Expression and functional characterization of a pHis-tagged human bradykinin B2 receptor in COS-7 cells

A polyHis-tagged bradykinin (BK) B2 receptor (pHis-BKR) cDNA was constructed and expressed in COS-7 cells. The pHis-BKR is suitable for both immunoprecipitation and immunoblotting with anti-polyHis antibodies and can be easily purified using Ni-NTA columns. Immunochemical detection revealed a molecular mass of approximately 66 kDa. The pHis-BKR is capable of mediating BK-induced stimulation of inositol phosphate formation as well as of mitogen-activated protein kinase (MAPK) activity. Compared with the wild-type receptor (WT-BKR) the tagged receptor showed a slightly enhanced affinity towards BK but a reduced expression level. Despite these modified pharmacological properties the pHis-tagged BKR may be a useful tool for studying BKR modifications and signaling.

Bradykinin B(2) receptor-mediated mitogen-activated protein kinase activation in COS-7 cells requires dual signaling via both protein kinase C pathway and epidermal growth factor receptor transactivation

The signaling routes linking G-protein-coupled receptors to mitogen-activated protein kinase (MAPK) may involve tyrosine kinases, phosphoinositide 3-kinase gamma (PI3Kgamma), and protein kinase C (PKC). To characterize the mitogenic pathway of bradykinin (BK), COS-7 cells were transiently cotransfected with the human bradykinin B(2) receptor and hemagglutinin-tagged MAPK. We demonstrate that BK-induced activation of MAPK is mediated via the alpha subunits of a G(q/11) protein. Both activation of Raf-1 and activation of MAPK in response to BK were blocked by inhibitors of PKC as well as of the epidermal growth factor (EGF) receptor. Furthermore, in PKC-depleted COS-7 cells, the effect of BK on MAPK was clearly reduced. Inhibition of PI3-Kgamma or Src kinase failed to diminish MAPK activation by BK. BK-induced translocation and overexpression of PKC isoforms as well as coexpression of inactive or constitutively active mutants of different PKC isozymes provided evidence for a role of the diacylglycerol-sensitive PKCs alpha and epsilon in BK signaling toward MAPK. In addition to PKC activation, BK also induced tyrosine phosphorylation of EGF receptor (transactivation) in COS-7 cells. Inhibition of PKC did not alter BK-induced transactivation, and blockade of EGF receptor did not affect BK-stimulated phosphatidylinositol turnover or BK-induced PKC translocation, suggesting that PKC acts neither upstream nor downstream of the EGF receptor. Comparison of the kinetics of PKC activation and EGF receptor transactivation in response to BK also suggests simultaneous rather than consecutive signaling. We conclude that in COS-7 cells, BK activates MAPK via a permanent dual signaling pathway involving the independent activation of the PKC isoforms alpha and epsilon and transactivation of the EGF receptor. The two branches of this pathway may converge at the level of the Ras-Raf complex.

[Diagnostic and therapeutic concepts of HPV infection in HIV-positive women]

Among HIV-seropositive women there is a high prevalence of anogenital human papillomavirus (HPV) infection. HPV-DNA is more frequent detected in cervicovaginal-lavage specimens from HIV-seropositive women as in those from HIV-seronegative women. We and others suggest that HIV-infection increases the risk to have HPV-associated lesions of the lower female genital tract, especially the risk for developing a squamous intraepithelial lesion of the cervix. In this report we describe the current diagnostic and therapeutic strategies in HIV-seropositive women with HPV-infection. The gynecological examination should be performed at six to twelve month intervals, including the colposcopy and the Pap smear test. We hope to improve the quality of our screening program by doing an additional HPV-test. At last we investigate the CD4+ T-lymphocyte counts because it is observed that women with low CD4+ cell counts (< 200/microliter) were more likely to have persistent HPV-infection as those with higher counts (> 500/microliter). The treatment method is dependent on the development of the HPV-associated lesion and the clinical status of the HIV infected women. In cases with external warts local application of Condylox should be the first line treatment. Probably in about few months we could use other drugs like Wartec or Aldara in Germany. But the effectiveness of these drugs in HIV-positive women has to be proven yet. In the cause of persistence of external warts or recurrence of the disease the systemical application of Intron A or Roferon A is possible. The CO2-lasertreatment is performed under colposcopic guidance, especially in cases with multicentric condylomatous lesions. The treatment of cervical intraepithelial neoplasia (CIN) by CO2-laservaporisation or Loop Electrosurgical Excision Procedure (LEEP) is based on the clear colposcopic visualisation of the upper limit of the lesion. If CIN reaches the endocervix, being out of colposcopic view, and the squamocolumnar junction is localised in the endocervical canal conisation by laser or cold knife has to be performed. Before performing the treatment of CIN one should exclude multicentric cervical, vaginal and vulval intraepithelial neoplasia by colposcopy, because multicentric intraepithelial neoplasia of the lower female genital tract is more frequently than in HIV-seronegative women. Multicentric disease seems to be one cause of the high recurrence of HIV-seropositive women. However, higher levels of immunosuppression (CD4+ T-lymphocyte counts < 200/microliter) are also important determinants of recurrence of the disease. Therefore, an accurate short-term follow-up with colposcopy, Pap test and HPV test should be carried out after the treatment of HIV-seropositive women with low CD4+ counts.

A novel mitogenic signaling pathway of bradykinin in the human colon carcinoma cell line SW-480 involves sequential activation of a Gq/11 protein, phosphatidylinositol 3-kinase beta, and protein kinase Cepsilon

The signaling routes connecting G protein-coupled receptors to the mitogen-activated protein kinase (MAPK) pathway reveal a high degree of complexity and cell specificity. In the human colon carcinoma cell line SW-480, we detected a mitogenic effect of bradykinin (BK) that is mediated via a pertussis toxin-insensitive G protein of the Gq/11 family and that involves activation of MAPK. Both BK-induced stimulation of DNA synthesis and activation of MAPK in response to BK were abolished by two different inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and LY 294002, as well as by two different inhibitors of protein kinase C (PKC), bisindolylmaleimide and Ro 31-8220. Stimulation of SW-480 cells by BK led to increased formation of PI3K lipid products (phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3, 4-bisphosphate) and to enhanced translocation of the PKCepsilon isoform from the cytosol to the membrane. Both effects of BK were inhibited by wortmannin, too. Using subtype-specific antibodies, only the PI3K subunits p110beta and p85, but not p110alpha and p110gamma, were detected in SW-480 cells. Finally, p110beta was found to be co-immunoprecipitated with PKCepsilon. Our data suggest that in SW-480 cells, (i) dimeric PI3Kbeta is activated via a Gq/11 protein; (ii) PKCepsilon is a downstream target of PI3Kbeta mediating the mitogenic signal to the MAPK pathway; and (iii) PKCepsilon associates with the p110 subunit of PI3Kbeta. Thus, these results add a novel possibility to the emerging picture of multiple pathways linking G protein-coupled receptors to MAPK.

[Studies with high-dose chemotherapy and subsequent autologous stem cell transplantation in breast carcinoma]

Survival rates for several subgroups of patients with breast cancer treated with conventional therapy remain poor. Only about 30% of patients with primary breast cancer involving more than 9 axillary lymph nodes remain disease-free at 5 years from diagnosis despite surgery, conventional-dose chemotherapy and radiotherapy. Metastatic breast cancer with 5 year survival rates of about 3% generally represents incurable disease. Chemotherapeutic agents are conventionally limited by side effects. The easy procurement of haematopoietic stem cell support through mobilization of peripheral blood progenitors has spurred the development of new strategies employing high-dose treatment for treatment of high risk breast cancer. Autologous stem cell support antagonizes chemotherapy-induced myelotoxicity and thereby allows dose escalation by a factor of 1.5 to about 20. Pilot studies evaluating significant dose escalation in adjuvant treatment of patients with advanced disease have resulted in an apparent improvement in event-free survival rates to over 70%. Repetitive applications of chemotherapy at myeloablative doses are now increasingly being used. Data from prospectively randomized phase III trials will not be available before the end of 1998. For metastatic breast cancer one prospective, randomized clinical trial has been published. Results are significantly better for patients who have been treated by high-dose chemotherapy compared to patients who received conventional polychemotherapy (median survival 90 vs. 45 weeks). For methodological reasons (small patient numbers, patient selection, weak standard therapy etc.) results from the trials cited above are under discussion. Until publication of further results from ongoing phase III trials HDC for breast cancer remains experimental and should not be given outside of clinical trials.

Novel bradykinin signalling events in PC-12 cells: stimulation of the cAMP pathway leads to cAMP-mediated translocation of protein kinase Cepsilon

In the rat pheochromocytoma cell line PC-12, bradykinin (BK) stimulated phosphatidylinositol hydrolysis by 4-5-fold and, additionally, intracellular cAMP accumulation by approx. 1.6-fold. EC50 values for BK were 3 nM and 2 nM respectively. The BK-induced increase in cAMP accumulation was paralleled by a 1.6-fold increase in protein kinase A (PKA) activity. The time course of BK-stimulated inositol phosphate formation was rapid (t1/2<1 min), whereas the BK-induced cAMP accumulation was lagging (t1/2 approx. 6 min). The effect of BK on the cAMP pathway was independent of pertussis toxin, excluding an indirect stimulation of adenylate cyclase via betagamma-complexes from Gi or Go proteins. Two different protein kinase C (PKC) inhibitors, bisindolylmaleimide and Ro 31-820, failed to prevent BK-induced cAMP accumulation, and exclude PKC as mediator of BK action on adenylate cyclase. In contrast, the stimulatory effect of BK on cAMP accumulation was completely abolished by two calmodulin antagonists, chlorpromazine and ophiobolin, suggesting an indirect, Ca2+/calmodulin-mediated effect of BK on the cAMP pathway. In addition, exposure of PC-12 cells to BK resulted in a translocation of the PKC isoforms alpha, delta, epsilon and zeta displaying different kinetics. The BK-induced translocations of the PCDs alpha and delta were rapid and biphasic, whereas the PKCs epsilon and zeta revealed a slower and slightly transient translocation in response to BK. The BK-elicited translocation of PKCepsilon, but not that of the PKCs alpha, delta and zeta, was prevented by two different inhibitors of adenylate cyclase, 2',5'-dideoxyadenosine and MDL-12,330A, as well as the PKA inhibitor adenosine 3':5'-monophosphothioate. These findings suggest that the BK-induced translocation of novel (n)PKCepsilon is mediated via the cAMP pathway. Since nPKCepsilon appears to regulate neurite outgrowth in PC-12 cells [Hundke, McMahon, Dadgar and Messing (1995) J. Biol. Chem. 270, 30134-30140] our results provide evidence for a novel signalling mechanism that might be involved in BK-induced neuronal differentiation of PC-12 cels.

[Significance of stem cell-supported high-dose chemotherapy in the treatment of gynecological malignancies: indications and current clinical trials in the Federal Republic of Germany]

The use of hematopoetic growth factors and stem cell support reduces the dose limiting hematopoetic toxicity's, resulting in a remarkable increase in dose intensity of chemotherapy. As far as data from phase I/II trials are available high dose chemotherapy (HDC) may be integrated in the systemic treatment of breast and ovarian cancers. In metastatic breast cancer HDC may induce fairly high but short response rates. Long term survival is expected in 20% of the cases. Patients with limited metastatic disease, without significant prior chemotherapy, partial or complete response to induction chemotherapy and complete remission after HDC may benefit from HDC. In phase I/II trials HDC improved recurrence free survival in high risk patients (e.g. > 9 positive LN) compared to historic controls and may therefore be a curative approach. Ovarian cancer is very chemosensitive. Conventional chemotherapies induce multidrug resistance rapidly. Just as in breast cancer-Phase I/II trials demonstrated high response rates to HDC, which again were short of duration.

Signaling effects of alpha-thrombin and SFLLRN in rat glioma C6 cells

Effects of thrombin on brain cells, including change of neurite outgrowth and astrocyte shape, are described, but the molecular mechanisms are unclear. We investigated the effects of human alpha-thrombin and a six amino acid thrombin receptor activating peptide (TRAP-6, SFLLRN) on [Ca2+]i, phosphoinositide hydrolysis, and protein kinase C in rat glioma C6 cells. Stimulation of C6 cells with both alpha-thrombin and TRAP-6 resulted in [Ca2+]i mobilization, [3H]Inositol phosphate response, and enhanced immunoreactivity of the protein kinase C (PKC) isoenzymes alpha, beta, gamma, delta, and epsilon. Results suggest that alpha-thrombin and TRAP-6 activate at least partially the same intracellular signaling pathways in rat glioma C6 cells, which is evidence for involvement of "tethered ligand" receptor in thrombin induced signaling in glioma C6 cells.

Tyrosine phosphorylation of GSalpha and inhibition of bradykinin-induced activation of the cyclic AMP pathway in A431 cells by epidermal growth factor receptor

An increasing amount of experimental data suggest that cross-talk exists between pathways involving tyrosine kinases and heterotrimeric G proteins. In a previous study, we demonstrated that bradykinin (BK) increases the intracellular accumulation of cAMP in the human epidermoid carcinoma cell line A431 by stimulating adenylate cyclase activity via a stimulatory G protein (Gsalpha) (Liebmann, C., Graness, A., Ludwig, B., Adomeit, A., Boehmer, A., Boehmer, F.-D., Nürnberg, B., and Wetzker, R. (1996) Biochem. J. 313, 109-118). Here, we present several lines of evidence indicating the ability of epidermal growth factor (EGF) to suppress BK-induced activation of the cAMP pathway in A431 cells via tyrosine phosphorylation of Gsalpha. Gsalpha was specifically immunoprecipitated from A431 cells using the anti-alphas antiserum AS 348. Tyrosine phosphorylation of Gsalpha was detectable in EGF-pretreated cells with monoclonal anti-phosphotyrosine antibodies. Additionally, A431 cells were labeled with [32P]orthophosphate in vivo and treated with EGF, and the resolved immunoprecipitates were subjected to amino acid analysis. The results clearly indicate that EGF induces tyrosine phosphorylation of Gsalpha in A431 cells. Treatment of A431 cells with EGF decreased BK-induced cAMP accumulation in intact cells as well as the stimulation of adenylate cyclase by BK, NaF, and guanyl nucleotides, but not by forskolin. Also, EGF treatment abolished both the BK- and isoprenaline-induced stimulation of guanosine 5'-O-(3-[35S]thiotriphosphate) binding to Gsalpha. In contrast, the BK-evoked, Gq-mediated stimulation of inositol phosphate formation in A431 cells was not affected by EGF pretreatment. Thus, EGF-induced tyrosine phosphorylation of Gsalpha is accompanied by a loss of its susceptibility to G protein-coupled receptors and its ability to stimulate adenylate cyclase via guanyl nucleotide exchange. We propose that Gsalpha may represent a key regulatory protein in the cross-talk between the signal transduction pathways of BK and EGF in A431 cells.

Dual bradykinin B2 receptor signalling in A431 human epidermoid carcinoma cells: activation of protein kinase C is counteracted by a GS-mediated stimulation of the cyclic AMP pathway

Cell membranes of the human epidermoid cell line A431 express classical bradykinin (BK) B2 receptors, as assessed by [3H]BK binding studies. Furthermore, stimulation by BK induced a time-dependent modulation of protein kinase C (PKC) activity in A431 cells: a rapid activation (t1/2 approximately 1 min) is followed by a slow inhibition (t1/2 approximately 20 min) of PKC translocation measured by [3H]phorbol 12,13-dibutyrate binding. In addition, BK stimulated both adenylate cyclase activity in A431 membranes and accumulation of intracellular cyclic AMP (cAMP) in intact cells in a retarded manner. A possible BK-induced activation of the cAMP pathway mediated via PKC, phospholipase D, prostaglandins or Ca2+/calmodulin was excluded. A 35 kDa protein was found in A431 membranes to be specifically phosphorylated in the presence of both BK and protein kinase A (PKA). An anti-alpha s-antibody, AS 348, abolished stimulation of adenylate cyclase activity in response to BK, cholera toxin and isoprenaline, strongly suggesting the involvement of Gs proteins in the BK action. The BK-activated cAMP signalling system might be important for the observed inactivation of PKC slowly evoked by BK: the BK-induced rapid activation of PKC is decreased by dibutyryl cAMP, and the slow inhibition of PKC is prevented by an inhibitor of PKA, adenosine 3':5'-monophosphothioate (cyclic, Rp isomer). The inhibition of PKC translocation might be exerted directly at the level of PKC activation, since stimulation of phosphoinositide hydrolysis by BK was affected by neither dibutyryl cAMP nor forskolin. Thus our results provide the first evidence that A431 cells BK is able to activate two independent signal-transduction pathways via a single class of B2 receptors but two different G proteins. The lagging stimulation of the cAMP signalling pathway via Gs might serve to switch off PKC, which is rapidly activated via Gq-mediated stimulation of phosphoinositide hydrolysis.

The adenylate cyclase-inhibiting bradykinin receptor in guinea pig ileum membranes exhibits an unique antagonist profile

The purpose of the present study was to characterize more precisely an inhibitory, adenylate cyclase-coupled bradykinin receptor in guinea pig ileum membranes. Therefore, the effects of various well-known bradykinin B2 receptor antagonists were examined at the level of bradykinin-induced inhibition of ileal adenylate cyclase activity and compared with both their binding affinities and their potencies to antagonize ileal contraction evoked by bradykinin. A group of three highly potent antagonists was found to be able to antagonize both bradykinin-induced adenylate cyclase inhibition and smooth muscle contraction. Several other antagonists abolished the bradykinin-induced ileal contraction but did not influence its action on adenylate cyclase. The compound [D-Nal1, Thi5,8, D-Phe7]bradykinin which is known to inhibit the bradykinin-induced contraction in the rat uterus but not in the guinea pig ileum was found to be a weak but selective antagonist for the adenylate cyclase-coupled bradykinin receptor in guinea pig ileum. Altogether, in guinea pig ileum membranes the inhibitory, adenylate cyclase-coupled bradykinin B2 receptor with pM affinity towards bradykinin exhibits a unique antagonist profile and is distinguished from the excitatory bradykinin B2 receptor with nM affinity towards bradykinin.