Biochemical characterization of FMDV A10 and A22 subtypes by PAGE and IEF

Both polyacrylamide gel electrophoresis (PAGE) and iso-electric focusing (IEF) have been standardized using the sucrose density gradient purified 146S particles of FMD virus subtypes A10 and A22. Differences in the molecular weights of structural proteins (VP1, VP2 and VP3 of two subtypes (A10 and A22) of FMDV have been revealed in PAGE but no appreciable differences in the pI of VP1, VP2 and VP3 is found in IEF.

Polymorphism, distribution, and segregation of AFLP markers in a doubled haploid rice population

We exploited the newly developed amplified fragment length polymorphism (AFLP) technique to study the polymorphism, distribution and inheritance of AFLP markers with a doubled haploid rice population derived from 'IR64'/'Azucena'. Using only 20 pairs of primer combinations, we detected 945 AFLP bands of which 208 were polymorphic. All 208 AFLP markers were mapped and distributed over all 12 chromosomes. When these were compared with RFLP markers already mapped in the population, we found the AFLP markers to be highly polymorphic in rice and to follow Mendelian segregation. As linkage map of rice can be generated rapidly with AFLP markers they will be very useful for marker-assisted backcrossing.

Adenosine-mediated inhibition of casein production by mouse mammary glands in culture

The present study was carried out to examine whether activation of adenosine receptors by adenosine analogues will affect casein production by mouse mammary epithelial cells. The morphogenesis and functions of epithelial tissue in the mammary gland are influenced by their surrounding adipocytes. Adipocytes are known to release adenosine into the extracellular fluid which can modulate cyclic-AMP levels in surrounding cells through binding to their adenosine receptors. To examine a possible paracrine effect of adenosine, the modulation of casein production in mammary explant culture and mammary epithelial cell (MEC) culture by adenosine receptor agonists has been investigated. We have observed that activation of the A1-adenosine receptor subtype in mammary tissue by an adenosine analogue (-)N6-(R-phenyl-isopropyl)-adenosine (PIA) raised cAMP levels. PIA and another adenosine receptor agonist, isobutylmethylxanthine (IBMX), inhibited casein accumulation both in explants and in MEC cultures in the presence of lactogenic hormones, which suggests that PIA or adenosine can act directly on the epithelial cells. This inhibition does not appear to be caused by elevation of cAMP levels or phosphodiesterase activity. The inhibition of intracellular casein accumulation by PIA and IBMX in explant cultures can be reversed via treatment of pertussis toxin which is known to ADP-ribosylate GTP-binding G alpha i-proteins, indicating that a Gi-protein-dependent pathway may be involved in this inhibition. The results also suggest that local accumulation of adenosine in the extracellular fluids of mammary glands is likely to inhibit the lactogenic response of mammary epithelial cells.

Cell proliferation and apoptosis during mammary carcinogenesis in pituitary isografted mice

In the present study, pituitary isografted animals serve as a model for evaluating the changes in differentiation, cell proliferation and programmed cell death (apoptosis) in mammary epithelial cells during carcinogenesis. The percentage of bromodeoxyuridine (BrdU)-labeled ductal and alveolar cells was significantly higher in pituitary isografted animals than in non-isografted control animals. BrdU-labeled cells increased in lobular hyperplastic nodules, keratinized nodules and mammary carcinomas; similar changes were observed with apoptotic cells, which were rare in mammary glands of adult non-isografted animals (one to three apoptotic cells per 2000 mammary epithelial cells), but their number increased in hyperplastic lesions and mammary carcinomas. Among hyperplastic nodular lesions, variants with high, moderate and low proliferative activity and/or apoptotic cell death were identified, which suggests that they may have different growth potentials and different propensities for malignant transformation. After removing pituitary isografts, apoptosis occurs in hyperplastic lesions but not in mammary carcinomas-implying that malignant tumors are hormone-independent. The dynamics of the changes in apoptotic cell death among various hyperplastic lesions after removal of pituitary isografts suggests that these lesions are composed of heterogeneous cell populations, as far as the initiation of apoptosis is concerned. Our data indicate that apoptosis can be used together with cell proliferation as a potential marker in characterizing the growth potential and phenotypic diversity of hyperplastic, premalignant and malignant mammary gland lesions.

N-Ethyl-N-nitrosourea induces mammary cancers in the pituitary-isografted mouse which are histologically and genotypically distinct from those induced by N-methyl-N-nitrosourea

N-Ethyl-N-nitrosourea (ENU) and N-methyl-N-nitrosourea (MNU) are alkylating agents which respectively ethylate or methylate nucleophilic centers in the cell such as DNA. In vitro studies with naked DNA and bacterial mutagenesis assays suggest that these two compounds induce different spectra of genetic lesions. In addition, the ethyl-DNA adducts induced by ENU persist longer than the methyl-DNA adducts induced by MNU. Since MNU is a known mammary carcinogen in the pituitary-isografted mouse, these data suggest that ENU may be an even more potent carcinogen than MNU. The purpose of this study was to determine whether ENU was a mammary carcinogen in the pituitary-isografted mouse and if so, to compare the genotype and phenotype of ENU-induced mammary tumors with those induced by MNU. Fifteen adult female virgin BALB/c mice were isografted with two pituitaries and subsequently treated with a single intravenous injection of ENU (50 micrograms/g body weight). Mammary adenocarcinomas arose in all of the survivors (n=12) with a median latency of 27 weeks and a mean frequency of 1.4 cancers per mouse. When tumor DNA was analyzed for mutations in the 12th and 61st codons of c-Ki-ras or c-Ha-ras protooncogenes, only wild type sequences were found. This is in contrast to MNU which causes a G to A transition mutation in the 12th codon of the c-Ha-ras proto-oncogene in about one of five mammary cancers induced in pituitary-isografted mice. Furthermore, the ENU-induced tumors were solid viable papillary adenocarcinomas, whereas MNU induced tumors are highly necrotic adenocarcinomas with squamous metaplasia. These results demonstrate that, in the pituitary-isografted mouse, ENU is as potent a mammary carcinogen as MNU and suggest that oncogenes other than c-Ki-ras or c-Ha-ras may be involved in ENU-induced mammary cancers.

Hormone dependent and independent mammary tumor development form N-methyl-N-nitrosourea-treated rat mammary epithelial cell xenografts in the nude mouse: multiple pathways and H-ras activation

A nude mouse mammary fat pad xenograft system was developed to examine hormone dependent and independent mammary tumorigenesis and progression from N-methyl-N-nitrosourea (MNU)-induced hyperplastic lesions. Ninety-one percent of transplanted mammary tumors grew, with an orthotopic preference, and maintained their hormone dependence, histopathology, and H-ras mutation frequency. Grafted mammary epithelial cells, from MNU-treated rats, developed normal; and hyperplastic outgrowths, representative of those found in the rat mammary gland after MNU-treatment. Hyperplasias developed into neoplasias that were both hormone dependent and independent. We demonstrate that hormone independent tumors can develop directly either from lobuloalveolar or ductal hyperplasias or from hormone dependent tumors. H-ras mutation was detected in mammary preneoplasias (4 lines) before they developed into tumors and was associated with an elevated tumorigenic potential. Our observations suggest that there are multiple histopathogenic pathways in the development and progression to hormone independent rat mammary tumors.

Isolation of a cDNA for the human homolog of MAT-1 oncogene and its expression in human breast cancer cells

Overexpression of mouse MAT-1 oncogene is associated with carcinogensis of mouse mammary epithelial cells. A human cDNA (hMAT) homologous to MAT-1 was isolated from normal human breast tissue. The hMAT cDNA is 1312 bp long and produces a 8.5 kDa peptide in vitro. The hMAT probe hybridized with 2.5 kb RNA in normal human breast epithelial cells from reduction mammoplasty specimens and in human breast cancer cell lines. The extent of hMAT gene expression in human breast cancer cell line was variable, with BT-20, T47-D, and MDA-MB-231 showing about a 10-fold overexpression compared to primary normal human breast epithelial cells, MCF-7, and ZR-75-1.

Adenoviral-mediated gene transfer into primary human and mouse mammary epithelial cells in vitro and in vivo

Primary mammary epithelial cells from both the human and mouse mammary glands can be genetically altered under a variety of situations using the replication-defective adenoviral vector containing a marker gene encoding the E. coli beta-galactosidase. Primary human and mouse mammary epithelial cells in monolayer culture and in three-dimensional collagen gel culture systems were transduced by adenovector at high efficiency. Successful gene transfer was also accomplished in situ and in vivo. In the mouse mammary gland, anatomically restricted gene transfer and expression was demonstrated by micro-injection of adenoviral vector directly into the main duct of the mammary gland. Injection of adenoviral vector directly into the human mammary tissues from reduction mammoplasty specimens, into the mouse mammary gland-free fat pad containing the previously transplanted dissociated human mammary epithelial cells, and intratumorally into the human breast cancer xenografts in nude mice, all resulted in successful gene transfer to human mammary epithelial cells. High efficiency introduction of genetic material into primary mammary epithelial cells is important in the study of mammary carcinogenesis and potentially for gene therapy of human breast cancer.

Refractoriness to mammary tumorigenesis in parous rats: is it caused by persistent changes in the hormonal environment or permanent biochemical alterations in the mammary epithelia?

Administration of a single i.v. injection of 50 mg N-methyl-N-nitrosourea (MNU)/kg body wt to 50- to 60-day old virgin rats, 120-day-old virgin rats, and 120-day-old parous rats (Sprague-Dawley; n = 18-37) resulted in a high incidence of mammary carcinomas in the virgin animals (97.3% in 50- to 60-day-old virgin rats; 75.0% in 120-day-old virgin rats), but mammary carcinomas did not develop in the parous rats. The concentrations in serum of various mammotropic hormones were measured in identical groups of rats at the time of MNU treatment. Growth hormone (GH) concentration was significantly reduced in parous rats, as compared with young or age-matched virgin rats. The concentrations of prolactin, 17 beta-estradiol, progesterone, corticosterone and thyroxine were not significantly altered in the parous rats compared to the two groups of virgin animals. Histological examination of the mammary glands from the three groups of rats showed that the epithelia of the parous animals were in a stage of regression, whereas the mammae of the young virgin rats showed the highest degree of lobulo-alveolar development. The levels of estrogen receptor (ER), epidermal growth factor (EGF) receptor (EGF-R) and GH receptor (GHR) in the mammary glands of the animals were also measured. We found a reduction in the receptor levels for both estrogen and EGF in mammary tissues from parous animals. Receptors for GH were present in normal mammary tissues from both virgin and parous rats. We hypothesize that the reduction in the circulating concentration of GH caused the reduced susceptibility of parous rats to mammary carcinogenesis possibly by decreasing the levels of ER and/or EGF-R in the mammary gland.

Partial purification and characterization of a soluble protein phosphatase from Leishmania donovani promastigotes

A soluble protein phosphatase from the promastigote form of the parasitic protozoan Leishmania donovani was partially purified using Sephadex G-100, DEAE-cellulose and again Sephadex G-100 columns. The partially purified enzyme showed a native molecular weight of about 42,000 in both Sephadex G-100 and sucrose density gradient centrifugation. The sedimentation constant, stokes radius and frictional ratio were found to be 3.43S, 2.8 nm and 1.20 respectively. The enzyme preferentially utilized phosphohistone as the best exogenous substrate. Mg2+ ions were essential for enzyme activity; among other metal ions Mn2+ can replace Mg2+ to a certain extent whereas Ca2+, Co2+ and Zn2+ could not substitute for Mg2+. The pH optimum of the enzyme was 6.5-7.5 and the temperature optimum 37 degrees C. The apparent Km for phosphohistone was 7.14 microM. ATP, ADP, inorganic phosphate and pyrophosphate had inhibitory effect on the enzyme activity whereas no inhibition was observed with sodium tartrate and okadaic acid. These results suggest that L. donovani promastigotes possess a protein phosphatase which has similar characteristics with the mammalian protein phosphatase 2C.

Reconstituted human normal breast in nude mice using collagen gel or Matrigel

Human breast epithelial cells dissociated from reduction mammoplasty specimens were embedded in two commonly used extracellular matrices, type I collagen gel or Matrigel, and subsequently transplanted subcutaneously into athymic nude mice. Histological sections from both types of recovered gels showed epithelial structures arranged as short tubules with some branching as well as preservation of epithelial cell polarity. Proliferation was studied in vivo by 5-bromo-2'-deoxy-uridine labeling followed by immunostaining of sections from recovered gels. Human breast epithelia embedded in collagen gel or Matrigel had similar proliferative activity. Cholera toxin, 17 beta-estradiol, and epidermal growth factor, when tested singly, were growth promoting, and in combination 17,beta-estradiol and cholera toxin had an additive effect but 17,beta-estradiol and epidermal growth factor were not additive. Our model system provides a means to study the endocrine control of normal human breast development.

Multifunctional phosphatidic acid signaling in mammary epithelial cells: stimulation of phosphoinositide hydrolysis and conversion to diglyceride

We have shown previously that phosphatidic acid esterified to polyunsaturated fatty acids is mitogenic for primary cultures of mouse mammary epithelial cells embedded within collagen gels. We hypothesized that this mitogenic competence resulted from the ability of this phospholipid to activate multiple signal transduction pathways in mammary epithelium. A closer examination of this hypothesis was undertaken by examining the effect of exogenous phosphatidic acid on phosphoinositide (PI) hydrolysis and its intracellular metabolism to diglyceride, an activator of protein kinase C. For assays of phosphoinositide-specific phospholipase C activation, mammary epithelial cells from virgin Balb/c mice were isolated by collagenase dissociation of mammary glands and cultured on the surface of Type I collagen-coated culture dishes. Phosphatidic acid (PA) stimulated a sustained increase in inositol phosphates and caused inositol phospholipid depletion when added to cells in which inositol phospholipids were prelabeled with 3H-myoinositol. This effect was specific for PA among phospholipids tested. Neither lineoleic acid, that can be released from PA, nor prostaglandin E2 affected PI hydrolysis. When mammary epithelial cells were cultured inside collagen gels in the presence of exogenous PA or phosphatidylcholine (PC) radiolabeled with 3H-glycerol, PA was found to persist intracellularly and be dephosphorylated to diglyceride (an activator of protein kinase C) to a greater extent than PC, a nonmitogenic phospholipid. In contrast to PA, epidermal growth factor (EGF) only slightly stimulated PI hydrolysis, showing that these two different growth-promoting factors do not actively couple to the same signal transduction pathways in mammary epithelial cells. These results show that PA may activate multiple pathways in mammary epithelial cells either directly or via its metabolism to diglyceride.

Hormones and mammary carcinogenesis in mice, rats, and humans: a unifying hypothesis

An attempt has been made to put forward a unifying hypothesis explaining the role hormones play in the genesis of mammary cancers of different phenotypes and genotypes in mice, rats, and humans. Most mammary cancers in these species originate in luminal mammary epithelial cells lining the mammary ducts and alveoli. These cancers are histopathologically diverse and are classified on the basis of growth requirements as hormone-dependent or hormone-independent tumors. In most strains of mice, mammary cancers at the time of detection are largely of the hormone-independent type; in rats, almost all mammary cancers are hormone-dependent, while humans have both phenotypes. In spite of these differences, in vivo studies show that hormones (ovarian and pituitary) are essential for luminal mammary epithelial cell proliferation and also for the development of mammary cancers of both hormone-independent and hormone-dependent types. This article, based on our extensive in vivo and in vivo studies and on current literature, proposes a model to explain the central role of hormones in the genesis of all types of mammary cancers. The model attempts to address the following questions: (i) how hormones regulate luminal mammary epithelial cell proliferation, (ii) why hormones are required for the genesis of mammary cancers of all phenotypes and genotypes, including those which are always classified as hormone-independent tumors, and (iii) why the three species (mouse, rat, and human) have consistently different ratios of hormone-dependent to hormone-independent tumors.

Refractoriness to mammary carcinogenesis in the parous mouse is reversible by hormonal stimulation induced by pituitary isografts

We have previously reported that mouse mammary epithelial cells transformed in vitro yield tumors which vary qualitatively and quantitatively as a function of the mitogenic environment in which the cells are propagated at the time of carcinogen treatment. One milieu supportive of transformation in vitro was medium supplemented with progesterone and prolactin as the mitogens. We have performed parallel studies in which virgin mice were isografted with pituitaries resulting in elevated serum titers of progesterone and prolactin. After carcinogen treatment, these mice developed mammary tumors which included those identical genotypically and phenotypically to tumors induced in vitro in cells grown in progesterone and prolactin during carcinogen exposure. Our current working hypothesis is that the mitogenic environment around the time of carcinogen administration can modulate the incidence and phenotype of the resultant tumors. To further test this hypothesis, we have evaluated the susceptibility of hormonally-stimulated parous mice to chemically induced mammary carcinogenesis since parity is known to significantly reduce the susceptibility of the mouse mammary gland to carcinogenesis. Virgin or multiparous BALB/c mice were isografted with two pituitaries. Five weeks after surgery, the mice were injected with N-methyl-N-nitrosourea (MNU; 50 micrograms/g i.v.). Mammary carcinomas arose in 85% (11/13) with a median latency of 22.8 weeks and 1.9 tumors per virgin mouse and 80% (24/30) with a median latency of 22.1 weeks at a frequency of 1.9 tumors per parous mouse. Only 14% (2/14) of the non-isografted, age-matched parous controls developed tumors when injected with MNU. Fourteen parous mice receiving only pituitary isografts (no MNU), did not develop mammary carcinomas within the 7-month period of the study. These results demonstrate that parous BALB/c mice are refractory to MNU-induced mammary carcinogenesis and that this refractoriness is not permanent, but can be overcome by hormonal stimulation mediated by pituitary isografts.

In vivo growth stimulation of collagen gel embedded normal human and mouse primary mammary epithelial cells

A new system for studying growth of normal human mammary epithelial cells in an in vivo environment using athymic nude mice is described. Human mammary epithelial cells dissociated from reduction mammoplasty specimens were embedded within collagen gels and subsequently transplanted subcutaneously into nude mice. Histological sections of recovered collagen gels showed epithelial cells arranged as short tubules with some branching. Proliferation of mammary epithelial cells was quantitated in vivo by 3 days' continuous infusion with 5 bromo-2'-deoxy-uridine followed by immunostaining of sections from recovered gels. Ovarian steroids administered to the host animals, resulting in blood serum levels normally found in the human female, had little or no effect on the proliferation of human mammary epithelial cells. Collagen gel embedded mouse mammary epithelial cells, mouse mammary explants, and host mammary glands all responded similarly to ovarian steroids, suggesting that the unresponsiveness of the human mammary epithelial cells under these conditions was not due to dissociation per se. However, an increased dose of 17 beta-estradiol or a growth factor combination containing epidermal growth factor, cholera toxin, and cortisol significantly stimulated the proliferation of human outgrowths. The growth factor response was dependent on the location of the cells, with the greatest response seen in the part of the gel proximal to the osmotic pump delivering the growth factors and the effect gradually waning in area more distal to the pump. The effect was especially striking since the mitotic figures could be easily identified and the labeling index was as high as 75%. The host mouse mammary gland also responded to growth factors, resulting in ductal hyperplasia. The proliferative and morphogenetic effects of various agents on normal human mammary epithelial cells embedded in collagen gel can be studied in vivo in nude mice.

Effect of reproductive states on lipid mobilization and linoleic acid metabolism in mammary glands

Effects of pregnancy and lactation on lipid metabolism in mouse mammary fat pads and nonmammary adipose tissues have been studied. In order to address the question whether the influence of hormonal milieu on lipid metabolism in mammary epithelial cells during pregnancy and lactation is the same as in fat cells, we have studied the mobilization of lipids and metabolism of fatty acids in the intact mammary glands, parenchyma-free mammary fat pads and in the perimetrial fat tissues of virgin, pregnant and lactating mice. Compared to parenchyma-free mammary fat pads, the perimetrial adipose tissues accumulated 5-fold higher levels of triglycerides during pregnancy. Mammary fat cells maintained overall lipid levels during pregnancy and lactation (16-20 micrograms/fat pad). In contrast, lactation depleted total lipid stores from 108 +/- 5 to 24 +/- 4.5 micrograms/fat pad in perimetrial fat pads. Results of comparative analysis of fatty acid composition of mammary fat pads, with and without epithelial tissue, from virgin and lactating mice showed stimulation of 18:2 omega 6 metabolism leading to 130% increase in the ratio 20:4 omega 6 to 18:2 omega 6 in the epithelial compartment. Pregnancy and lactation resulted in the elevation of 20:4 omega 6 levels probably due to a 4-fold increase in delta 5 desaturase activity and a decrease in oxidative degradation of 18:2 omega 6. These results suggest that, unlike other adipose tissues, the metabolic pathways in mammary fat cells are not dedicated to sequestration and accumulation of dietary lipids during pregnancy. Lactation favors mammary epithelial cell-stimulated production of precursors of eicosanoids which are known to have agonist-like effect on mammary epithelial cells.

Role of GTP-binding proteins in the polyunsaturated fatty acid stimulated proliferation of mouse mammary epithelial cells

Polyunsaturated fatty acids enhance the proliferation of mouse mammary epithelial cells stimulated by epidermal growth factor (EGF) by modulating the post-receptor signaling pathways. The growth stimulatory effect of these fatty acids is completely inhibited by pertussis toxin, whereas the inhibition of EGF and insulin stimulated growth is only partial. The treatment of cell cultures with 12-O-tetradecanoyl-phorbol-13 acetate (TPA) reverses the growth inhibitory effect of pertussis toxin and fully restores the growth as was in the control cultures untreated with the toxin suggesting a role for PKC in this reversal. It appears that the functions of Gi-proteins are required in the mediation of fatty acid effect on growth. The predominant types of Gi alpha in mammary epithelial cells are Gi alpha 1, Gi alpha 2, and Gi alpha 3. Among these, the levels of Gi alpha 1 and 2 appears to be regulated by steroid hormones. Linoleic acid raises the level of GTP-bound Ras in the cells above the levels induced by EGF. Pertussis toxin reduces the level of Ras-GTP and inhibits phosphorylation of MAP kinase by EGF. It has been speculated that Gi-proteins interact with the receptor bound nucleotide exchange factor and the membrane anchored Raf kinase and constitute two sites for pertussis toxin action. The phosphorylation by PKC may uncouple Gi-protein interaction with these effectors and enable the agonist-induced signals to bypass the inhibitory action of PT on growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Mammary phenotypic expression induced in epidermal cells by embryonic mammary mesenchyme

The goal of this research was to establish methods for inducing mammary epithelial differentiation from nonmammary epithelium. For this purpose, mid-ventral or dorsal epidermis (skin epithelium; SKE) from 13-day rat or mouse embryos was associated with 13-day embryonic mouse mammary mesenchyme (mammary gland mesenchyme; MGM) (mouse MGM+rat or mouse SKE). The resultant MGM+SKE recombinants as well as controls (homotypic mouse mammary recombinants, homotypic mouse skin recombinants and mouse mammary mesenchyme by itself) were grafted under the renal capsule of syngeneic or athymic female nude mouse hosts. Most female hosts were induced to undergo lactogenesis by grafting an adult pituitary which elicited a state of hyperprolactinemia. Tissue recombinants of mouse MGM+rat or mouse SKE grown for 1 month in vivo formed a hair-bearing keratinized skin from which mammary ductal structures extended into the mesenchyme. The ducts were composed of columnar luminal epithelial cells as well as basal, actin-positive myoepithelial cells. When grown in pituitary-grafted hosts, the ductal epithelial cells expressed casein and alpha-lactalbumin as judged by immunocytochemistry. The expression of caseins in MGM+SKE recombinants was confirmed by Western blot. The epithelial cells in mouse MGM+rat SKE recombinants expressing milk proteins were shown to be rat cells while the surrounding connective tissue was composed of mouse cells based upon staining with Hoechst dye 33258. Using mammary-specific markers, these studies confirmed the earlier morphological studies of Propper and unequivocally demonstrated for the first time that embryonic mammary mesenchyme can induce morphological and functional mammary differentiation from nonmammary epithelium.

Analysis of the proliferative response to lysophosphatidic acid in primary cultures of mammary epithelium: differences between normal and tumor cells

The effect of lysophosphatidic acid (LPA) on the proliferation of normal and tumor mouse mammary epithelial cells in primary, serum-free, collagen gel cell culture was evaluated. LPA stimulated the growth of normal mammary epithelial cells from mature virgin mice. The growth of pregnancy-dependent tumors (PDT) was generally stimulated, although the response was attenuated in some of these tumors compared to normal cells. In contrast, the growth of 70% of ovarian-independent tumors (OIT) was inhibited by LPA; the remainder were unaffected. LPA stimulated cAMP accumulation and phosphoinositide (PI) hydrolysis in normal, PDT, and OIT. Thus, the regulation of adenylyl cyclase and PI-specific phospholipase C by LPA is similar in normal and tumor cells. Pertussis toxin (PT) partially inhibited LPA-stimulated growth in normal cells but did not affect LPA-stimulated PI hydrolysis or cAMP accumulation. Thus, PT-sensitive and -insensitive proliferative pathways are activated. PT also inhibited LPA-stimulated growth of PDT but generally had no effect on the growth of OIT. These results show that the mitogenic response to LPA is attenuated in the hormone-dependent phenotype and switches to growth inhibition in hormone-independent tumors. Furthermore, LPA stimulates multiple signal transduction pathways mediated by PT-sensitive and -insensitive G proteins. The PT-sensitive pathways are not tightly coupled to the proliferative response to LPA in tumor cells. These data suggest that alterations in G protein function may occur during tumor progression.

Omega-3 and omega-6 fatty acids and PGE2 stimulate the growth of normal but not tumor mouse mammary epithelial cells: evidence for alterations in the signaling pathways in tumor cells

The direct effect of omega-3 and omega-6 fatty acids on the proliferation of mouse mammary tumor cells (MTC) was examined in a serum-free cell culture system. While the EGF-induced proliferation of normal mammary epithelial cells was shown to be enhanced by omega-3 and omega-6 fatty acids and prostaglandins (PGs), a majority (75-80%) of primary mammary tumors were not stimulated by these agents. Compared to normal cells, some MTC cultures showed a higher susceptibility to inhibition by omega-3 fatty acids. The general lack of response of MTC cultures to PGE2 and cyclic adenosine monophosphate (cAMP) suggests some alterations in the cAMP-mediated pathway. However, the PGE2-induced cAMP levels and cAMP-dependent protein kinase (PKA) activities in the tumor cells were comparable to normal cells. We conclude that the proliferation of mammary tumor cells either follow a cAMP-PKA-independent pathway or have some alterations in the serine/threonine kinase mediated signaling pathway.