1Araf cells, while in Ca(2+)-free medium the effect of TG was similar in both cell lines. The capacitative Ca(2+)-entry in PC-Cl3 resulted significantly higher than in PC-E1Araf cells. Further studies were performed in order to investigate whether the different effects of ATP on [Ca(2+)](i) was due to variation in divalent cation plasma membrane permeability. PC-E1Araf cells showed a much lower permeability to Ca(2+), Ba(2+), Sr(2+), Mn(2+), and Co(2+) that may be responsible for the differences in purinergic Ca(2+) signaling pathway with respect to parental PC-Cl3 cells.