Histamine H2 receptor overexpression induces U937 cell differentiation despite triggered mechanisms to attenuate cAMP signalling.

Knowing that cell-surface receptors that recognize and respond to extracellular stimuli are key components for the regular communication between individual cells required for the survival of any living organism, the aim of the present work was to investigate the effect of H2R overexpression on the U937 signal transduction pathway and its consequences on cell proliferation and differentiation. The overexpression of H2R led to an increase in cAMP basal levels, a leftward shift of agonist concentration-response curves, and similar maximal response to agonist treatment, suggesting that overexpressed H2Rs act as functional spare receptors. In this system cells triggered several mechanisms tending to restore cAMP basal levels to those of the naïve cells. H2R overexpression induced PDE activity stimulation and GRK2 overexpression. In spite of the onset of these regulatory mechanisms, H2 agonist and rolipram treatments induced the terminal differentiation of the H2R overexpressed clone, conversely to the naïve cells. Present findings show that stably H2R overexpression alters cAMP signalling as the result of not only the amounts of second messenger generated but also the activation or upregulation of various components of signalling cascade, leading to an adapted biologically unique system. This adaptation may represent an advantage or a disadvantage, depending on the biological system, but in any case, the existence of compensatory mechanisms should be considered when a clinical treatment is designed.

Human breast cell lines exhibit functional alpha2-adrenoceptors.

Adrenergic compounds (epinephrine and norepinephrine) are the most important hormones released during stress. Several different receptors are associated with their action in different tissues. However, alpha(2)-adrenoceptors have not yet been described in either normal or tumour human breast tissue. The aim of this work was to describe and characterize these receptors in several tumour and non-tumour human cell lines. The expression of alpha(2)-adrenoceptors was analyzed at the RNA (RT-PCR) and protein ([(3)H]-rauwolscine binding and immunocytochemistry) levels in different human breast cell lines, and the biological activity assessed by [(3)H]-thymidine incorporation. The cancer IBH-6, IBH-7 and MCF-7 and the non-tumour HBL-100 cells line, expressed both alpha(2B)- and alpha(2C)-adrenoceptor-subtypes. A single subtype was expressed in malignant HS-578T (alpha(2A)) and MDA-MB-231 and non-tumour MCF-10A cells (alpha(2B)). All cell lines exhibited significant binding for the specific antagonist [(3)H]-rauwolscine. The alpha-, alpha(2)-, and the alpha(1)-compounds with known affinity for alpha(2)-adrenoceptors, including epinephrine, norepinephrine, yohimbine, clonidine, rauwolscine and prazosin, competed significantly with binding in MCF-7 cells. In addition, IBH-6, IBH-7 and MCF-7 cells showed significant staining with specific antibodies against alpha(2B)- and alpha(2C)-adrenoceptor-subtypes, when tested by immunocytochemistry. In all cell lines, the specific agonist clonidine or oxymetazoline stimulated [(3)H]-thymidine incorporation. EC(50) values were in the range of 20-50 fM for IBH-6, IBH-7, and HS-578T; 0.14 pM for MCF-7; 2-82 pM for HBL-100 and MCF-10A cells, and a biphasic behaviour with a maximum value at 38.0 pM, was observed for MDA-MB-231 cells. The specific alpha(2)-adrenergic antagonist rauwolscine always reversed this stimulation at 0.1 nM. In conclusion, this study describes for the first time, the presence of alpha(2)-adrenoceptors in human epithelial breast cell lines. Moreover, activation of these receptors was associated with an enhancement of cell proliferation.

Three novel hormone-responsive cell lines derived from primary human breast carcinomas: functional characterization.

Human breast cancer primary cultures are useful tools for the study of several aspects of cancer biology, including the effects of chemotherapy and acute gene expression in response to different hormonal/chemotherapy treatments. The present study reports the conditions for primary culture of breast cancer samples from untreated patients and the most effective collagenization method to dissociate human samples consisting in an overnight incubation with 1 mg/ml types II or IV collagenase and further incubation in DMEM:F12 (1:1) medium supplemented with glutamine, bovine insulin, penicillin-streptomycin, HEPES, estradiol, cortisol (F), tri-iodothyronine (T(3)), transferrine (TR), and 10% fetal calf serum (FCS). These conditions proved to be appropriate for both primary culture and the development of stable cell lines. Of the seven cell lines obtained, three fast growing and estrogen receptor (ER)+/progesterone receptor (PgR)+/EGF receptor (EGFR)+ have been characterized. The cells are able to grow both in soft agar and in nude mice, and express cytokeratins, all parameters characteristic of malignant epithelial cell lines. The cells also exhibit an increased proliferation rate in the presence of estradiol, progesterone, and EGF, suggesting the presence of the corresponding receptors. The mRNA expression of type alpha- and beta-ER as well as EGFR, was confirmed by RT-PCR. In conclusion, the novel cell lines described, arose from primary tumors and are sensitive to estradiol, progesterone, and EGF. This not only expands the repertoire of breast cancer cells available as potentially useful tools for examining most parameters in breast cancer "in vitro", but also provides unique new models to explore the complex regulation by steroids as well as growth factors in such cells.

Angiotensin II phosphorylation of extracellular signal-regulated kinases in rat anterior pituitary cells.

We studied the effects of ANG II on extracellular signal-regulated kinase (ERK)1/2 phosphorylation in rat pituitary cells. ANG II increased ERK phosphorylation in a time- and concentration-dependent way. Maximum effect was obtained at 5 min at a concentration of 10-100 nM. The effect of 100 nM ANG II was blocked by the AT1 antagonist DUP-753, by the phospholipase C (PLC) inhibitor U-73122, and by the MAPK kinase (MEK) antagonist PD-98059. The ANG II-induced increase in phosphorylated (p)ERK was insensitive to pertussis toxin blockade and PKC depletion or inhibition. The effect was also abrogated by chelating intracellular calcium with BAPTA-AM or TMB-8 by depleting intracellular calcium stores with a 30-min pretreatment with EGTA and by pretreatment with herbimycin A and PP1, two c-Src tyrosine kinase inhibitors. It was attenuated by AG-1478, an inhibitor of epidermal growth factor receptor (EGFR) activation. Therefore, in the rat pituitary, the increase of pERK is a Gq- and PLC-dependent process, which involves an increase in intracellular calcium and activation of a c-Src tyrosine kinase, transactivation of the EGFR, and the activation of MEK. Finally, the response of ERK activation by ANG II is altered in hyperplastic pituitary cells, in which calcium mobilization evoked by ANG II is also modified.