The respective 27 kDa and 28 kDa protein kinase C substrates in vascular endothelial and MCF-7 cells are most probably heat shock proteins

Retinoic acid induced growth arrest of human breast carcinoma cells requires protein kinase C alpha expression and activity

Retinoic acid inhibits proliferation of hormone-dependent, but not hormone-independent breast cancer cells. Retinoic acid-induced changes in cellular proliferation and differentiation are associated with disturbances in growth factor signaling and frequently with changes in protein kinase C expression. PKC delta, epsilon, and zeta are expressed in both hormone-dependent (T-47D) and hormone-independent (MDA-MB-231) cell lines. Retinoic acid arrested T-47D proliferation, induced PKC alpha expression and concomitantly repressed PKC zeta expression. The changes in PKC alpha and PKC zeta reflect retinoic acid-induced changes in mRNA. In contrast, retinoic acid had no effect on growth, or PKC expression in MDA-MB-231 cells. Growth arrest and the induction of PKC alpha, but not the reduction in PKC zeta, resulted from selective activation of RAR alpha. In total, these results support an important role for PKC alpha in mediating the anti-proliferative action of retinoids on human breast carcinoma cells.

12-O-tetradecanoylphorbol-13-acetate inhibits aminophospholipid translocase activity and modifies the lateral motions of fluorescent phospholipid analogs in the plasma membrane of bovine aortic endothelial cells

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) is a potent mitogenic factor which can replace the growth promoting activity of basic fibroblast growth factor (bFGF) on bovine aortic endothelial cells. However, TPA-treated cells lose their strict contact inhibition at confluence, which is a characteristic of cells grown in the presence of bFGF. We have examined whether these changes could be related to modifications of the transbilayer and lateral motions of fluorescent lipids, namely 1-acyl-2-[6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl]-p hosphatidylcholine (C6-NBD-PC), -phosphatidylserine (C6-NBD-PS), and -phosphatidylethanolamine (C6-NBD-PE) inserted in the outer leaflet of the cell plasma membrane. In TPA-treated cells, the three fluorescent phospholipids remained located in the outer leaflet for at least 1 h at 20 degrees C after their insertion, indicating a blockade of the aminophospholipid translocase activity which is normally present in the plasma membrane of bFGF-treated cells. TPA also induced a large increase in the percentage of C6-NBD-PC and C6-NBD-PE probes which were free to diffuse laterally. The mobile fractions M reached values of approximately 100% for the two lipids, while for bFGF-treated cells they were found around 85 and 75%, respectively. For the C6-NBD-PS probe, M remained unchanged in bFGF and TPA-treated cells, at around 85%. TPA treatment also induced a twofold increase in the lateral diffusion coefficients of C6-NBD-PC and C6-NBD-PE, while that of C6-NBD-PS remained nearly unchanged. These effects of TPA may be related to the observed loss of differentiated properties of vascular endothelial cells and not to its mitogenic properties.

Photophysical and photobiological processes in the photodynamic therapy of tumours

Photodynamic therapy (PDT) is an innovative and attractive modality for the treatment of small and superficial tumours. PDT, as a multimodality treatment procedure, requires both a selective photosensitizer and a powerful light source which matches the absorption spectrum of the photosensitizer. Quadra Logic's Photofrin, a purified haematoporphyrin derivative, is so far the only sensitizer approved for phase III and IV clinical trials. The major drawbacks of this product are the lack of chemical homogeneity and stability, skin phototoxicity, unfavourable physicochemical properties and low selectivity with regard to uptake and retention by tumour vs. normal cells. Second-generation photosensitizers, including the phthalocyanines, show an increased photodynamic efficiency in the treatment of animal tumours and reduced phototoxic side effects. At the time of writing of this article, there were more than half a dozen new sensitizers in or about to start clinical trials. Most available data suggest a common mechanism of action. Following excitation of photosensitizers to long-lived excited singlet and/ or triplet states, the tumour is destroyed either by reactive singlet oxygen species (type II mechanism) and/or radical products (type I mechanism) generated in an energy transfer reaction. The major biological targets of the radicals produced and of singlet oxygen are well known today. Nucleic acids, enzymes and cellular membranes are rapidly attacked and cause the release of a wide variety of pathophysiologically highly reactive products, such as prostaglandins, thromboxanes and leukotrienes. Activation of the complement system and infiltration of immunologically active blood cells into the tumorous region enhance the damaging effect of these aggressive intermediates and ultimately initiate tumour necrosis. The purpose of this review article is to summarize the up-to-date knowledge on the mechanisms responsible for the induction of tumour necrotic reactions.

Phosphorylation of A 27-kDa protein correlates with survival of protein-synthesis-inhibited MCF-7 cells

Previously, we have shown that IGF-1, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and aurintricarboxylic acid (ATA) protected MCF-7 cells against death induced by the protein synthesis inhibitor cycloheximide (CHX). We proposed that phosphorylation of a putative cellular proteins(s) may be involved in this survival mechanism. In the present study we investigated the ability of several agents to induce phosphorylation of cellular proteins and correlated this ability to their survival effect. We found that TPA, ATA, and IGF-1 increased the degree of phosphorylation of a 27-kDa protein in a dose- and time-dependent manner in CHX-treated MCF-7 cells. The ED50 values observed were 25 ng/ml, 40 micrograms/ml and 15 ng/ml for TPA, ATA, and IGF-1, respectively. The effect was measured upon 10 min of cell treatment with each agent; it reached maximum at 60 min and thereafter decreased continuously to control levels. The 27-kDa protein was found in the cytosolic fraction as a phosphorylated serine residue. Further characterization with two-dimensional electrophoresis indicated that the 27-kDa phosphorylated serine residue. Further characterization with two-dimensional electrophoresis indicated that the 27-kDa phosphoprotein was resolved into two isoforms with pI 5.7 and 5.9. Such characteristics were observed for the small molecular weight heat shock protein HSP27. Indeed, a single band of 27 kDa was detected immunologically with rabbit polyclonal anti-human HSP27. The inactive phorbol ester alpha TPA, epidermal growth factor (EGF), and 8-bromoadenosine 3'5'-cyclic monophosphate (Br-cAMP) did not increase phosphorylation of the 27-kDa protein. Cell survival was measured by exposure of the CHX-pretreated cells to increasing concentrations of the various agents for 60 min, followed by a further incubation for 48 h in the presence of CHX only. TPA, ATA, and IGF-1 were found to enhance cell survival, whereas alpha-TPA, EGF and Br-cAMP did not. Our results indicate a correlation between phosphorylation of a 27-kDa protein, probably HSP27, and enhanced cell survival, suggesting a role for this phosphoprotein in the survival mechanism.

Expression of the small heat shock protein (hsp) 27 in human astrocytomas correlates with histologic grades and tumor growth fractions

1. Cellular expression and distribution of the stress response small heat shock protein 27 (hsp27) in 39 high-grade astrocytomas (27 glioblastoma multiformes, 12 anaplastic astrocytomas) and in 27 low-grade astrocytomas (grade I-II) were analyzed immunohistochemically. 2. The correlation between hsp27 expression and tumor growth fractions of the astrocytomas was examined following Ki-67 immunostaining. 3. The hsp27 staining was cell cytoplasmic. The hsp27 immunopositive rate was significantly higher in high-grade astrocytomas; the rates was 74% for glioblastomas, 58% for anaplastic astrocytomas, and 37% for low-grade astrocytomas. The small and large tumor cells, especially in glioblastomas, multinucleated tumor giant cells, tumor cells in the pseudopalisading and necrotic areas, cells of the microvascular endothelial proliferations, and tumor vascular smooth muscles were usually hsp27 positive. The mean percentage of hsp27-positive cells was significantly higher in the glioblastomas alone and in the combined high-grade astrocytomas, compared to the low-grade, and in recurrent rather than in primary high-grade astrocytomas. 4. The high-grade astrocytomas had a highly statistical significant Ki-67 labeling index. The Ki-67 labeling indices were significantly higher in the hsp27-positive than the hsp27-negative astrocytomas, irrespective of the histological grade. In the high-grade astrocytomas with a Ki-67 labeling index of five and above, 81% of those tumors were hsp27 positive. 5. Thus, a large number of human astrocytomas express hsp27, and hsp27 expression correlates with histological grades of astrocytoma and with tumor growth fractions. This being the case, hsp27 is likely to have a role in the growth of human astrocytomas.

Stathmin is a major substrate for mitogen-activated protein kinase during heat shock and chemical stress in HeLa cells

Stathmin is a ubiquitous, highly conserved 19-kDa cytoplasmic protein whose expression and phosphorylation are regulated in relation to cell proliferation, differentiation or activation, in many biological systems. In this report, we show that stathmin undergoes major phosphorylation in HeLa cells submitted to heat or chemical stress. Heat-shock-induced stathmin phosphorylation was very rapid, as maximal incorporation of phosphate was observed at 5 min. Phosphorylation of stathmin might, therefore, occur as a very early step in the intracellular response to heat shock. The sites of phosphorylation of stathmin involved during the stress response were identified as mostly Ser25 and, to a lesser extent, Ser38. These sites are both followed by a proline residue, and known to be good substrates in vitro for mitogen-activated protein kinase (MAP-kinase) and p34cdc2 kinase, respectively. In lysates from heat-shocked cells, an increased stathmin-kinase activity, distinct from the histone-H1-kinase activity, was found to phosphorylate stathmin mostly on Ser25, the main site for MAP-kinase in vitro. This stathmin-kinase coeluted quantitatively with the stress-activated MAP-kinase from an FPLC MonoQ column. Furthermore, a stathmin kinase activity was precipitated from lysates of heat-shocked HeLa cells by an anti-(MAP-kinase) serum. Together, these results indicate that the phosphorylation of stathmin by MAP-kinase is likely to be a significant component of the signalling array controlling the cellular response to stress, and they further underline the general involvement of stathmin in intracellular signalling.

Inhibitory effect of lead on the proliferation of cultured vascular endothelial cells

We investigated the effect of lead nitrate (0.5, 1.0, 2.0 or 5.0 microM) on the proliferation of cultured bovine aortic endothelial cells. After exposure to lead, the number of cells and the incorporation of [3H]thymidine into the acid-insoluble fraction of the cells were reduced in parallel in a concentration-dependent manner. Histologically, lead treatment resulted in a decrease in the cell number accompanied by a change in the cell shape from polygonal to spindle; however, no degenerative change was observed except in 5.0 microM lead-treated cells. Furthermore, stimulation of [3H]thymidine incorporation by either basic or acidic fibroblast growth factor was significantly reduced by lead. However, the leakage of lactate dehydrogenase into the medium from the cells, a marker of nonspecific cell damage, was not changed by lead. From these results, it was revealed that lead inhibits the proliferation of cultured vascular endothelial cells without nonspecific cell damage. Although lead does not destroy the monolayer of endothelial cells, the metal may exhibit its noxious effect in the repair process of the vascular endothelium.

Hormonal regulation of HSP27 expression in human endometrial epithelial and stromal cells

HSP27 has been analysed immunohistochemically in epithelium and stroma of premenopausal endometria obtained at different stages of the menstrual cycle and in endometria from postmenopausal women receiving oestrogens either alone or in combination with a progestin. The data indicate that HSP27 is increased by oestrogen and inhibited by progestins in glandular epithelium but not stroma. Oestrogen does not increase HSP27 in stromal cells and HSP27 is only present in stromal decidual cells seen in the late secretory phase where it continues to be detectable until the tenth week of gestation. Hormonal regulation of HSP27 is clearly different in endometrial epithelium and stroma and additional regulatory factors may be important as oestrogen alone does not increase postmenopausal epithelial HSP27 to the levels seen in the proliferative phase of premenopausal samples.

Endothelial cells and hyperthermia

Most radiation oncologists are aware of the effects of clinical hyperthermia on neoplastic cells. Its effects on blood vessels, however, are not as well recognized. Yet, since the 1960s a number of investigators have described and categorized the effects of hyperthermia on microvessels (in vivo), and on cultured endothelial cells (EC) (in vitro). Both EC and microvessels can be lethally damaged by the hyperthermia doses used as antineoplastic therapy. In vitro data indicate that capillary EC are moderately sensitive to hyperthermia. Proliferating EC are more thermosensitive suggesting that microvessels of malignant neoplasms (which contain many proliferating EC) are more affected than microvessels of normal tissues. This differential sensitivity of microvessels has also been observed in blood flow studies. Furthermore, hyperthermia inhibits angiogenesis. Thus, some of the antineoplastic effects of heat are caused by ischaemia due to obstruction or destruction of the tumour vessels or to inability to form new vessels. Sublethal EC damage can also be demonstrated, resulting in decreased synthesis of most proteins including adhesion molecules (as well as increased expression of a few such as heat shock proteins) and producing reversible loss of cytoskeletal elements. The therapeutic advantage provided by the higher thermal sensitivity of neoplastic vessels should be exploited further, perhaps by developing strategies specifically aimed to the tumour microvasculature.

Immunohistochemical localisation of the 25 kDa heat shock protein in unstressed rats: possible functional implications

The distribution of the 25 kDa heat shock protein (hsp 25) in a number of tissue types from unstressed rats was investigated. Immunohistochemical analysis showed that hsp 25 was not found in the thymus, brain (cerebral cortex and cerebellum), testis, adrenal, liver, spleen, or kidney. A number of cells in the anterior pituitary showed strong staining. These cells were tentatively identified as being either gonadotropes or thyrotropes. Strong staining was also observed in the blood vessels within these tissues. Hsp 25 was found to be localised predominantly to intestinal smooth muscle of the duodenum and colon and to vascular smooth muscle. Smooth muscle from other sites, such as the trachea, was also intensely stained. Lower and more variable amounts of staining were observed in cardiac and skeletal muscle. These observations suggest that hsp 25 is associated with cytoskeletal elements in muscle, and that the high staining intensity in smooth muscle might be due to the lack of internal architecture present in this muscle type.

Relationship of HSP27 and oestrogen receptor in hormone sensitive and insensitive cell lines

A 27 kDa heat shock (HSP27) has been analysed by immunoassay and immunoblotting in oestradiol sensitive and insensitive cells. Oestradiol growth responsive MCF7 and T47D human breast cancer cells and growth unresponsive variants derived therefrom have unaltered levels of HSP27 as well as retaining their oestradiol receptor phenotype. MCF7 cells induced to become doxorubicin resistant in culture lose both HSP27 and oestradiol receptor. Thus, in these three pairs of cells, HSP27 content parallels oestradiol receptor (ER). Analysis of a range of ER positive and negative human cell lines supports the positive relationship between HSP27 and ER. This included six ER positive and two ER negative breast tumour lines, one ER positive and one ER negative endometrial tumour cell line and seven ER negative human lines from other sites. One ER negative osteosarcoma line (HTB96) had appreciable levels of HSP27 that were unaffected after stable transfunction with an ER cDNA. Heat shock increases HSP27 levels in some but not all cell lines tested, the effect being inversely proportional to the basal (37 degrees C) content. In a mouse mammary tumour cell line, loss of androgen sensitivity was accompanied by loss of HSP27. Loss of HSP27 occurred in MCF7 cells made drug resistant to Novatrone, vincristine and etoposide as well as doxorubicin; no detectable change was seen in cells made resistant by 5 fluorouracil or X-irradiation. In ER positive ZR75 human breast tumour cells and in both ER negative and positive variants of the HTB96 human osteosarcoma line, the intracellular distribution of HSP27 was analysed. Over 96% of the HSP27 was in the cytosol fraction and the distribution was unaffected by incubation with oestradiol. HSP27 has been discussed in the literature under three different names p29, p24 and HSP27. The data presented in this paper are reviewed in the context of the previous data. It is concluded that there is a good but not absolute correlation between the presence of ER and high amounts of HSP27 but that low amounts of HSP27 are present in many ER negative cells. The correlations between HSP27 and drug resistance are more complex.

Rapid phosphorylation of 28-kDa heat-shock protein by treatment with okadaic acid and phorbol ester of BALB/MK-2 mouse keratinocytes

Protein phosphorylation by okadaic acid and 12-O-tetradecanoylphorbol-13-acetate (TPA) was examined using quiescent cultures of BALB/MK-2, a cell line derived from mouse epidermal keratinocytes. Treatment with okadaic acid caused rapid phosphorylation of five proteins with molecular masses of 65, 55, 50, 28 and 15 kDa (p65, p55, p50, p28, p15, respectively) while TPA caused rapid phosphorylation of five proteins with molecular masses of 80, 70, 40, 34 and 28 kDa (p80, p70, p40, p34, p28, respectively). In the present study, we examined p28, a common target protein of okadaic acid and TPA. The phosphorylation of p28 increased depending on time of exposure and doses of okadaic acid and TPA. Combined treatment with okadaic acid and TPA resulted in an additive effect. Its position on two-dimensional gel electrophoresis suggested that p28 is the 28-kDa heat-shock protein (HSP28). This possibility was confirmed by migration of p28 with HSP28 and comparative peptide mapping of the two proteins. The phosphoamino-acid residue of phosphorylated HSP28 was serine. In two-dimensional tryptic peptide maps, the same peptides were phosphorylated after treatment with both okadaic acid and TPA.

Expression of the murine small heat shock proteins hsp 25 and alpha B crystallin in the absence of stress

Stress induces the synthesis of several large and small heat shock proteins (hsp's). Two related small hsp's, hsp25 and alpha B crystallin exist in mice. alpha B crystallin is an abundant protein in several tissues even in the absence of stress. Particularly high amounts accumulate in the eye lens. Here we show that hsp25 is likewise constitutively expressed in many normal adult tissues. In the absence of stress the protein is most abundant in the eye lens, heart, stomach, colon, lung, and bladder. The stress-independent expression pattern of the two small hsp's is distinct. In several tissues the amount of hsp25 exceeds that accumulating in NIH 3T3 fibroblasts in response to heat stress. hsp25, like alpha B crystallin, exists in a highly aggregated form in the eye lens. The expression of hsp25 and alpha B crystallin in normal tissues suggests an essential, but distinct function of the two related proteins under standard physiological conditions.

Effect of hyperosmolality on alkaline phosphatase and stress-response protein 27 of MCF-7 breast cancer cells

MCF-7, a continuous cell line derived from a human breast carcinoma, exhibits very low alkaline phosphatase (ALP) activity. The enzyme is heat-stable and is inhibited by L-phenylalanine and L-phenylalanylglycylglycine, but not by L-homoarginine, 1-bromotetramisole, or levamisole. These data indicate that MCF-7 produces term-placental ALP, the oncodevelopmental enzyme form inappropriately expressed by a variety of human tumors. In contrast to human cancer cells that produce this enzyme monophenotypically, ALP activity of MCF-7 cells is not significantly increased by glucocorticoids or sodium butyrate. By comparison, exposure to hyperosmolality causes a striking increase in enzyme activity. Cycloheximide blocks this effect. The results obtained with cell-free assays were confirmed by cytochemical and immunocytochemical assays on whole cells. Because some of the agents tested in the enzyme modulation experiments affect cell proliferation, their possible effect on two stress-response proteins (srp 27 and srp 72) was also examined; specific immunocytochemical assays were used. These tests revealed that neither protein is affected by glucocorticoids; that sodium butyrate has no effect on srp 27, but alters the intracellular distribution of srp 72; and that hyperosmolality, while not significantly affecting srp 72, causes an increase in srp 27.

Cell-free phosphorylation of the murine small heat-shock protein hsp25 by an endogenous kinase from Ehrlich ascites tumor cells

The small heat-shock protein hsp25 of the Ehrlich ascites tumor exists in one non-phosphorylated (hsp25/1) and two phosphorylated (hsp25/2, hsp25/3) isoforms. In stationary phase tumor cells, a protein kinase activity was detected which phosphorylates hsp25/1, resulting in the formation of several phosphorylated hsp25 isoforms, including those occurring naturally in the tumor. Cell-free phosphorylation of hsp25 required Mg2+ and ATP and was independent of Ca2+, phosphatidylserine, cAMP and cGMP. Polymyxin B inhibited, specifically, hsp25 phosphorylation, whereas trifluoperazine, staurosporine and the protein inhibitor of protein kinase A had no effect. In its properties, the hsp25 phosphorylating kinase differs from other common kinases such as protein kinases A and C, calcium/calmodulin-dependent kinases, and the ribosomal protein S6 kinase.

Expression of 27-kD heat-shock protein isoforms in human neoplastic and nonneoplastic liver tissues

Previous study of rat liver during chemically induced hepatocarcinogenesis has shown that expression of isoforms of the 27-kD heat-shock protein was greater in neoplastic nodules and in hepatocellular carcinoma than in control livers. In this study, various human neoplastic and nonneoplastic liver tissues were investigated with electrophoresis after amino acid labeling to evaluate the expression of 27-kD heat-shock protein isoforms. This revealed that human liver contains 27-kD proteins that are recognized by a polyclonal antibody raised against human 27-kD heat-shock protein. Basal levels of fluorographical and immunostaining intensity of the 27-kD heat-shock protein spots (respectively, after [3H]leucine or 32P incorporation or as checked with a specific human 27-kD heat-shock protein antibody) were higher in hepatomas than in non-tumorous liver. Phosphorylation patterns of the 27-kD heat-shock protein isoforms were, however, similar in hepatocellular carcinoma and in uninvolved surrounding liver. Heat inducibility of the 27-kD heat-shock protein, tested in one case of liver cell adenoma and in the surrounding liver, was also preserved in both tissues. The role of the overexpression of 27-kD heat-shock protein in neoplastic liver tissues remains unknown. We propose, as a working hypothesis, that it is related to the resistant phenotype acquired by some tumors during malignant progression.

Reduced guanine nucleotide-stimulated polyphosphoinositide specific phospholipase C in platelet hyperaggregation in IDDM

Platelet activity is increased in persons with insulin dependent diabetes mellitus (IDDM). Receptor-medicated phospholipase C (PLC) activation and hydrolysis of phosphatidylinositol bisphosphate (PIP2) accompanies platelet activation. Previous work from our laboratory has shown that PIP2 hydrolysis is decreased in platelets of persons with IDDM. PIP2 hydrolysis is mediated via a phosphoinositide(PI)-specific PLC. PI-PLC activity is regulated by guanine nucleotide(GTP)-binding proteins. We therefore examined the hypothesis that platelet aggregations and PI turnover in platelet from subjects with IDDM is linked to alterations in PI-specific PLC activity. We found thrombin induced platelet aggregation was increased in the IDDM group. Basal PI and PIP2-specific PLC activity was not statistically different for the two groups. Guanine-nucleotide stimulated PIP2-specific PLC activity was decreased in the IDDM platelets. The mechanism for the reduced PLC activity and its role in the platelet hyperaggregation requires further study.

The 29-kDa proteins phosphorylated in thrombin-activated human platelets are forms of the estrogen receptor-related 27-kDa heat shock protein

Thrombin plays a critical role in platelet activation, hemostasis, and thrombosis. Cellular activation by thrombin leads to the phosphorylation of multiple proteins, most of which are unidentified. We have characterized several 29-kDa proteins that are rapidly phosphorylated following exposure of intact human platelets to thrombin. A murine monoclonal antibody raised to an unidentified estrogen receptor-related 29-kDa protein selectively recognized these proteins as well as a more basic, unphosphorylated 27-kDa protein. Cellular activation by thrombin led to a marked shift in the proportion of protein from the 27-kDa unphosphorylated form to the 29-kDa phosphoprotein species. Using this antibody, we isolated and sequenced a human cDNA clone encoding a protein that was identical to the mammalian 27-kDa heat shock protein (HSP27), a protein of uncertain function that is known to be phosphorylated to several forms and to be transcriptionally induced by estrogen. The 29-kDa proteins were confirmed to be phosphorylated forms of HSP27 by immunoprecipitation studies. Thus, the "estrogen receptor-related protein" is HSP27, and the three major 29-kDa proteins phosphorylated in thrombin-activated platelets are forms of HSP27. These data suggest a role for HSP27 in the signal transduction events of platelet activation.

Phosphorylation of the stress protein hsp27 is an early event in murine myelomonocytic leukemic cell differentiation induced by leukemia inhibitory factor/D-factor

Leukemia inhibitory factor/D-factor, a potent differentiation-inducing glycoprotein for murine myelomonocytic leukemic M1 cells, rapidly stimulated the phosphorylation of a 27 kDa protein with an isoelectric point of 5.6 in a LIF-sensitive M1-T22 cell line but not in a LIF-resistant M1-D(-) cell line. The increase in phosphorylation was detectable 5 min after LIF treatment and was maximal at 10 min. Heat shock treatment at 44.5 degrees C for 30 min also induced the phosphorylation of the same 27 kDa protein. Although this 27 kDa protein did not become labeled with [35S]-methionine, metabolic labeling experiments using [35S]-cysteine or [3H]-leucine clearly demonstrated that the synthesis of this protein was enhanced after heat shock. These results suggest that the phosphorylated 27 kDa protein is a low molecular weight stress protein and that the protein may play a role at an early stage in the LIF signaling pathway probably linked to macrophagic differentiation.

Activation of protein kinase C by phorbol esters induces DNA synthesis and protein phosphorylations in glomerular mesangial cells

The tumor-promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) is shown to be mitogenic for quiescent glomerular mesangial cells cultured in serum-free conditions. TPA induces DNA synthesis measured by [3H]thymidine incorporation in a dose-dependent manner with an ED50 of 7 ng/ml and an optimal response for 50 ng/ml. The phorbol ester action is potentiated by insulin with an increase of the maximal effect from 232 +/- 15% for TPA alone to 393 +/- 96% for TPA plus insulin. Down-regulation of protein kinase C by prolonged exposure to TPA completely abolishes the mitogenic effect of the phorbol ester. Using a highly resolutive 2D electrophoresis, we have shown that TPA is able to stimulate the phosphorylation of 2 major proteins of Mr 80,000, pl 4.5 (termed 80K) and Mr 28,000, pI 5.7-5.9 (termed 28K). The 80K protein phosphorylation is time- and dose-dependent with an ED50 of 8 ng/ml TPA. Exposure of mesangial cells to heat-shock induces synthesis of a 28K protein among a set of other proteins suggesting that the 28K protein kinase C substrate belongs to the family of low molecular mass stress proteins. Mitogenic concentrations of TPA and phorbol 12,13-dibutyrate inhibit [125 I]epidermal growth factor binding and stimulate the 80K protein phosphorylation with the same order of potency. The inactive tumor-promoter 4 alpha-phorbol was found to be ineffective both on these 2 parameters and on DNA synthesis. These results suggest a positive role for protein kinase C on mesangial cell proliferation and indicate the existence in this cell line of 2 major protein kinase C substrates.

Gossypol effects on endothelial cells and tumor blood flow

Isomers (-, +) of the antitumor agent gossypol (G) were studied for their ability to reduce tumor ATP and blood flow in rats bearing subcutaneously implanted pancreatic tumors. A 50% reduction in tumor ATP/Pi within ih of a single injection of -G was associated with a 60% decline in tumor blood flow. To determine if these changes in tumor physiology could be due to a direct drug effect on tumor endothelium, G isomers were compared for their ability to alter protein (125I-BSA) permeability and metabolic (32P) labelling of cultured endothelial cells. Treatments for ih produced no endothelial cell leakage, but 24h exposures to either -G (5 microM) or +G (50 microM) produced complete permeability of the monolayers to 125I-BSA. In contrast, 0.5-I.Oh exposures to -G (4 microM) produced 2 to 3-fold increases in phosphorylated 27 kDa heat-shock protein, hsp-27. Hsp-27 phosphoprotein isoforms were differentially labelled following -G and +G exposures with the phosphorylation profile of -G appearing most similar to that of oxyradical producing agents known to induce hsp-27 and injure endothelial cells. We postulate that the tumor ischemic effects of -G are mediated by endothelial response to oxyradical production in a mechanism similar to that of tissue ischemia-reperfusion injury.

Basic fibroblast growth factor stimulates glomerular mesangial cell proliferation through a protein kinase C-independent pathway

Basic Fibroblast Growth Factor (bFGF) is shown to be a potent mitogen for cultured glomerular mesangial cells. bFGF induces an increase in cell number and stimulates DNA synthesis measured by [3H]thymidine incorporation in normal as well as in protein kinase C-depleted cells. The ED50 observed in both cases are nearly identical (approximately 0.04 nM) and maximal responses are obtained at 1 nM. Staurosporine, a potent protein kinase C inhibitor, does not prevent bFGF from inducing mitogenesis. On the contrary, the tumour promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) and the bradykinin derivative Des-Arg9bradykinin that we have previously shown as mitogens for mesangial cells, fail to trigger DNA synthesis or cell proliferation upon staurosporine treatment or in protein kinase C-depleted cells. bFGF is unable to induce the association of the enzyme to membranes, the so-called translocation process, although the growth factor induces a slight production of diacylglycerol. Using a highly resolutive two-dimensional electrophoresis, we show that bFGF, in contrast to TPA, is unable to stimulate the phosphorylation of a Mr 80,000/pI 4.5 protein, a major and specific protein kinase C substrate. By contrast, bFGF stimulates the phosphorylation of a Mr 28,000/pI 5.7-5.9 protein in normal as well as in protein kinase C-depleted cells while TPA induces this protein phosphorylation only in normal cells. Our results suggest that bFGF exerts its proliferative action on mesangial cells through a protein kinase C-independent pathway and that the growth factor does not activate anyway the enzyme in this cell type.