Multiple forms of p55PIK, a regulatory subunit of phosphoinositide 3-kinase, are generated by alternative initiation of translation

A cDNA encoding p55PIK, one of the regulatory subunits of phosphoinositide (phosphatidylinositol) 3-kinase, was cloned from a cDNA library derived from the mouse mammary epithelial cell line C57MG. The cDNA coding for full-length p55PIK was transiently expressed in COS-7 cells. Western blot analysis of p55PIK expression using a specific antibody against p55PIK revealed that multiple protein products with different molecular masses were detected in COS-7 cell extracts. Experiments presented here demonstrate that multiple forms of p55PIK detected in COS-7 cells were produced by alternative initiation of translation. We also show that at least two in-frame start codons (AUG#2 and AUG#5) in p55PIK mRNA are used in COS-7 cells for the initiation of translation of p55PIK into proteins of 54 kDa and 50 kDa respectively. p55PIK mRNA was also alternatively translated into two proteins in PC cells, a mouse teratoma cell line, indicating that the alternative initiation of translation of p55PIK is not restricted to COS-7 cells. Results from immunoprecipitation and Western blot analysis showed that two forms (54 kDa and 50 kDa protein species) of p55PIK were detected in C57MG cells. Interestingly, when C57MG cells were treated with insulin, only p55PIK, but not p50PIK, bound to insulin receptor substrate-1 protein, providing evidence that different forms of p55PIKs may have specific distinct roles in signal transduction pathways.

Adipose differentiation related protein (ADRP) expressed in transfected COS-7 cells selectively stimulates long chain fatty acid uptake

Adipose differentiation related protein (ADRP) is a 50-kDa novel protein cloned from a mouse 1246 adipocyte cDNA library, rapidly induced during adipocyte differentiation. We have examined ADRP function, and we show here that ADRP facilitates fatty acid uptake in COS cells transfected with ADRP cDNA. We demonstrate that uptake of long chain fatty acids was significantly stimulated in a time-dependent fashion in ADRP-expressing COS-7 cells compared with empty vector-transfected control cells. Oleic acid uptake velocity increased significantly in a dose-dependent manner in ADRP-expressing COS-7 cells compared with control cells. The transport Km was 0.051 microM, and Vmax was 57.97 pmol/10(5) cells/min in ADRP-expressing cells, and Km was 0.093 microM and Vmax was 20.13 pmol/10(5) cells/min in control cells. The oleate uptake measured at 4 degrees C was only 10% that at 37 degrees C. ADRP also stimulated uptake of palmitate and arachidonate but had no effect on uptake of medium chain fatty acid such as octanoic acid and glucose. These data suggest that ADRP specifically enhances uptake of long chain fatty acids by increasing the initial rate of uptake and provide novel information about ADRP function as a saturable transport component for long chain fatty acids.

Resveratrol, a natural product derived from grape, exhibits antiestrogenic activity and inhibits the growth of human breast cancer cells

Resveratrol is a natural phytoalexin compound found in grapes and other food products. In this study, the effect of resveratrol on the growth of human breast cancer cells was examined. Results show that resveratrol inhibits the growth of estrogen receptor(ER)-positive MCF-7 cells in a dose-dependent fashion. Detailed studies with MCF-7 cells demonstrate that resveratrol antagonized the growth-promoting effect of 17-beta-estradiol (E2) in a dose-dependent fashion at both the cellular (cell growth) and the molecular (gene activation) levels. At 5 x 10(-6) M, resveratrol abolished the growth-stimulatory effect mediated by concentrations of E2 up to 10(-9) M. The antiestrogenic effect of resveratrol could be observed at a concentration of 10(-6) M and above. The antiestrogenic effect of resveratrol was also demonstrated at the molecular level. Resveratrol in a dose-dependent fashion antagonized the stimulation by E2 of progesterone receptor gene expression in MCF-7 cells. Moreover, expression of transforming growth factor-alpha and insulin-like growth factor I receptor mRNA was inhibited while the expression of transforming growth factor beta2 mRNA was significantly elevated in MCF-7 cells cultivated in the presence of resveratrol (10(-5) M). In summary, our results show that resveratrol, a partial ER agonist itself, acts as an ER antagonist in the presence of estrogen leading to inhibition of human breast cancer cells.

Stimulation of PC cell-derived growth factor (epithelin/granulin precursor) expression by estradiol in human breast cancer cells

PC cell-derived growth factor (PCDGF) is an 88 kDa glycosylated protein isolated from a highly tumorigenic mouse teratoma derived cell line which is similar to the epithelin/granulin precursor. Using Northern blot and western blot analyses, we detect the expression of PCDGF mRNA and protein in MCF-7 human breast cancer cells. We show that 17-beta-estradiol stimulates PCDGF mRNA and protein expression in a time and dose-dependent manner. The stimulation of PCDGF expression by 17-beta-estradiol was observed as early as 4 hours and reached a maximum at 12 hours. Maximal stimulation of PCDGF mRNA and protein expression by 17-beta-estradiol was observed at a concentration of 10(-8) M. The stimulation of PCDGF expression by 17-beta-estradiol was completely inhibited by treatment with actinomycin D and with the antiestrogen 4-hydroxytamoxifen. The stimulation of PCDGF expression was also demonstrated in another human estrogen-responsive cell line T47D. The results presented here provide evidence of a novel estradiol responsive gene product in human breast cancer cell lines and give information about the hormonal control of epithelin/granulin (PCDGF) expression in these cells.

Inhibition of adipose differentiation by phosphatidylinositol 3-kinase inhibitors

Phosphatidylinositol (PI) 3-kinase plays an important role in various cellular signaling mechanisms in several cell systems. The role of PI 3-kinase in adipose differentiation was investigated. For this purpose, we examined the effect of specific inhibitors of PI 3-kinase on the differentiation of two adipogenic cell lines, 1246 and 3T3-L1. The results show that two structurally different inhibitors of PI 3-kinase, i.e., LY294002 and wortmannin, blocked adipose differentiation in a time and dose-dependent fashion. The results from time- course studies indicated that PI 3-kinase activity is most important in the early phase (day 4 to day 6) of the differentiation program. The effect of PI 3-kinase inhibitor on the expression of the peroxisome proliferator-activated receptor (PPAR) gamma, a master regulator in adipogenesis induced during the differentiation process, was also examined. LY294002 significantly inhibited the induction of PPARgamma mRNA expression. During the initiation phase of adipogenesis (day 4 to day 6), the expression of PPARgamma was induced and LY294002 blocked the increase of expression of PPARgamma mRNA. The inhibition of expression of PPARgamma may provide a molecular mechanism for the action of PI 3-kinase inhibitors on adipose differentiation.

Inhibition of tumorigenicity of the teratoma PC cell line by transfection with antisense cDNA for PC cell-derived growth factor (PCDGF, epithelin/granulin precursor)

The PC cell line is a highly tumorigenic, insulin-independent, teratoma-derived cell line isolated from the nontumorigenic, insulin-dependent 1246 cell line. Studies of the PC cell growth properties have led to the purification of an 88-kDa secreted glycoprotein called PC cell-derived growth factor (PCDGF), which has been shown to stimulate the growth of PC cells as well as 3T3 fibroblasts. Sequencing of PCDGF cDNA demonstrated its identity to the precursor of a family of 6-kDa double-cysteine-rich polypeptides called epithelins or granulins (epithelin/granulin precursor). Since PCDGF was isolated from highly tumorigenic cells, its level of expression was examined in PC cells as well as in nontumorigenic and moderately tumorigenic cells from which PC cells were derived. Northern blot and Western blot analyses indicate that the levels of PCDGF mRNA and protein were very low in the nontumorigenic cells and increased in tumorigenic cell lines in a positive correlation with their tumorigenic properties. Experiments were performed to determine whether the autocrine production of PCDGF was involved in the tumorigenicity of PC cells. For this purpose, we examined the in vivo growth properties in syngeneic C3H mice of PC cells where PCDGF expression had been inhibited by transfection of antisense PCDGF cDNA. The results show that inhibition of PCDGF expression resulted in a dramatic inhibition of tumorigenicity of the transfected cells when compared with empty-vector control cells. These data demonstrate the importance in tumor formation of overexpression of the novel growth factor PCDGF.

cDNA cloning and expression of a novel family of enzymes with calcium-independent phospholipase A2 and lysophospholipase activities

Previous studies have suggested that activation of calcium-independent PLA2 (CaIPLA2) is an early event in cell death after hypoxic injury in proximal tubule cells. An approximately 28-kD CaIPLA2 with preferential activity toward plasmalogen phospholipids has been recently purified from rabbit kidney cortex (D. Portilla and G. Dai, J Biol Chem 271, 15,451-15,457, 1996). Their report describes the cloning of a full-length rat cDNA encoding CaIPLA2, using sequences derived from the purified rabbit kidney cortex enzyme. In addition, cDNA from rabbit kidney that encode the rabbit homologue of the enzyme and a closely related isoform were isolated. The rat cDNA is predicted to encode an approximately 24-kD protein, and each cDNA contains the sequence G-F-S-Q-G, which fits the active site consensus sequence G-X-S-X-G of carboxylesterases. Several lines of evidence (DNA sequence comparison, Southern blot analysis, and examination of the expressed sequence tag database) show that CaIPLA2 enzymes are encoded by a multigene family in rats, mice, rabbits, and humans. Northern analysis of various tissues from the rat indicated that the CaIPLA2 gene is ubiquitously expressed, with highest mRNA abundance observed in the kidney and small intestine. The rat CaIPLA2 cDNA, when expressed in a baculovirus expression system, and the purified rabbit kidney cortex protein exhibit both CaIPLA2 and lysophospholipase activities. The cloned CaIPLA2 cDNA are expected to aid in understanding the role of CaIPLA2 in cell death after hypoxic/ischemic cell injury.

Identification of cell surface binding sites for PC-cell-derived growth factor, PCDGF, (epithelin/granulin precursor) on epithelial cells and fibroblasts

PC cell derived growth factor (PCDGF) is an 88-kDa glycoprotein purified from the culture medium of the highly tumorigenic mouse teratoma-derived cell line PC. PCDGF was shown to stimulate the proliferation of 3T3 fibroblasts and PC cells. Amino acid sequencing of PCDGF indicated its identity to the precursor for the 6-kDa polypeptides epithelins and granulins. In this paper, we investigated the binding of PCDGF to the mink lung epithelial cell line CCL64. Scatchard analysis indicates that 125I-PCDGF binding to CCL64 cells is curvilinear, corresponding to the existence of two classes of binding sites: high affinity binding sites (560 +/- 170 sites/cell) with a Kd1 of 43 +/- 15 pM and low affinity binding sites (16,350 +/- 5900 sites/cell) with a Kd2 of 3.9 +/- 1.9 nM. 125I-PCDGF was chemically crosslinked to cell surface receptors on CCL64 cells with disuccinimidyl suberate. A major crosslinked band of about 190 kDa with radiolabeled PCDGF was detected after SDS-PAGE, suggesting the presence of PCDGF binding sites with molecular weight of about 120 kDa. 125I. PCDGF crosslinking studies indicate the presence of PCDGF binding sites with a molecular weight similar to those of binding sites on CCL64 cells on the surface of two other PCDGF-responsive cell lines, 3T3 fibroblasts and PC cells. These data suggest that the receptors for PCDGF are widely distributed on cells of distinct embryonic origin.

Stimulation of adipose differentiation related protein (ADRP) expression by ibuprofen and indomethacin in adipocyte precursors and in adipocytes

Adipose differentiation related protein (ADRP) is a 50 kDa protein expressed at high level in differentiated adipocytes. ADRP expression is very low in undifferentiated adipocytes and increases rapidly and dramatically as the cells undergo adipose differentiation. In the present study, we demonstrate that ADRP expression at the mRNA and protein level is stimulated in adipocyte precursor cells in a time- and dose-dependent fashion by treatment with cyclooxygenase inhibitors, particularly indomethacin and ibuprofen. Lipoxygenase inhibitors such as AA861 and nordihydroguaiaretic acid were ineffective. Stimulation of ADRP expression was observed with 10(-5) M ibuprofen but maximal stimulation required a concentration of 3 x 10(-4) M. Nuclear run-on experiments indicated that indomethacin or ibuprofen stimulated the transcription of the ADRP gene in undifferentiated adipocytes. In addition to stimulating the induction of ADRP in undifferentiated cells, ibuprofen and indomethacin also stimulated the level of ADRP mRNA and protein in differentiated adipocytes. These experiments provide new information on the regulation of ADRP, an early inducible gene in the adipocyte differentiation programme in adipocyte precursors and in adipocytes and identify a new target for cyclooxygenase inhibitor action during adipocyte differentiation.

Adipose differentiation-related protein is an ubiquitously expressed lipid storage droplet-associated protein

The adipose differentiation-related protein (ADRP) was first characterized as a mRNA induced early during adipocyte differentiation (Jiang, H. P., and G. Serrero. 1992. Proc. Natl. Acad. Sci. USA. 89:7856-7860). The present study demonstrates that ADRP mRNA is expressed in a variety of tissues and cultured cell lines. Immunocytochemical examination revealed that ADRP localizes to neutral lipid storage droplets in cultured murine 3T3-L1 adipocytes, murine MA-10 Leydig cells, Chinese hamster ovary (CHO) fibroblasts, and human HepG2 hepatoma cells; the association of ADRP with lipid droplets was confirmed by subcellular fractionation of MA-10 Leydig cells. In addition to ADRP, steroidogenic cells and adipocytes express the perilipins, a family of lipid droplet-associated proteins that share a highly related sequence domain with ADRP. ADRP and perilipins co-localize on lipid droplets in MA-10 Leydig cells. While ADRP was found on small lipid droplets in 3T3-L1 preadipocytes and early differentiated adipocytes, it was absent in maturing adipocytes. In contrast, perilipins were absent early during differentiation, but were found on small and large lipid droplets at later stages. The transition in surface protein composition of adipocyte lipid droplets from ADRP to perilipins occurred 3 days after the initiation of differentiation when cells displayed co-localizatioin of both proteins on the same lipid droplets. The specific localization of adipose differentiation-related protein to lipid droplets in a wide variety of cells suggests that ADRP plays a role in management of neutral lipid stores.

Prostaglandin F2alpha receptor (FP receptor) agonists are potent adipose differentiation inhibitors for primary culture of adipocyte precursors in defined medium

Prostaglandin F2alpha inhibits adipose differentiation of primary culture of adipocyte precursors and of the adipogenic cell line 1246 in defined medium. In the present paper, we investigated the effect of FP receptor agonists cloprostenol and fluprostenol on the differentiation of newborn rat adipocyte precursors in primary culture. The results show that cloprostenol and fluprostenol are very potent inhibitors of adipose differentiation. Dose response studies indicate that both agonists are more potent than PGF2alpha in inhibiting adipocyte precursors differentiation. 50% inhibition of adipose differentiation was observed at a concentration of 3 x 10(-12) M for cloprostenol and 3 to 10 x 10(-11) M for fluprostenol respectively whereas the PGF2alpha concentration required to elicit the same effect was 10(-8) M. In contrast compounds structurally related to PGE2 such as 17-phenyl trinor PGE2 had no effect on adipose differentiation except when added at a 10,000-fold higher concentration.

Endocrine and paracrine negative regulators of adipose differentiation

Obesity which is characterized by an abnormal adipose tissue development is a first degree public health hazard in industrialized countries. One important aspect in the study of adipose tissue development is to investigate the hormonal control of proliferation and differentiation. Any qualitative or quantitative change in these hormones or their receptors can result in abnormalities in the process of proliferation and/or differentiation possibly leading to obesity. Therefore, it is important to identify these factors and investigate their mechanism of action. We have concentrated our efforts in the study of factors triggering differentiation (positive regulators) and also of factors inhibiting differentiation (negative regulators). The present paper provides evidence of the importance of EGF/TGF-alpha and of PGF2 alpha as differentiation inhibitors for adipocyte precursors in primary culture. Data presented here also demonstrate that TGF-alpha is expressed in adipose tissue and that its expression is specifically stimulated by PGF2 alpha, thus suggesting the existence of an amplification mechanism between two differentiation inhibitors within the adipose tissue. The importance of these two types of differentiation inhibitors in the regulation of adipose tissue development is discussed.

Prostaglandin F2 alpha stimulates transforming growth factor-alpha expression in adipocyte precursors

Transforming growth factor-alpha (TGF alpha) and prostaglandin F2 alpha (PGF2 alpha) are potent inhibitors of adipocyte differentiation. We demonstrate here that TGF alpha messenger RNA (mRNA) is expressed in freshly isolated fat pads and in primary culture of adipocyte precursors cultivated in defined medium before and after differentiation. We show that PGF2 alpha stimulated TGF alpha mRNA expression in a dose-dependent manner. PGF2 alpha also stimulated TGF alpha production in the culture medium of adipocyte precursors in primary culture. PGF2 alpha stimulated TGF alpha mRNA expression in both undifferentiated and differentiated cells. 9 alpha,11 beta-PGF2 alpha, which also inhibited adipose differentiation, stimulated TGF alpha mRNA expression similarly to PGF2 alpha, whereas other PGs had no effect on TGF alpha mRNA expression. The time-course experiment indicates that the stimulation of TGF alpha mRNA expression by PGF2 alpha is observed within 6 h of exposure to PGF2 alpha and is inhibited by treatment of the cells with actinomycin D. The effect of PGF2 alpha on TGF alpha expression did not require activation of protein kinase C and was fully reversible. As both TGF alpha and PGF2 alpha are inhibitors of adipose differentiation, it is suggested that stimulation of TGF alpha expression by PGF2 alpha could represent an amplification mechanism to modulate adipocyte precursor differentiation and adipocyte function within the adipose tissue.

Prostaglandin F2 alpha inhibits epidermal growth factor binding to cellular receptors on adipocyte precursors in primary culture

Prostaglandin F2 alpha (PGF2 alpha) and epidermal growth factor (EGF) are potent differentiation inhibitors of adipocyte precursors in primary culture. We show here that PGF2 alpha specifically inhibited EGF binding to adipocyte precursors in a dose dependent fashion. Scatchard analysis indicates that PGF2 alpha causes a 50% decrease in the number of available EGF cell surface receptors without change in receptor affinity. Comparison of EGF binding at different temperatures and on fixed cells indicates that PGF2 alpha increases internalization of EGF-receptor complexes in adipocyte precursors. Phorbol myristate acetate (PMA) also inhibited EGF binding in adipocyte precursors. PGF2 alpha effect was abolished in cells exposed to prolonged treatment with PMA indicating that PGF2 alpha effect on EGF binding is mediated by protein kinase C. These results would suggest that in adipocyte precursors PGF2 alpha may be the physiological mediator of phorbol ester effect on EGF receptor properties.

Characterization of calcium-independent cytosolic phospholipase A2 activity in the submucosal regions of rat stomach and small intestine

This study was undertaken to compare the calcium-independent phospholipase A2 (PLA2) activities in the cytosols of twelve rat tissues and to determine whether their activities were distinct. 1-O-Alk-1'-enyl-2-[14C]-oleoyl-sn-glycero-3-phosphocholine (PlsC) and 1-O-Alk-1'-enyl-2-[14C]oleoyl-sn-glycero-3-phosphoethanolamine (PlsE) were synthesized and used as substrates, instead of phosphatidyl compounds, to exclude hydrolysis by cytosolic PLA1 activity that could be present in some of the cytosolic preparations. For each tissue, we examined substrate specificity, pH optimum, and effect of adenosine triphosphate (ATP) and ATP analogues. PLA2 activity was detected in eleven out of the twelve issues examined. Based on substrate specificity and pH optimum, cytosolic calcium-independent PLA2 were classified in three groups. The first group, which included PLA2 from small intestine, stomach and spleen, had the highest specific activity with PlsC as substrate (1253, 309 and 75 nmol/mg protein/hour, respectively) and an optimal pH at 6.5. Activity with PlsE as substrate was much lower (20-37%) than with PlsC. The second group of PLA2 activities included the cytosolic activities from thymus, lung, liver and pancreas that showed lower specific activities for both substrates (14-23 nmol/mg protein/hour with PlsC) and had a broader optimal pH range of 6.1 to 7.5. The cytosols from brain, kidney, heart and muscle comprised the third PLA2 group that was found to have a higher specific activity with PlsE (5-20 nmol/mg protein/hour) than PlsC and an optimal pH range from 7.4 to 7.9.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of adipose differentiation by 9 alpha, 11 beta-prostaglandin F2 alpha

Prostaglandin F2 alpha (PGF2 alpha) is a potent adipose differentiation inhibitor for the adipogenic cell line 1246 and for adipocyte precursors in primary culture with an ED50 of 3 x 10(-8) M. In this paper, we examined the effect of several prostaglandins which have structural similarities with PGF2 alpha on the differentiation of 1246 cells and of adipocyte precursors in primary culture. The results show that only 9 alpha,11 beta-PGF2 alpha is as potent as PGF2 alpha to inhibit differentiation of adipocyte precursors in primary culture and of the adipogenic cell line 1246. In the presence of 9 alpha,11 beta-PGF2 alpha, the cells remained fibroblast-like, typical of undifferentiated adipocyte precursors. Triglyceride accumulation and increase of specific activity for glycerol-3-phosphate dehydrogenase were inhibited. In addition, mRNA expression of early markers of differentiation such as lipoprotein lipase (LPL) and fatty acid binding protein (FAB) was decreased. The isomer 9 beta,11 alpha-PGF2 alpha and other PGF2 alpha derivatives were inactive. These results provide new information on the biological activity of 9 alpha,11 beta-PGF2 alpha as an inhibitor of adipose differentiation and about the structural characteristics of prostaglandins required for maintenance of a high adipose differentiation inhibitory effect.

A novel mouse gene highly conserved throughout evolution: regulation in adipocyte differentiation and in tumorigenic cell lines

A cDNA clone referred to as 168 was previously isolated from mouse 1246 adipocytes by differential hybridization on the basis of its down regulation in adipocytes when compared to preadipocytes. 5' RACE was used to obtain a full length clone of 761 bp encoding for a highly basic 25 kD polypeptide that is extremely conserved in several diverse species of eukaryotes. There is a single amino acid substitution at position 202 compared to the human homolog, QM, a putative tumor suppressor. Clone 168 mRNA decreases 80% in rat primary culture of adipocytes compared to preadipocytes and does not decrease when differentiation is blocked by PGF2 alpha or EGF, indicating that the decrease is correlated with expression of the differentiation phenotype. Finally, two 1246 cell line variants that exhibit altered growth and increased tumorigenicity have a similar level of 168 mRNA when compared to the non tumorigenic adipogenic parent cell line.

Structure of the gene encoding mouse adipose differentiation-related protein (ADRP)

Adipose differentiation-related protein (ADRP) is a novel 50-kDa membrane-associated protein whose message levels are induced rapidly and maximally after triggering adipocyte differentiation. The gene encoding mouse ADRP has been isolated and characterized from four overlapping lambda phage clones. The gene spans 14 kb and contains 8 exons and 7 introns. Exons range in size from 50 to 696 bp and intron sizes range from 87 bp to 4.3 kb. Major and minor transcription initiation sites were determined 76 and 78 bp, respectively, upstream of the initiator methionine. A TATTTTA sequence is centered 30 bp upstream of the major transcription start site, and within the 5'-flanking region there are several putative transcription factor binding sites. ADRP has been mapped to chromosome 4, specifically between the b and Ifa loci. A second ADRP-like gene was isolated and partially characterized. This second locus is not expressed in 12 different mouse tissues and shares 87% sequence similarity to ADRP over exon and intron regions analyzed. Finally, this is the first reported genomic structure of ADRP.

Purification of an autocrine growth factor homologous with mouse epithelin precursor from a highly tumorigenic cell line

PC cell line is a highly tumorigenic insulin-independent variant from the teratoma-derived adipogenic cell line 1246. Culture medium of PC cells contains a growth promoting activity for 3T3 cells and producer cells. PC cell-derived growth factor (PCDGF) was purified to homogeneity from PC cell-conditioned medium as an apparent 88-kDa protein by chromatography on heparin-Sepharose, Sephacryl S-200, and phenyl-Sepharose. Digestion with peptide-N-glycosidase F yielded an apparent 68-kDa protein component indicating that PCDGF is a glycoprotein containing about 20 kDa of carbohydrate. Partial sequence from Edman degradation of peptide fragments obtained by digestion of PCDGF with cyanogen bromide and trypsin demonstrates that PCDGF contains regions of sequence identity to that deduced from the granulin or epithelin precursor cDNAs. Granulins are small polypeptides purified from granulocyte extracts with no apparent biological functions. Epithelins are cell growth modulators purified as small molecular mass 6-kDa polypeptides from kidney extracts. The existence of a large molecular mass precursor for granulin or epithelin has been predicted based upon recently cloned cDNAs encoding these biomolecules within a 63.5-kDa protein with putative glycosylation sites. No biological activity has previously been attributed to the precursor. The present results indicate that PCDGF is a potential precursor for epithelin and/or granulin, that this 88-kDa protein is secreted and glycosylated, and that it can function as a mitogen for 3T3 cells as well as an autocrine growth factor for PC cells.

Impaired epidermal growth factor production in genetically obese ob/ob mice

Epidermal growth factor (EGF) is a potent inhibitor of adipose differentiation in vitro and delays adipose tissue development in vivo. Here we show that in the homozygous male obese mice the level of EGF in the submaxillary gland and plasma is significantly lower than in the glands and plasma of age-matched control littermates. This EGF deficiency in ob/ob mice was observed as early as 5 wk of age when obesity had just become apparent and was also found in adult mice. The level of prepro-EGF mRNA expression in the submaxillary gland was also lower in obese mice than in control littermates. However, the level of kidney prepro-EGF mRNA was the same in mice with both phenotypes, suggesting that the regulation of prepro-EGF mRNA expression is different in both tissues. These results indicate that genetic obesity in mice is accompanied by a decrease in the production of EGF.

Nucleotide sequence of the C-terminal region of the mouse epidermal growth factor receptor and expression in teratoma-derived cell lines with increased tumorigenic properties

The isolation of a cDNA corresponding to a portion (amino acid 943 to 1073) of the cytoplasmic domain of the mouse EGF receptor surrounding the auto phosphorylation sites was obtained by using the reverse transcriptase polymerase chain reaction (RT-PCR) approach. Deduced amino acid sequence of mouse EGF receptor (EGFr) shows a 92% and 76% homology to corresponding regions in the human and the chicken EGFr, respectively. This cDNA was used to develop a sensitive RNase protection assay to investigate EGF receptor mRNA expression in mouse C3H teratoma derived cell lines with increased tumorigenic properties which display a progressive decrease of EGF binding and response. The results show that increased tumorigenicity was not accompanied by a change in EGF receptor mRNA expression. Moreover, they indicate that the RNase protection assay developed using the probe described here is a sensitive approach to investigate EGF receptor expression in murine cells.

Fibroblast growth factor inhibits proliferation of a highly tumorigenic insulin-independent teratoma-derived cell line

The present paper examines the effect of basic fibroblast growth factor (bFGF) on the proliferation of teratoma-derived cell lines having increased tumorigenic properties isolated from the non-tumorigenic adipogenic cell line 1246. Although FGF is a mitogen for the non tumorigenic 1246 cells and for the moderately tumorigenic 1246-3A cells derived from the 1246 cells, bFGF inhibits the proliferation and DNA synthesis of the highly tumorigenic PC cells starting at concentration as low as 30 pg/ml. The inhibitory effect of FGF on PC cell growth is irreversible as demonstrated by the inability of the cells to resume proliferation once FGF is removed from the culture medium. Comparison of 125I-bFGF binding to the three cell lines was performed. Based on the Scatchard analysis of the binding data, PC cells display only low affinity class of FGF binding sites whereas 1246 and 1246-3A cells presented also high affinity binding sites. The inhibitory effect of FGF on PC cells did not go through activation of a PKC mediated pathway, which is also known to inhibit PC cell proliferation, since FGF inhibition of PC cell growth was still apparent after PKC down regulation. FGF was still able to transiently stimulate the expression of mRNA for early growth associated genes as demonstrated by c-myc and c-fos expression, although it inhibited cell proliferation on PC cells. Our data demonstrate that the highly tumorigenic teratoma cells acquire an inhibitory response for a factor which is growth stimulatory to non-tumorigenic and moderately tumorigenic cells from which they are derived.

Paracrine regulation of adipose differentiation by arachidonate metabolites: prostaglandin F2 alpha inhibits early and late markers of differentiation in the adipogenic cell line 1246

The effect of arachidonate metabolites on the differentiation of the adipogenic cell line 1246 was investigated. Among the metabolites examined, only prostaglandin F2 alpha (PGF2 alpha) inhibited differentiation in a dose-dependent fashion with an ED50 of 3 x 10(-9) M. PGF2 alpha inhibited the mRNA expression of lipoprotein lipase, clone 154, and fatty acid-binding protein, which are early markers of differentiation, as well as glycerol-3-phosphate dehydrogenase specific activity and triglyceride accumulation, which are late markers of differentiation. Chronic exposure of 1246 cells to PGF2 alpha before and during differentiation indicated that the cells that have just initiated their differentiation program were the most susceptible to the inhibitory effect of PGF2 alpha. Since 1246 cells produce PGs, we determined whether the PG produced by the cells influenced adipose differentiation. Cyclooxygenase inhibitors added to the culture medium stimulated differentiation of 1246 cells up to 18-fold depending on the type and concentration of inhibitor used. In contrast, lipoxygenase inhibitors had no effect. Treatment of 1246 cells with arachidonic acid resulted in a dose-dependent inhibition of cell differentiation. Oleate or linoleate had no effect. These data indicate that PGF2 alpha inhibits early and late events of adipose differentiation and that the endogenous production of PGs (particularly PGF2 alpha) plays an important role as a negative paracrine or autocrine regulatory pathway of adipose differentiation.