Nuclear accumulation of epidermal growth factor in cultured bovine corneal endothelial and granulosa cells

Epidermal growth factor: uptake and fate

Lateral diffusion of epidermal growth factor (EGF) receptors along the plane of the cell membrane can be measured using fluorescently labelled analogues of EGF and the fluorescence photobleaching recovery method in cultured cells. With the aid of high image-intensified fluorescent microscopy, the receptors, which are initially distributed diffusely, form patches and undergo endocytosis at 37 degrees C. These gross processes may not be critical in mediating the initial, rapid actions of the hormone. The processes of uptake and endocytosis correspond biochemically to the loss of surface receptors ('down-regulation') and degradation of the receptor and hormone via lysosomes. The EGF receptors are not apparently recycled or re-utilized, and they are continuously internalized, even in the absence of ligand. Since all manoeuvres that interfere with intracellular degradation or processing block mitogenesis, it is proposed that one or both of these may be essential processes, although in such a case they must be continuous and protracted functions. Slow nuclear accumulation of the complex of hormone and receptor may be an important process. In addition, evidence suggests that limited (submicroscopic) receptor aggregation (dimerization) at the cell surface may be necessary and sufficient to trigger the long-term effects (but not the immediate effects), and thus this aggregation may be required for endocytosis. The ligand itself may not be an essential structural component of the action of the receptor since anti-receptor antibodies can elicit mitogenic responses. Recent results suggest that EGF receptors normally exist in a low affinity state which is rapidly converted by EGF (at 37 degrees C but not at 4 degrees C) to a high affinity state by a process that requires prior intact protein synthesis. Furthermore, the accumulation of a special, stable intracellular pool of the complex may be related to the control of cellular growth (and tumour promotion).

Targeted disruption of Col8a1 and Col8a2 genes in mice leads to anterior segment abnormalities in the eye

Collagen VIII is localized in subendothelial and subepithelial extracellular matrices. It is a major component of Descemet's membrane, a thick basement membrane under the corneal endothelium, where it forms a hexagonal lattice structure; a similar structure, albeit less extensive, may be formed in other basement membranes. We have examined the function of collagen VIII in mice by targeted inactivation of the genes encoding the two polypeptide subunits, Col8a1 and Col8a2. Analysis of these mice reveals no major structural defects in most organs, but demonstrates that type VIII collagen is required for normal anterior eye development, particularly the formation of a corneal stroma with the appropriate number of fibroblastic cell layers and Descemet's membrane of appropriate thickness. Complete lack of type VIII collagen leads to dysgenesis of the anterior segment of the eye: a globoid, keratoglobus-like protrusion of the anterior chamber with a thin corneal stroma. Descemet's membrane is markedly thinned. The corneal endothelial cells are enlarged and reduced in number, and show a decreased ability to proliferate in response to different growth factors in vitro. An important function of collagen VIII may therefore be to generate a peri- or subcellular matrix environment that permits or stimulates cell proliferation.

Nuclear localisation of endogenous SUMO-1-modified PDGF-C in human thyroid tissue and cell lines

We investigated post-translational modification and subcellular localisation of endogenous platelet-derived growth factor-C (PDGF-C) in human thyroid papillary carcinomas (PTC), non-neoplastic thyroid tissues, and a selection of cultured cell lines. PDGF-C expressed nuclear localisation in 95% of all tested cell types in culture and in 10% of the thyrocytes from both PTC and non-neoplastic tissue. The cell lines expressed two forms of full-length PDGF-C, approximately 39 and approximately 55 kDa, in cell membrane and cytosol, while the approximately 55 kDa form dominated in the nucleus where it was partly chromatin-associated. The approximately 55 kDa form was post-translationally modified by SUMO-1. The putative PDGF-C SUMOylation site is the surface exposed (314)lysine part of a positively charged loop ((312)RPKTGVRGLHK(322)) with characteristics of a nuclear localisation signal. The tissue thyrocytes expressed a non-SUMOylated approximately 43 kDa and the 55 kDa PDGF-C. The SUMO-1 modified approximately 55 kDa PDGF-C expression was low in PTC where the approximately 43 kDa PDGF-C dominated. This is in contrast to non-neoplastic tissue and cultured cells where the SUMOylated approximately 55 kDa PDGF-C was strongly expressed. Our data provide novel evidence for nuclear localisation of PDGF-C, post-translational modification by SUMOylation and the expression of a novel form of PDGF-C in human papillary thyroid carcinomas.

Immunohistochemical localization of transforming growth factor alpha in regenerating rat liver

Immunohistochemical localization of TGF-alpha and cell proliferation kinetics during liver regeneration after two-thirds partial hepatectomy (PH) were investigated. Twenty-four to 72 hr after PH, appreciable increase in the number of TGF-alpha-positive hepatocytes was observed in zones 1 and 2. At the peak at 36 hr, almost all positive cells were stained in their nuclei. Considerable increase in the BrdU labeling index was observed 24-36 hr after PH with a peak at 24 hr in zones 1 and 2. These results indicated an association between TGF-alpha expression and hepatocyte regeneration. It is suggested that immunohistochemical localization of TGF-alpha may be a useful marker of cell proliferation activity in rat liver.

Expression of Ciliary Neurotrophic Factor and the Neurotrophins-Nerve Growth Factor, Brain-Derived Neurotrophic Factor and Neurotrophin 3-in Cultured Rat Hippocampal Astrocytes

Cultured astrocytes are known to possess a range of neurotrophic activities in culture. In order to examine which factors may be responsible for these activities, we have examined the expression of the genes for four known neurotrophic factors-ciliary neurotrophic factor (CNTF), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3)-in purified astrocyte cultures derived from neonatal rat hippocampus. Hippocampal astrocytes were found to express mRNA for three neurotrophic factors-CNTF, NGF and NT3-at significantly higher levels than other cultured cell types or cell lines examined. BDNF messenger RNA (mRNA), however, was undetectable in these astrocytes. The levels of CNTF, NGF and NT3 mRNA in astrocytes were largely unaffected by their degree of confluency, while serum removal caused only a transient decrease in mRNA levels, which returned to basal levels within 48 h. Astrocyte-derived CNTF was found to comigrate with recombinant rat CNTF at 23 kD on a Western blot. Immunocytochemical analysis revealed strong CNTF immunoreactivity in the cytoplasm of astrocytes, weak staining in the nucleus, but no CNTF at the cell surface. NGF and NT3 were undetectable immunocytochemically. CNTF-like activity, as assessed by bioassay on ciliary ganglion neurons, was found in the extract of cultured astrocytes but not in conditioned medium, whereas astrocyte-conditioned medium supported survival of dorsal root ganglion neurons but not ciliary or nodose ganglion neurons. This conditioned medium activity was neutralized with antibodies to NGF. Astrocyte extract also supported survival of dorsal root ganglion and nodose ganglion neurons, but these activities were not blocked by anti-NGF. Part, but not all, of the activity in astrocyte extracts which sustained nodose ganglion neurons could be attributed to CNTF.

Greater expression of transforming growth factor alpha and proliferating cell nuclear antigen staining in mouse hepatoblastomas than hepatocellular carcinomas induced by a diethylnitrosamine-sodium phenobarbital regimen

Transforming growth factor alpha (TGF-alpha) is a potent stimulator of normal hepatocyte proliferation, considered to have relationship to the liver regeneration or carcinogenesis. In this study, we investigated immunohistochemically the association between expression of TGF-alpha and cell proliferation activity in mouse hepatoblastomas (HBs) and hepatocellular carcinomas (HCCs) induced in B6C3F1 mice by diethylnitrosamine and sodium phenobarbital. The TGF-alpha-positive rate in HBs (29.2%) was significantly higher than that in HCCs (12.7%). Likewise, the proliferating cell nuclear antigen-positive rate (22.2%) was higher than the HCC value (14.5%). On the individual data for both TGF-alpha and PCNA, most of the HBs showed higher positive rates than HCCs. In HBs, TGF-alpha was localized only in the nuclei, whereas some HCC cells stained positive both in their nuclei and cytoplasm (0.6%). These results suggest expression of TGF-alpha and its localization might be linked to cell proliferation and play a role in malignant progression of mouse HBs.

Immunohistochemical localization of activated EGF receptor in human eccrine and apocrine sweat glands

Epidermal growth factor (EGF) is secreted into sweat from secretory cells of human sweat glands. The function of EGF in sweat is poorly understood. The biological function of EGF is exerted by the binding of EGF to the receptor (EGFR) and its activation. Therefore, we immunohistochemically localized the activated form of EGFR in human eccrine and apocrine sweat glands to assess the functional importance of the EGF-EGFR system in human sweat glands. Frozen sections of human skin were stained with a monoclonal antibody (MAb) specific for tyrosine-phosphorylated (activated) EGFR and with an MAb that stains both activated and non-activated EGFR. In the secretory portion of eccrine sweat glands, nuclei of the secretory cells were stained with the anti-activated EGFR MAb. In coiled and straight portions of eccrine sweat ducts, nuclei of luminal and peripheral cells were stained with the antibody specific for activated EGFR. Luminal cell membranes and luminal cytoplasm of inner ductal cells possessed non-activated EGFR. In the secretory portion of apocrine sweat glands, activated EGFRs were present in cytoplasm and nuclei of secretory cells. These data suggest that EGF, already known to be present in the cytoplasm of secretory cells in eccrine and apocrine sweat glands, activates EGFR in the nuclei of secretory cells themselves in an intracrine manner. Because ductal cells do not express EGF, EGF in the sweat secreted from the secretory cells should activate EGFR in the ductal cells in a paracrine manner. (J Histochem Cytochem 49:597-601, 2001)

Immunohistochemical localization of transforming growth factor alpha in chemically induced rat hepatocellular carcinomas with reference to differentiation and proliferation

Hepatocellular carcinomas (HCCs) were induced in male Fischer 344 rats with dietary 3'-methyl-4-(dimethylamino)-azobenzene treatment and were classified into solid, glandular (well- or poorly differentiated), and trabecular types. Investigation of cell proliferation kinetics and immunohistochemical localization of transforming growth factor alpha (TGF-alpha) demonstrated all solid (n = 24) and poorly differentiated glandular type (n = 6) HCCs to have TGF-alpha-positive nuclei. Nuclear staining of TGF-alpha was also observed in 13 of 28 (46%) trabecular-type HCCs, whereas 12 (43%) exhibited cytoplasmic staining, and 3 (11%) were negative. As for well-differentiated glandular HCCs, 7 of 20 (35%) were positively stained in their nucleus, another 7 (35%) demonstrated antibody binding in the cytoplasm, and 6 (30%) were negative. The order for growth rate evaluated by bromodeoxyuridine (BrdU) labeling was solid (38.22%), poorly differentiated glandular (26.82%), trabecular (7.98%), and well-differentiated glandular (2.57%) types. For trabecular HCCs with nuclear, cytoplasmic, or negative TGF reactions, values were 13.39% (n = 13), 3.61% (n = 12), and 2.01% (n = 3), respectively. Likewise, BrdU-labeling indices for the counterpart groups of well-differentiated glandular type HCCs were 4.53, 1.91, and 1.29%, respectively. The results indicate that TGF-alpha expression might be linked to histopathological differentiation and cell proliferation in rat HCCs.

Fibroblast growth factors are translocated to the nucleus of human endothelial cells in a microtubule- and lysosome-independent pathway

Exogenous acidic and basic fibroblast growth factors undergo rapid nuclear translocation in human umbilical vein endothelial cells. When nuclear translocation reaches saturation, more than 70% of the internalized growth factors are in the nuclear fraction. Lysosomal inhibitors, such as leupeptin and chloroquine, and microtubule inhibitors including colchicine and 2-methoxyl-beta-estradiol neither increase nor decrease nuclear translocation. The results suggest that nuclear translocation of fibroblast growth factors does not require cytosolic accumulation or lysosomal processing and that the transportation of exogenous growth factors across the cytoplasm is independent of microtubules.

Prepubertal genistein treatment modulates TGF-alpha, EGF and EGF-receptor mRNAs and proteins in the rat mammary gland

We have previously demonstrated that exposure to genistein early in life protects against chemically-induced mammary cancer in rats. To gain insight into the mechanism of action, we have investigated the expression of the EGF-signaling pathway in the mammary glands of 21 and 50 day old rats treated on days 16, 18, and 20 postpartum with 500 microg genistein/g body weight (B.W.) or an equivalent volume of the vehicle, dimethylsulfoxide (DMSO). This prepubertal genistein treatment up-regulated TGF-alpha and the EGF-receptor (EGFR), but not EGF, in mammary terminal ductal structures at day 21 postpartum. TGF-alpha, EGF and EGFR mRNA levels were similar in 21 day old control- and genistein-treated animals. At day 50 postpartum, mammary glands of genistein treated rats had more lobules and fewer terminal end buds (TEBs) and terminal ducts (TDs), i.e. they were more differentiated. TGF-alpha mRNA levels were down-regulated in TEB of proestrous and estrous females; EGF mRNA levels were down-regulated in TDs of proestrous, but not in estrous females; and EGFR mRNA levels were not altered in 50 day old proestrous or estrous female rats. EGFR immunostaining intensity was decreased in TEBs, but not in the total gland. EGF was increased in TEBs and TDs. TGF-alpha, EGF and EGFR were also observed in the stroma and fat pad, but genistein treatment did not alter the expression of these proteins in those locations. TGF-alpha, but not EGF and EGFR, immunostaining was observed in cell nuclei (not modulated by genistein), suggesting that this growth factor may act directly on nuclear events such as transcription and DNA replication. For comparative purposes, prepubertal diethylstilbestrol treatment was investigated and found to decrease EGFR immunostaining intensity and total IHC staining in all terminal ductal structures. We conclude that prepubertal genistein treatment directly stimulates TGF-alpha and EGFR to enhance mammary gland differentiation. This programs the differentiated cells for a down-regulated EGF-signaling pathway in TEBs and TDs of adult mammary glands. Reduced EGFR expression at time of carcinogen exposure may account for genistein programming against mammary cancer.

Nuclear translocation of human angiogenin in cultured human umbilical artery endothelial cells is microtubule and lysosome independent

Exogenous angiogenin undergoes rapid nuclear translocation in cultured human umbilical artery endothelial cells at 37 degrees C but not at 4 degrees C. Treatment of cells with colchicine, nocodazole and taxol, which disrupt the microtubule system, does not affect the nuclear translocation process of angiogenin, suggesting that cells transport internalized angiogenin in a microtubule independent fashion. Lysosomal inhibitors, chloroquine and leupeptin, neither inhibit nor enhance the nuclear translocation of angiogenin, indicating that lysosomal targeting and processing are not required for, and do not compete with, the nuclear translocation. Moreover, treatment of cells with a tyrosine kinase antagonist, genistein, does not change the ability of the cells to translocate angiogenin into the nucleus. We suggest that exogenous angiogenin is translocated to the nucleus by a mechanism that does not require activation of tyrosine kinase, but includes receptor-mediated endocytosis, microtubule and lysosome independent transport across the cytoplasm, and nuclear localization sequence-assisted nuclear import.

Internalization of prolactin receptor and prolactin in transfected cells does not involve nuclear translocation

Prolactin (PRL) interacts with a specific, well characterized plasma membrane receptor (PRLR) that is coupled to signal transduction pathways involving Jak2, Fyn, and MAP kinases, and signal transducers and activators of transcription (STAT). Although a few previous studies have indicated nuclear translocation of PRL in IL-2 stimulated T lymphocytes, PRL-dependent Nb2 lymphoma cell lines and 235–1 lactotrophs, the mechanisms of nuclear targeting remain unknown and conflicting results have been reported concerning the putative nuclear translocation of the PRLR. We therefore decided to investigate nuclear translocation of PRLR and PRL in various cell lines transfected with an expression plasmid encoding PRLR, using confocal laser microscopy. We have constructed various cDNAs of the long and short forms of the rat PRLR containing an oligonucleotide encoding a Flag epitope inserted either just before the N-terminal amino acid or in the C-terminal end of the mature receptor (named N-terminal or C-terminal Flag-tagged PRLR). The corresponding receptors function as the PRLR in transfected cells: they are expressed at the plasma membrane and in compartments of the secretory pathway, they bind PRL with normal affinity (Kd= 4x10(−10) M) and have the same capacity to stimulate the transcriptional activity of a milk protein (beta-casein) gene as wild-type PRLR. In addition, the tagged receptors are much more efficiently immunodetected using anti-Flag antibodies, as compared to anti-PRL antibodies (U5 or U6). Immunofluorescence combined with detailed confocal laser microscopy showed that addition of PRL (0 to 12 hours) to COS-7, CHO and NIH-3T3 transfected fibroblasts induces rapid internalization of the receptor (long form), without any translocation to the nucleus. Using PRL-R tagged both in the N-terminal or C-terminal regions of the mature receptor excludes the possibility of a cleaved fragment which could have been subsequently imported into the nucleus. An absence of nuclear translocation of PRLR was also observed in a 293 cell line stably expressing the receptor, and in physiological targets for PRL, i.e. in Nb2 lymphoma cells expressing the Nb2 form of the receptor or in BGME mammary gland epithelial cells upon overexpression of a Flag-tagged PRLR. Similarly, the short form of the PRLR was not detected in nuclei of transfected COS cells upon PRL treatment. Clearly, our results provide evidence that internalization of the plasma membrane PRLR does not lead to nuclear translocation of the receptor, or part of it, in most fibroblasts and epithelial cells at physiological concentrations of PRL. Also, in co-localization experiments, PRL was internalized without nuclear translocation. Activation of STATs transcription factors and MAP kinases, as well as translocation of these proteins to the nucleus following their phosphorylation, probably remains the intracellular mechanism coupling stimulation to nuclear events.

In vitro evaluation of iodine-125-labeled monoclonal antibody (MAb 425) in human high-grade glioma cells

Human high-grade glioma cell lines (A1207, U-87MG, U-373MG, and F39) with high levels of epidermal growth factor receptor (EGF-R) expression were incubated for 2-48 h with 1 microCi/ml of the EGF-R-specific 125I-MAb 425 and measured for surface-bound, cytoplasmic, and nuclear radioactivity. The A1207 and U-373MG cell lines showed the highest surface-bound radioactivity with 215.9 +/- 8.7 nCi (30 h) and 287.8 +/- 23.2 nCi (24 h)/10(6) cells, respectively, whereas the U-87MG and the F39 cell lines bound significantly less antibody (48.8 +/- 5.4 nCi [48 h] and 31.1 +/- 0.7 nCi [24 h]). Surface-bound antibody was efficiently internalized into the cytoplasm. The U-373MG, U-87MG, and A1207 cell lines achieved 19.8% +/- 2.1 internalization of the surface-bound antibody in contrast to > 40% for the F39 cell line. Only the A1207 cell line showed significant nuclear radioactivity. There was no correlation between the reported EGF-R number and amount of antibody bound or internalized. We conclude that binding and uptake of the 125I-MAb 425 is specific for human glioma cells and shows saturation kinetics independent of receptor density.

Identification of phenylalanine 346 in the rat growth hormone receptor as being critical for ligand-mediated internalization and down-regulation

The functional significance of growth hormone (GH) receptor (GHR) internalization is unknown; therefore, we have analyzed domains and individual amino acids in the cytoplasmic region of the rat GHR required for ligand-mediated receptor internalization, receptor down-regulation, and transcriptional signaling. When various mutated GHR cDNAs were transfected stably into Chinese hamster ovary cells or transiently into monkey kidney (COS-7) cells, internalization of the GHR was found to be dependent upon a domain located between amino acids 318 and 380. Mutational analysis of aromatic residues in this domain revealed that phenylalanine 346 is required for internalization. Receptor down-regulation in transiently transfected COS-7 cells was also dependent upon the phenylalanine 346 residue of the GHR, since no GH-induced down-regulation was observed in cells expressing the F346A GHR mutant. In contrast, the ability to stimulate transcription of the serine protease inhibitor 2.1 promoter by the GHR was not affected by the phenylalanine 346 to alanine mutation. These results demonstrate that phenylalanine 346 is essential for GHR internalization and down-regulation but not for transcriptional signaling, suggesting that ligand-mediated endocytosis is not a prerequisite for GH-induced gene transcription.

Interleukin 2 receptor expression and interleukin 2 localisation in human solid tumor cells in situ and in vitro: evidence for a direct role in the regulation of tumour cell proliferation

Frozen sections of 52 human solid tumours (38 malignant and 14 benign) of varied histogenesis were immunohistochemically stained with well characterised monoclonal antibodies (MAbs) to human interleukin 2 (IL-2) and the alpha and beta chains of its receptor (R). In all malignant specimens, the tumour cells expressed the IL-2R beta subunit (p75) but not the IL-2R alpha subunit (CD25). In 36 of 38 malignant tumours examined, there was conspicuous staining for IL-2 in the tumour cell nuclei/nucleoli and perinuclear cytoplasm. In the human solid tumour cell lines G361 (melanoma), A549 (lung), MCF-7 (breast) and WiDR (colorectal), both subunits of the IL-2R appeared to be expressed, although the alpha subunit only weakly. Exogenous addition of human recombinant (r) interleukin 2 altered cell numbers in 3 of the 4 cell lines (WiDR was refractory). When grown in the absence of exogenously added rIL-2, IL-2 staining was observed in all cell lines. The pattern of distribution was similar to that exhibited by the tumour cells in situ (i.e., a nuclear/nucleolar localisation). In G361 melanoma cells, this IL-2 staining was present in proliferating cells but disappeared as the cultures approached confluence. Addition of an IL-2R beta subunit blocking antibody to growing G361 cultures (grown in the absence of rIL-2) resulted in a significant reduction in cell numbers. We propose, therefore, that the presence of immunoreactive IL-2 and IL-2R expression is characteristic of human malignant cells and that IL-2 may play a role in the autocrine stimulation of proliferation of malignant cells, such as G361 melanoma cells.

Molecular and structural analysis of nuclear localizing anti-DNA lupus antibodies

To determine the structure of three nuclear localizing lupus anti-DNA immunoglobulins (Igs) and to search for clues to mechanisms of cellular and/or nuclear access, their H- and L-chain variable region sequences were determined and subjected to three-dimensional modeling. Although the results indicate heterogeneity in their primary structures, the H chains are encoded by 3 members of the J558 VH gene family with a common tertiary conformation that is not shared by a J558-encoded nonnuclear localizing anti-DNA control Ig. Furthermore, at least two of the Igs share a conformational motif in the H-chain CDR3, and all three Igs contain multiple positively charged amino acids in their CDRs, resembling nuclear localization signals that direct protein nuclear import. Notably, each VH and VK gene is also found recurrently among previously described autoantibodies. Molecular analysis further indicates that both germline-encoded and significantly mutated V genes can generate nuclear localizing anti-DNA Ig.

Internalization and nuclear localization of peptide hormones

The presence of neuropeptide receptors on the plasma membrane is well accepted, as is its internalization and down-regulation. The analysis of the fate of these peptides within their target-cells is difficult. Endogenous peptides or administered native peptides are visualized in these cells using immunocytology after cryoultramicrotomy. Labelled peptides can be injected and their internalization kinetics studied using ultrastructural autoradiography. The pituitary gland is a suitable model for the study of the neuropeptide mechanism, with the lactotroph function being taken as an example in the present case. Prolactin (PRL) release depends on two main neuropeptides: thyrotropin-releasing hormone (TRH) and somatostatin (SS). The TRH immunoreactivity obtained from endogenous as well as injected material was restricted to the plasma membrane, secretory granules, cytoplasmic matrix and nucleus. The internalization kinetics of exogenous native TRH showed an increase of immunoreactive material in all compartments including the nucleus. The endogenous SSs (SS14 and SS28) were detected in the same subcellular lactotroph compartments. Injection of 125I-SS showed a rapid binding of SS at the plasma membrane level before internalization. For 60 min of in vivo uptake, 125I-SS28, the large SS molecule, was detected in the cytoplasm only, while 125I-SS14 was found in the nuclear matrix. In vitro 125I-SS28 was restricted to the nuclear membrane. Under physiological conditions the endogenous neuropeptides were visualized in the nucleus, but after injection of labelled peptides only small molecules were found in the nucleus. The significance of the presence of these neuropeptides is discussed.

Follicular fluid steroid and epidermal growth factor content, and in vitro estrogen release by granulosa-luteal cells from patients with polycystic ovaries in an IVF/ET program

The follicular fluid (FF) content of androgens, estrogens and epidermal growth factor (EGF) has been evaluated in a group of patients with policystic ovary disease (PCO) and in one of normally-ovulating infertile women (NOW) in an IVF/ET program. The in vitro response to follicle-stimulating hormone (FSH) has been also evaluated in granulosa luteal cells from the same patients. PCO patients showed significantly higher FF androstenedione (delta 4) and testosterone (T) and similar FF estrone (E1) and 17 beta-estradiol (E2) levels compared to controls. In vitro production of E1 and E2 by granulosa luteal cells from PCO patients and from controls were overlapping and their response to FSH was similar. These data indicate a normal intrinsic potential aromatase activity in ovaries from PCO patients stimulated with gonadotropins and suggest that PCOs do not derive from inherent ovarian aromatase deficiency. Increased FF androgen content following gonadotropin stimulation may result from theca cell hyperactivity and androgen accumulation in the follicular antrum of rescued hyperandrogenic follicles as well as from inhibitory factors that may inhibit aromatase activation in vivo, partially counteracting the effect of gonadotropins. FF EGF levels were significantly higher in the group of PCO patients compared to those of NOW. EGF may play a role in blunting the in vivo response of granulosa cells to gonadotropins.

Somatostatin-14 blocks the hepatotrophic effects of insulin in the rat

We hypothesized that somatostatin-14 (SS-14) might inhibit insulin-stimulated hepatic growth. Rat hepatocytes were isolated by a two-step collagenase perfusion technique and cultured on Matrigel. Differentiated hepatocyte function was documented by albumin synthesis. Hepatocytes were incubated with insulin in the presence or absence of SS-14. Hepatocyte proliferation was assessed by tritiated thymidine ([3H]thy) incorporation into DNA. [3H]thy incorporation was increased by 230% in the presence of insulin and was essentially abolished by the addition of SS-14. Insulin-stimulated cyclic-AMP accumulation was also decreased from 190 to 108% of control levels (P less than 0.05) by the addition of SS-14. Pretreatment with pertussis toxin, which inactivates the inhibitory G-protein, Gi, blocked the effect of SS-14.

CONCLUSIONS

(i) In the rat, SS-14 effectively blocks insulin-stimulated [3H]thy incorporation into DNA, possibly by blocking intracellular cAMP accumulation. (ii) Pertussis toxin blocks the growth inhibitory effects of SS-14, suggesting that inhibitory G proteins are involved in the mechanism of SS-14 action. Somatostatin may be useful in studying the role of second messengers in cell growth.

Nuclear localization of endogenous basic fibroblast growth factor in cultured endothelial cells

Indirect immunofluorescence using anti-human placental bFGF antibodies demonstrates the presence of bFGF-like reactivity in the cytoplasm and in the nucleus of adult bovine aortic endothelial cells and of normal and transformed fetal bovine aortic endothelial AG 7680 and GM 7372 cells. Biologically active immunoreactive Mr 18,000 bFGF can be isolated by heparin-Sepharose affinity chromatography from the extract of GM 7372 cell nuclei. Quantitation of bFGF content by biological and immunological methods indicates that 100,000 bFGF molecules per nucleus are present in GM 7372 cells, with nuclear bFGF corresponding to 25-30% of total cellular bFGF. Immunoprecipitation experiments demonstrate that the nuclear localization of newly synthesized bFGF occurs when GM 7372 cells are biosynthetically labeled both in the absence and in the presence of suramin, a molecule that inhibits the binding of bFGF to its plasma membrane receptor. Thus the data indicate that endogenous bFGF undergoes an intracellular sorting to the nucleus of the endothelial cell.

Chromatin and cell surface receptors mediate melanoma cell growth response to nerve growth factor

Growth response to nerve growth factor (NGF) was tested in the primary melanoma cell line WM 164, which expressed a low level of NGF cell-surface receptor, and in WM 164 cells transfected with cDNA for the cell-surface receptor (TrWM 164 cells), which expressed a higher level of the cell-surface receptor. Neither cell line expressed the chromatin receptor for NGF or internalized NGF. Both cell lines were stimulated to growth by NGF. After 10 d of exposure to NGF, a 230,000 Mr chromatin protein (receptor) was induced in both cell lines; as a result, NGF bound to the chromatin, and ribosomal RNA synthesis and cell proliferation were inhibited. We suggest that the cell-surface and chromatin receptors each mediate a different function of NGF.

Basic fibroblast growth factor accumulates in the nuclei of various bFGF-producing cell types

The intracellular localization of basic fibroblast growth factor (bFGF) was studied in BHK-21 cells transfected with an expression vector containing the complementary DNA (cDNA) of the human bFGF gene (pbFGF). The intracellular location of bFGF was determined using indirect immunofluorescence. The antibodies used were polyclonal antibodies directed against either recombinant human bFGF or recombinant Xenopus bFGF. The nuclei of transfected cells that produce bFGF, but not the nuclei of untransfected cells, were labeled strongly by the antibodies. The nuclear staining was totally abolished when anti-bFGF antibodies preadsorbed with bFGF were used. Several types of endothelial cells known to produce bFGF were also stained in their nuclei by the antibodies. Nuclear extracts prepared from transfected cells were found to contain bFGF as determined using heparin-sepharose affinity chromatography, followed by Western blot analysis of fractions, which stimulated the proliferation BHK-21 cells. The mitogenic activity associated with the nuclei was not destroyed when isolated cell nuclei were digested by trypsin. It is therefore likely that the nucleus associated bFGF is intranuclear. These findings suggest that some biological activities of bFGF may be mediated by nuclear bFGF binding proteins or by the direct binding of bFGF to DNA.

Nuclear and cytoplasmic localization of different basic fibroblast growth factor species

The subcellular distribution of basic fibroblastic growth factor (bFGF) was analyzed by subcellular fractionation and immunofluorescence to gain insight into potential mechanisms for its release from cells. Subcellular fractionation of either SK-Hep-1 cells or NIH 3T3 cells transfected with a bFGF cDNA revealed that the 18 kd form of bFGF was found primarily in the cytosolic fraction, whereas the 22 and 24 kd forms of bFGF were found preferentially in ribosomal and nuclear fractions. Analysis of bFGF distribution by immunofluorescence using an antibody that recognized all forms of bFGF indicated both cytoplasmic and nuclear localization but failed to reveal any growth factor in structures representing secretory vesicles. Therefore, bFGF has a distribution inconsistent with that of a secretory protein.

Prospects for epidermal growth factor in the management of corneal disorders

Epidermal growth factor (EGF) is a naturally occurring mitogen which, in its recombinant form, is under intensive investigation for therapeutic use. Receptor activation by EGF induces up-regulation of synthesis of specific proteins as well as proliferation and differentiation of the corneal epithelium, keratocytes, and endothelium both in vivo and in vitro. With topical application of EGF, corneal wounds could possibly heal within hours, and the strength of the stromal scars is also increased; this may lead to the prospect of sutureless surgery. It may be possible to treat degenerative and dystrophic disorders of the cornea, especially of the endothelium, and to enhance the density of endothelial cells in donor corneas prior to transplantation. Combination therapy with EGF, fibroblast growth factor, and corticosteroids may be advantageous in producing a synergistic effect. It is possible that, with increased knowledge of the pharmacokinetics and the development of appropriate delivery systems, EGF could become an integral part of the next generation of ophthalmic pharmaceuticals.

Ligand-induced transformation by a noninternalizing epidermal growth factor receptor

Identification of a mutant epidermal growth factor (EGF) receptor that does not undergo downregulation has provided a genetic probe to investigate the role of internalization in ligand-induced mitogenesis. Contact-inhibited cells expressing this internalization-defective receptor exhibited a normal mitogenic response at significantly lower ligand concentrations than did cells expressing wild-type receptors. A transformed phenotype and anchorage-independent growth were observed at ligand concentrations that failed to elicit these responses in cells expressing wild-type receptors. These findings imply that activation of the protein tyrosine kinase activity at the cell membrane is sufficient for the growth-enhancing effects of EGF. Thus, downregulation can serve as an attenuation mechanism, without which transformation ensues.

Hepatocellular processing of endocytosed proteins

In conclusion, proteins of hepatobiliary transport utilize receptor-mediated endocytosis and intracellular vesicles and rely on functionally dynamic microtubules for their transport by hepatocytes. The many diverse transport pathways in hepatocytes reflect the many functions served by the uptake of various proteins from the blood. The mechanisms of sorting of ligands and their receptors in endosomes and the factors that regulate the intracellular transport pathways are not yet known. Future investigations in this area promise to yield many exciting discoveries about the hepatocellular processing of proteins.

Functional independence of the epidermal growth factor receptor from a domain required for ligand-induced internalization and calcium regulation

We have located the distal boundary of the tyrosine kinase domain of the EGF receptor and have identified a distinct sequence in the C' terminus required for EGF-dependent receptor internalization, leading to receptor down-regulation and degradation. Within this receptor domain, an 18 amino acid highly negatively charged region of predicted helical structure is required both for endocytosis via a high-affinity, saturable pathway and for ligand-stimulated increases in cytosolic calcium. In contrast to kinase-inactive, internalization-competent receptors, kinase-active, internalization-defective receptors effectively signaled gene transcription, morphological transformation, and growth. These observations support the hypothesis that mitogenic responses to EGF are mediated by activation of the intrinsic protein tyrosine kinase activity of the membrane-bound receptor, with ligand-induced internalization serving to terminate the signal.

Effect of oxidative iodination of epidermal growth factor on its binding and secretion by hepatocytes

Experiments were undertaken to determine whether the method of iodination of epidermal growth factor (EGF) affects its binding to rat liver plasma membranes and its uptake, processing, and secretion into bile by intact rat hepatocytes. EGF was iodinated using one of three oxidative reagents: chloramine T (CT), lactoperoxidase (LP), or monochloride (MC). Quantitative receptor binding studies on plasma membranes isolated from male rat livers with either CT-, LP-or MC-125I-EGF indicated no significant difference in the apparent binding constants of the three preparations. To determine whether these three preparations were capable of forming a covalent-like complex with the EGF receptor, they were individually incubated with isolated plasma membranes and subjected to polyacrylamide gel electrophoresis under reducing conditions, followed by autoradiography. Each preparation formed a major radioactive protein band of approximately 180 kD, identified as the EGF receptor by immunoprecipitation with monoclonal anti-EGF receptor antibodies. Furthermore, even unlabeled EGF incubated with plasma membranes formed this same 180 kD band, as revealed on Western blots using anti-EGF antibody. The biliary secretion of CT-, LP-, and MC-125I-EGF was compared by injecting each one into rat portal veins and measuring the total and immunoprecipitable radioactivity in bile. The amount of immunologically intact CT-125I-EGF in bile was significantly greater than the others, whereas MC-125I-EGF transport was significantly reduced. We conclude that the method of iodination does not affect the covalent-like binding properties of EGF. Furthermore, since unlabeled EGF displayed these same binding properties, oxidative iodination procedures per se do not account for the covalent-like association between EGF and its receptor. However, the method of iodination used did affect the intracellular transport and processing of EGF by hepatocytes. The structural modification responsible for this alteration in transport properties has yet to be determined.

Epidermal growth factor (EGF) and monoclonal antibody to cell surface EGF receptor bind to the same chromatin receptor

Cellular uptake, nuclear translocation, and chromatin binding of epidermal growth factor (EGF) and monoclonal antibodies (MAbs) against the protein domain of the EGF surface receptor (MAb 425) and against the carbohydrate Y determinant on the EGF receptor (MAb Br 15-6A) were analyzed in cell lines that express surface EGF receptor. Both EGF and MAb 425 were translocated to the nucleus and bound in nondegraded form to the chromatin of all cells tested. MAb Br 15-6A was taken up only by SW 948 colorectal carcinoma cells which express EGF receptor whereas neither EGF nor MAb 425 was taken up by SW 707 colorectal carcinoma cells which do not express EGF receptor. MAb 425 immunoprecipitated a 230- to 250-kDa chromatin protein, which appears to be the EGF chromatin receptor. EGF was localized in a single EcoRI DNA fragment suggesting that the chromatin binding was highly specific. Binding of EGF to primarily DNase II-sensitive chromatin regions protected these regions from nuclease action. The role of growth factor binding to chromatin in neoplastic transformation is discussed.

Intracellular receptor binding and nuclear transport of nerve growth factor in intact cells and a cell-free system

Nuclear uptake of 125I-labeled nerve growth factor (NGF) by cells that either express or do not express the cell surface receptor was tested using intact cells and a cell-free system. Intracellular and consequently nuclear uptake of NGF in intact cells was dependent on the presence of surface NGF receptor, whereas nuclear uptake in a cell-free system did not correlate with cell surface receptor expression. In the cell-free system, nuclear transport was inhibited when NGF receptor was being actively synthesized. Preincubation of intact cells with unlabeled NGF, cycloheximide, puromycin, or actinomycin D increased nuclear uptake up to threefold. The data suggest that, in intact cells, NGF transported into the cell via the surface receptors is also bound by the NGF receptor being synthesized in the cytoplasm. NGF taken up by the nucleus inhibited transcription of ribosomal RNA genes by 70% and, in turn, inhibited cell proliferation by 60%. A direct effect of NGF on transcription is discussed.

Biological effects of epidermal growth factor, with emphasis on the gastrointestinal tract and liver: an update

Epidermal growth factor (EGF) is a 6,000 Da polypeptide hormone produced by glands of the gastrointestinal tract, namely the salivary and Brunner's glands. It is found in a wide variety of external secretions as well as in blood and amniotic fluid. In fetal and neonatal life, EGF appears to play an important role in the development of the oral cavity, lungs, gastrointestinal tract and eyelids. Its presence in cells of the central nervous system suggests that it also plays a role in modulating the development of this system. In adult animals, the function of EGF is much less well understood. In rodents, it apparently modulates acid secretion from parietal cells in the stomach, and it undoubtedly plays an important role in wound healing, either through its localization within skin or by the licking of wounds with EGF-containing saliva. Considerable evidence now suggests that it may be one of the key factors in initiating liver regeneration after partial hepatectomy or chemical injury. The liver appears to be the principal organ which regulates the circulating level of EGF. In fact, EGF is cleared so efficiently by the liver that only the peripheral cells of the lobule (zone 1) sequester EGF, and little remains in the circulation for cells in the more distal zones (zones 2 and 3). In the liver, EGF normally binds to a plasma membrane receptor and is internalized within the liver cell, where the vast majority of EGF and its receptor are destroyed in lysosomes. A small but consistent quantity of EGF enters the bile intact. In the regenerating liver, however, the lysosomal pathway appears to be shut down, and the EGF is diverted to hepatocyte nuclei prior to the initiation of DNA synthesis. Nuclear EGF is found free as well as bound to a high-molecular-weight protein which has many characteristics identical to the plasma membrane EGF receptor. The plasma membrane receptor is a large transmembrane glycoprotein of 170,000 Da containing four domains: an extracellular EGF-binding portion, a hydrophobic membrane-spanning segment, a proximal cytoplasmic domain which binds ATP and protein substrates containing tyrosine for phosphorylation and a terminal cytoplasmic portion with 3 tyrosines which undergo autophosphorylation after EGF binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Translocation of epidermal growth factor to the hepatocyte nucleus during rat liver regeneration

To determine the fate of exogenous epidermal growth factor (EGF) in regenerating liver, 125I-labeled EGF was injected into rat portal veins at various times after 70% hepatectomy. Epidermal growth factor was taken up by the liver remnant at all time points studied (0, 4, 8, 16, and 36 h), but at 8 h after hepatectomy a large quantity was retained by the liver and EGF degradation products appearing in the bile decreased markedly. Electron microscopic autoradiography of the regenerating livers 1 h after injection of 125I-EGF demonstrated that 27% of the grains were associated with hepatocyte nuclei compared to 0.5% in shamoperated controls. There was also a concomitant decrease in grains associated with the lysosomal compartment. Nuclei isolated from regenerating livers exposed to 125I-EGF also demonstrated a three-fold increase in radioactivity compared to nuclei from control livers. Nearly 70% of nuclear radioactivity was precipitable with a specific antibody to EGF, and a small fraction appeared to be part of a high molecular weight complex. These data support the hypothesis that during the pre-S phase of liver regeneration, EGF is translocated to the nucleus rather than to lysosomes, and may participate in the initiation of deoxyribonucleic acid synthesis or alteration of gene expression.

Biochemical and ultrastructural processing of [125I]epidermal growth factor in rat epidermis and hair follicles: accumulation of nuclear label

Although the intracellular ultrastructural processing of epidermal growth factor (EGF) and its receptor have been described in cell culture systems, very few studies have examined this phenomenon in intact tissues. We have examined the ultrastructural and biochemical handling of [125I]EGF in the epidermis and hair follicle bulb of intact, viable, 3- to 5-day-old rat skin the EGF receptor distribution of which has already been documented and in which EGF has been shown to be biologically active. After incubation of explants with 10 nM [125I]EGF for 2.5 h at 25 degrees or 37 degrees C, radiolabel was detected over the basal cells of the epidermis and hair follicle outer root sheath, confirming previous light microscope observations. More specifically, silver grains were observed near coated and uncoated plasma membrane and coated membrane invaginations, Golgi apparatus, lysosomal structures, and nuclei. Sodium azide inhibited internalization of label, whereas a series of lysosomal inhibitors (chloroquine, monensin, and iodoacetamide) caused a slight increase in silver grains associated with lysosomal vesicles and a decrease in nuclear label. Biochemical analysis indicated that greater than 35% of radioactivity following incubation at 37 degrees C was in the form of degraded [125I]EGF fragments and that inclusion of chloroquine, monensin, and iodoacetamide reduced this value to 20.8%, 8.6%, and 4.0%, respectively. In addition, chloramine T-prepared [125I]EGF was found to be covalently cross-linked with low efficiency to a protein having the molecular weight of the EGF receptor. These data are discussed in the light of the effects of EGF on epithelial cell proliferation in skin.

Comparative study of antithrombin III.protease complex metabolism by fibroblasts and vascular endothelial cells

125I-labeled human antithrombin III (125I-AT III).protease complexes are specifically bound to both cultured human skin fibroblast (HSF) cells and adult bovine aortic endothelial (ABAE) cells; however, there is a significant difference in the rate and degree of metabolism of the complexes by these two cell types. HSF cells appear to internalize the complexes at a rate of about 2.5 pmole/1 X 10(6) cells/h and subsequently degrade them at a rate of 0.6 pmole/1 X 10(6) cells/h. ABAE cells internalize and degrade the complexes at rates approximately 100 and 30 times lower, respectively. Neither cell type interacts with free 125I-AT III but only with its combined form with either thrombin or trypsin. These data indicate the major role of HSF cells in the removal of AT III.protease complexes from extravascular spaces in the body, in contrast to the inert vascular surface with regard to AT III.protease complexes provided by the vascular endothelium.

Chloroquine and primary amines inhibit the internalization of antithrombin III.trypsin complex in cultured cells

Bovine corneal endothelial (BCE) cells have been shown to specifically bind, internalize and degrade antithrombin III (AT III).protease complexes as well as thrombin. Previous studies have indicated that chloroquine has no effect on the internalization of thrombin or other cell surface-bound ligands, but it inhibits their subsequent degradation. In contrast, the present study demonstrates the unique inhibitory effect of chloroquine on the internalization of 125I-AT III.trypsin complex by BCE cultures. Similarly, the primary amines, monodansylcadaverine and methylamine, inhibit the internalization of 125I-AT III.trypsin complex, but not the internalization of 125I-thrombin. The various amines used in this study revealed: (1) differences in the process of cellular binding and internalization between AT III.protease complex and thrombin, although the degradation of both internalized ligands proceed in an analogous manner; and (2) the unique sensitivity to chloroquine of 125I-AT III.trypsin complex internalization by cultured cells. These results might indicate that AT III.protease complexes are internalized via a distinct receptor and/or a different mechanism from thrombin.

Binding and processing of trypsin by cultured bovine corneal endothelial cells

Bovine corneal endothelial cells in culture bind internalize and degrade [125I]-trypsin. Binding involves the active site of trypsin and increases as a function of [125I]-trypsin concentration. Saturation is observed at a concentration of 0.5-1.0 micrograms ml-1. The cell surface binding of [125I]-trypsin is specific: a seven-fold excess of unlabeled trypsin abolishes about 60% of the total cell surface-associated radioactivity. In addition, thrombin competes poorly with [125I]-trypsin cell surface binding and only 20% of the specific cell surface binding of [125I]-trypsin is subjected to competition with thrombin. This fraction of the cell surface-bound [125I]-trypsin which is accessible to competition with thrombin appears in a covalent complex of [125I]-trypsin X protease-nexin with a molecular weight of 64000 daltons. The cells, when incubated at 37 degrees C, appear to internalize the cell surface-bound [125I]-trypsin at a rate of 0.15-0.25 ng (10(6) cells)-1 min-1. Both the non-covalently cell surface-bound and the protease-nexin (PN) mediated-bound [125I]-trypsin are internalized by the cells, but the [125I]-trypsin X PN complexes contribute about 75% of the total amount of [125I]-trypsin internalized by the cells. The internalized [125I]-trypsin is degraded by the cultures at a rate of about 0.05 ng (10(6) cells)-1 min-1 and the degradation products are released by the cells into the incubation medium as a trichloroacetic acid non-precipitable material. Chloroquine inhibits about 60% of the internalization of [125I]-trypsin by the cells, and inhibits more than 80% of the degradation process of [125I]-trypsin, which indicates that the degradation of the ligand is taking place in lysosomes. Bovine corneal endothelial cells in culture have demonstrated the binding and metabolism of the serine protease trypsin. This described process may indicate the ability of corneal endothelial cells to control the activity of serine proteases in their microenvironment.

Correlation between trypsin binding to a specific receptor and prostacyclin production in cultured vascular endothelial cells

The correlation between the binding and processing of trypsin and its effect on prostacyclin (PGI2) production in cultured adult bovine aortic endothelial (ABAE) cells was studied. ABAE cells demonstrated an ability to produce PGI2 in a dose-response manner to trypsin at the range of 0.1-2.0 micrograms/ml with a saturation at a concentration of 1 microgram/ml. Likewise, 125I-trypsin binding to the cultured cells increased in a dose-response way and reached saturation at a concentration of about 1 microgram/ml; 125I-trypsin was bound to a specific high-affinity cell-surface receptor with a dissociation constant (Kd) of 1.5 X 10(-8) M and each of the confluent ABAE cells has about 1.2 X 10(5) such receptors sites. The cell-surface receptor for trypsin displayed specific characteristics and an excess amount of unlabeled trypsin successfully abolished 125I-trypsin binding while thrombin in excess failed to compete for 125I-trypsin binding. Only a small fraction of the cell-surface-bound 125I-trypsin was internalized and subsequently degraded by ABAE cells as compared to the process of 125I-trypsin internalization by human skin fibroblasts (HSF). This study demonstrated that the stimulatory effect of trypsin on prostacyclin production and release by ABAE cells might be mediated by a specific cell-surface receptor for trypsin on these cells distinct from the thrombin receptor.

[Epidermal growth factor: structure, location, phosphorylation and regulation of its receptor]

Epidermal growth factor (EGF) is a Mr 6045 polypeptide first characterized for its ability to stimulate mitogenesis in epidermal and epithelial cells. The first step in the action of the growth factor is its binding to specific, high affinity membrane receptors. These receptors have been studied in a number of tissues and cell culture lines. The level of EGF receptors is modulated by many agents. EGF down-regulates its receptor. In addition, the number of EGF receptors is decreased by other growth factors (platelet-derived growth factor; transforming growth factor), by many tumor promoters and by viral transformation. Several hormones also can regulate EGF binding in its target tissues.

Covalent attachment of 125I-beta nerve growth factor to its receptors on sympathetic neurons

When 125I-beta nerve growth factor binds to sympathetic and sensory neurons, some labeled ligand is sequestered (becomes inaccessible to the external milieu) in a time- and energy-dependent manner. It would appear that the higher affinity receptor (type I) participates in this process to a greater extent than does the lower affinity receptor (type II) [ Olender and Stach , 1980; Olender et al., 1981]. A small portion of the sequestered 125I-beta nerve growth factor is found as part of a high molecular weight complex. When cells, which have been incubated with 125I-beta nerve growth factor, are solubilized with Triton X-100 and subjected to sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis, a complex with an apparent molecular weight of approximately 240,000 is obtained. The formation of the covalent complex can be prevented by the prior addition of excess unlabeled beta nerve growth factor or sodium fluoride and dinitrophenol. The covalent 125I-beta nerve growth factor-receptor complex is dissociated in 50 mM dithiothreitol indicating that disulfide linkages are involved. At concentrations of beta nerve growth factor (3.8 X 10(-11) -3.8 X 10(-10) M) where maximal fiber outgrowth occurs in vitro, approximately 50-266 attomoles (0.3-1.6% of the type I receptors) of the covalent complex are formed per 10(7) nerve cells. These data suggest that a small portion of the 125I-beta nerve growth sequestered by sympathetic neurons becomes covalently attached to its receptor subsequent to its sequestration in a manner which appears to involve type I receptors.

Growth factors and their action in vivo and in vitro

The molecular nature and mechanism of action of several of the growth factors including epidermal growth factor, fibroblast growth factor and platelet-derived growth factor is reviewed. The ectopic production of growth factors may be important in the growth development of certain tumours. In addition, attention is directed to the importance of the extracellular matrix in controlling cell proliferation and differentiation.

Organ and species specificity of the messenger RNA transport factor

The transport of messenger RNA from isolated rat liver nuclei is dependent on a 35,000 dalton protein localized in the cytoplasm. The tissue and species specificity of this protein are reported. The factor from female rat liver or from rat brain, kidney, or hepatoma supports the transport of messenger RNA from male rat liver nuclei. Messenger RNA is also transported in response to the factor from beef and chicken liver. The cytosols from rat erythrocytes, amoeba and yeast were inactive in the rat liver system. The results indicate that the messenger RNA transport factor is not specific for the nucleotide sequence of the coding portion of the messenger RNA and that it is not organ or species specific within the vertebrates.