An acidic fibroblast growth factor stimulates DNA synthesis, inhibits collagen and alkaline phosphatase synthesis and induces resorption in bone

We have examined the effects of an acidic fibroblast growth factor (aFGF) on bone cell growth and differentiation and on osteoclastic resorption using rat fetus organ cultured calvariae and long bones, respectively. Low concentrations of this aFGF stimulated DNA synthesis (1.28 ng/ml) and inhibited collagen formation (1.28 ng/ml) and alkaline phosphatase activity (0.64 ng/ml) in the isolated calvariae. The inhibition of collagen synthesis was independent of the aFGF's mitogenic effect, and was evident in periosteum-containing and periosteum-free bones, pointing to osteoblasts as the aFGF-responsive cells. Our preparation of aFGF enhanced resorption in the long bones by a calcitonin-inhibitable mechanism. PGE2 release accompanied and indomethacin prevented the enhancement of resorption. By contrast, indomethacin did not block the stimulation of DNA and collagen synthesis caused by our aFGF. These results indicate that our aFGF exerts a PGE2-independent effect on DNA synthesis and collagen synthesis and a PGE2-dependent effect on resorption in bone tissue in vitro.

Polymorphic DNA haplotypes at the phenylalanine hydroxylase (PAH) locus in Asian families with phenylketonuria (PKU)

DNA polymorphisms at the phenylalanine hydroxylase (PAH) locus have proved highly effective in linkage diagnosis of phenylketonuria (PKU) in Caucasian families. More than 10 RFLP sites have been reported within the PAH structural locus in Caucasians. With information from affected and unaffected offspring in PKU families it is often possible to reconstruct complete RFLP haplotypes in parents and to use these haplotypes to follow the segregation of PKU within families and to determine the distribution of PKU chromosomes within populations. To establish the utility of these RFLPs in characterizing Asian families with PKU, we typed eight DNA sites in 21 Chinese families and 12 Japanese families with classical PKU. The eight RFLPs were chosen for their informativeness in Caucasians. From these families we reconstructed a total of 91 complete PAH haplotypes, 44 from non-PKU chromosomes and 47 from PKU-bearing chromosomes. Although all eight marker sites are polymorphic in both Chinese and Japanese, there is much less haplotypic variation in Asians than in Caucasians. In particular, one haplotype alone, haplotype 4, accounts for more than 77% of non-PKU chromosomes and for more than 80% of PKU-bearing chromosomes. Haplotype 4 is also relatively common in Caucasians. The next most common Asian haplotype is 10 times less frequent than haplotype 4. By contrast, in many Caucasian populations the sum of the frequencies of the five most common haplotypes is still less than 80%, and several of the most common haplotypes are equally frequent. Even though the extent of haplotypic variation in Asians is severely limited, the few haplotypes that are found often differ at a number of RFLP sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Aicardi syndrome--a case report

The Aicardi syndrome was first described by Aicardi in in 1965, which consisted of infantile spasms, defect of the corpus callosum, a characteristic lacunar chorioretinopathy, mental subnormality, and costovertebral anomalies. All patients have been female except one male case was reported in Australia. There have been approximately over 100 cases of the Aicardi syndrome reported in the literatures since 1965. The etiology of this syndrome is unknown. The most likely cause, however, is an X-linked mutational event with lethality in hemizygous male. We report a 43-day-old female infant with classic features of Aicardi syndrome including flexion spasms, dysgenesis of corpus callosum, microphthalmia, characteristic EEG, and characteristic lacunar chorioretinopathy.

Evidence for retrograde degeneration of epinephrine neurons in Alzheimer's disease

Alzheimer's disease (AD) is associated with a progressive loss of locus ceruleus neurons. These noradrenergic neurons receive a major afferent projection from epinephrine neurons in epinephrine cell groups in the brainstem. The epinephrine neurons have a specific enzymatic marker, phenylethanolamine N-methyltransferase (PNMT), which allows them to be identified chemically and immunohistochemically. We have previously reported a decrease in PNMT in brains of patients with AD. We now report that the decrease in PNMT activity in projections to the locus ceruleus is not due to the loss of epinephrine neurons, although up to 33% of these neurons are atrophic. The decrease in presynaptic PNMT does, however, correlate with the loss of postsynaptic locus ceruleus neurons in brains from AD patients. The percentage of degenerating neurons in the epinephrine nuclei also correlates significantly with the amount of loss of locus ceruleus neurons in AD. In addition, there is a 55% decrease in mitogen activity, a nonspecific measure of growth or maintenance factors, in dialysed locus ceruleus extracts from the AD patients compared to those from control subjects. The mitogen activity in the locus ceruleus was significantly correlated with PNMT activity and with the density of locus ceruleus neurons in all cases examined. These findings provide evidence for the hypothesis that retrograde degeneration is a mechanism of neuronal degeneration in AD and suggest that trophic factors may play a role in this process.

Rapid turnover of the platelet-derived growth factor receptor in sis-transformed cells and reversal by suramin. Implications for the mechanism of autocrine transformation

In cells transformed by either v-sis or c-sis, the majority of the newly synthesized platelet-derived growth factor (PDGF) receptors fail to reach the cell surface and are rapidly degraded. This rapid turnover (t1/2 less than 30 min) appears to result from interaction of the sis gene product with the PDGF receptor in the endoplasmic reticulum and/or Golgi apparatus during their intracellular routing from the endoplasmic reticulum to the plasma membrane or extracellular compartment. Several lines of evidence support this hypothesis. 1) Both the 160-kDa precursor and the intracellular 180-kDa mature form of the PDGF receptor possessed ligand binding activity for PDGF; 2) both the 160-kDa precursor and the 180-kDa mature form of the receptor in sis-transformed cells were found to be activated (phosphorylated); 3) protamine, a competitive inhibitor for PDGF or v-sis gene product binding to the cell-surface receptor, did not affect the rapid turnover of the PDGF receptor in sis-transformed cells; 4) suramin, an inhibitor for PDGF or v-sis gene product binding to the PDGF receptor, not only reversed the rapid turnover of the PDGF receptor in sis-transformed cells, but also increased the secretion of sis gene products; and 5) rapid turnover of the PDGF receptor was only observed in sis-transformed cells but not in cells transformed by other oncogenes. We suggest that the persistence of a mitogenic signal from cellular organelles, arising from the intracellular interaction of sis gene products with newly synthesized PDGF receptors, is the mechanism for autocrine transformation by sis.

Characterization of the spectrum of postthymic T-cell malignancies in Taiwan. A clinicopathologic study of HTLV-1-positive and HTLV-1-negative cases

Postthymic T-cell malignancy shows marked geographic, clinicopathologic, and prognostic diversity. The frequency and spectrum of T-cell malignancies in Taiwan were investigated. Fifty-two patients (35 male and 17 female) with a median age of 49 years, were consecutively encountered between October 1983 and April 1987; these accounted for 39% of non-Hodgkin's lymphoma cases seen in our institutions. Ten patients (19.3%) had adult T-cell leukemia/lymphoma (ATL) associated with human T-cell leukemia virus (HTLV-1). Patients with ATL had disease similar to that reported from southwestern Japan and the Caribbean. They had frequent skin lesions (60%), hypercalcemia (40%), and a rapid clinical course with a median survival of 1.3 years. The 35 HTLV-1-negative peripheral T-cell lymphomas (PTL) were similar to PTL in western countries, manifesting frequent visceral, cutaneous, and vascular tropisms. Marrow involvement was documented at presentation in 39% and Stage III/IV disease in 80% of the PTL patients. The histology of PTL usually expressed prominent reactive features which is distinct from that in ATL. Several subcategories could be defined: Hodgkin's-like PTL in nine patients, T-zone lymphoma in three, angioimmunoblastic lymphadenopathy-like lymphoma in one, Lennert's lymphoma in three, and angioinvasive lymphoma in four. Two HTLV-1-negative PTL had neoplastic cells with clover-shaped nuclei and were designated as ATL-like. Morphologic classification based on the modified Working Formulation showed prognostic correlation, with median survival of less than 6 months for large cell/immunoblastic PTL, compared with 5 years for patients with small/medium cell PTL. Both low- and high-grade PTL seem to represent an incurable disease. Classical cutaneous T-cell lymphoma (seven cases) is relatively unusual in Taiwan, compared with the frequency of PTL. Post-thymic T-cell malignancies in Taiwan include HTLV-1-positive and HTLV-1-negative diseases, both of which have a poor prognosis and resemble similar T-cell malignancies in the East and West.

Modulation of the epidermal growth factor receptor by brain-derived growth factor in Swiss mouse 3T3 cells

Incubation of Swiss mouse 3T3 cells at 37 degrees C with bovine brain-derived growth factor (BDGF) decrease the cell surface 125I-EGF binding activity of these cells by 70-80%. This down-modulation of the EGF receptor by BDGF was time, temperature, and dose dependent. Scatchard plot analysis indicated that BDGF binding led to a selective decrease in the number of high-affinity EGF receptors. The BDGF-induced down-modulation of the EGF receptor was completely blocked by protamine, a potent inhibitor of receptor binding and mitogenic activities of BDGF. BDGF down-modulated the EGF receptor in phorbol myristic acetate (PMA)-pretreated cells, as well as in control cells. Furthermore, PMA-pretreated cells responded mitogenically to BDGF, whereas PMA itself failed to stimulate the mitogenic response of PMA-pretreated cells. This BDGF-induced down-modulation of the EGF receptor in PMA-desensitized cells suggests that BDGF down-regulates the EGF receptor by a mechanism distinct from that of PMA. Incubation of cells with compounds which are known to inhibit pinocytosis blocked the down-modulation induced either by BDGF or by platelet-derived growth factor (PDGF) but had no effect on the PMA-induced down-modulation. Incubation of cells with inhibitors of receptor recycling enhanced the BDGF-induced down-modulation of the EGF receptor. These results suggest that BDGF and PDGF induce down-modulation of the EGF receptor by increasing the internalization of cell surface high-affinity receptors and that the internalization process may not be required for down-modulation induced by PMA.

Human transforming growth factor beta.alpha 2-macroglobulin complex is a latent form of transforming growth factor beta

125I-Labeled human platelet-derived transforming growth factor beta (125I-TGF-beta) and human alpha 2-macroglobulin (alpha 2M) formed a complex as demonstrated by 5% native polyacrylamide gel electrophoresis. The 125I-TGF-beta.alpha 2M complex migrated at a position identical to that of the fast migrating form of alpha 2M. Most of the 125I-TGF-beta.alpha 2M complex could be dissociated by acid or urea treatment. When 125I-TGF-beta was incubated with serum, the high molecular weight form of 125I-TGF-beta could be immunoprecipitated by anti-human alpha 2M anti-sera as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. alpha 2M purified from platelet-rich plasma also showed the latent transforming growth factor activity and immunoreactivity of TGF-beta. These results suggest that TGF-beta.alpha 2M complex is a latent form of TGF-beta.

Neuron localization and neuroblastoma cell expression of brain-derived growth factor

Bovine brain-derived growth factor (BDGF) is a approximately 16-17 kD polypeptide mitogen with a broad spectrum of cell specificity. Using a highly specific mouse polyclonal anti-BDGF antiserum for indirect immunoperoxidase and immunofluorescent stainings, BDGF was found to be specifically localized in the neurons of bovine brain cortex. The indirect immunofluorescent staining was blocked by the presence of excess purified BDGF. Human neuroblastoma cells showed cytoplasmic staining with anti-BDGF antiserum. The cell lysates of neuroblastoma cells elicited a BDGF-like activity which could be completely inhibited by preincubation with anti-BDGF antiserum.

Brain-derived growth factor is a chemoattractant for fibroblasts and astroglial cells

Bovine brain-derived growth factor (BDGF), a 16-17 kDa protein with biochemical properties resembling brain-derived acidic fibroblast growth factor (acidic FGF) and endothelial cell growth factor, was found to have potent chemotactic activity for bovine ligament fibroblasts, human skin fibroblasts and rat astroglial cells, maximal at 100-200 pg/ml. The chemotactic activity was completely blocked by protamine sulfate (5 ug/ml), an inhibitor of receptor-binding and mitogenic activity of BDGF. BDGF did not stimulate migration of human monocytes. These results indicate that the effects of BDGF 'in vivo' might extend to mesenchymal cell recruitment.

Transforming growth factor activity of bovine brain-derived growth factor

Bovine brain-derived growth factor (BDGF), whose biochemical properties resemble those of endothelial cell growth factor (ECGF) and brain-derived acidic fibroblast growth factor (acidic FGF), is able to promote colony formation of normal rat kidney fibroblasts (NRK cells) in soft agar. As in the case of transforming growth factor beta (TGF beta), EGF potentiates the anchorage-independent growth promoting activity of BDGF. In the presence of EGF (5 ng/ml), the optimal concentration of BDGF for stimulation of anchorage-independent of NRK cells is approximately 0.5 ng/ml. At higher concentrations, BDGF becomes inhibitory. The anchorage-independent cell growth promoting activity of BDGF differs from that of TGF beta in acid and reducing agent stability.

Bovine brain-derived growth factor. Purification and characterization of its interaction with responsive cells

A large-scale purification procedure for brain-derived growth factors, without chromatography in 0.1% trifluoracetic acid, has been developed. Two related brain-derived growth factors have been purified to homogeneity from bovine brain using this procedure involving ammonium sulfate fractionation, followed by chromatography on CM-Sephadex C-50, sulfated Sephadex G-50, and heparin-Sepharose 4B. Brain-derived growth factor A (BDGF-A, molecular weight approximately 16,000) and brain-derived growth factor B (BDGF-B, molecular weight approximately 17,000) were eluted from heparin-Sepharose 4B at 1.2 and 1.6 M NaCl, respectively. Both BDGF-A and BDGF-B have a pI value of 5.7, have the same specific mitogenic activity, and react with mouse anti-BDGF-A antiserum. Both growth factors have a broad spectrum of mitogenic activity (vascular and aorta endothelial cells, chondrocytes, osteoblasts, epithelial cells, glial cells, fibroblasts, and smooth muscle cells), with a half-maximum effect at 10-20 pM. The binding of BDGF to bovine aorta endothelial cells and Swiss mouse 3T3 cells has been characterized. Binding of 125I-BDGF-A to these cells reached equilibrium in less than 15 min. Scatchard plot analysis of the binding of 125I-BDGF-A to endothelial cells and 3T3 cells showed a single class of high-affinity receptor with Kd values of 20 +/- 5 and 13 +/- 3 pM and receptor numbers/cell of 7,000 +/- 1,000 and 20,000 +/- 3,000, respectively. BDGF-B competed for 125I-BDGF-A binding in the same manner as unlabeled BDGF-A, suggesting that BDGF-A and BDGF-B bind to the same receptor. Basic pituitary fibroblast growth factor appeared to be a weak inhibitor, whereas platelet-derived growth factor and epidermal growth factor had no effect on 125I-BDGF-A binding. Protamine, histone, polylysine, and polyarginine are potent inhibitors of the mitogenic activity of BDGF-A and BDGF-B and of binding of 125I-BDGF-A to responsive cells. The half-time (t1/2) of internalization and degradation of cell surface-bound 125I-BDGF is 3 h.

Association of bovine brain-derived growth factor receptor with protein tyrosine kinase activity

Bovine brain-derived growth factor (BDGF) is very similar to endothelial cell growth factor and brain-derived acidic fibroblast growth factor in terms of pI (5.7) and molecular weight (approximately 17,000). BDGF has a wide spectrum of cell specificity, including bovine aorta endothelial cells and Swiss mouse 3T3 cells. BDGF stimulates the phosphorylation of a 135-kDa protein in plasma membranes of 3T3 cells. The optimal concentration for stimulation of phosphorylation is close to the Kd of 125I-BDGF binding to receptor, suggesting that the BDGF-stimulated 32P-labeled 135-kDa protein may be the BDGF receptor. The alkaline stability of this 32P-labeled 135-kDa phosphoprotein and phosphoamino acid analysis of the acid hydrolysates indicate that the phosphorylation occurs at tyrosine residues. The molecular size of BDGF receptor is estimated as approximately 135 kDa by cross-linking 125I-BDGF to its receptor in 3T3 cells, using a bifunctional reagent, ethylene glycolbis(succinimidylsuccinate). Both BDGF-stimulated phosphorylation and 125I-BDGF binding to receptor can be inhibited by protamine. These results suggest that the BDGF receptor is a 135-kDa protein which is associated with a protein tyrosine kinase activity.

Transforming protein of simian sarcoma virus stimulates autocrine growth of SSV-transformed cells through PDGF cell-surface receptors

Simian sarcoma virus-transformed NIH 3T3 (SSV-NIH 3T3) and SSV-NRK cells secrete a potent growth-promoting activity identical with the platelet-derived growth factor (PDGF) in mitogenic assays. The secreted activity is blocked by anti-PDGF antisera and competes with 125I-PDGF for receptor binding, suggesting that the secreted protein is the transforming protein of SSV, p28v-sis, or its processed product. Secreted p28v-sis appears to stimulate autocrine cell growth of SSV-transformed cells because anti-PDGF antisera block 3H-thymidine incorporation into growing SSV-NIH 3T3 and SSV-NRK cells. SSV-transformed cells have reduced numbers of high-affinity 125I-PDGF receptors; PDGF/p28v-sis receptor was purified from SSV-NIH 3T3 cells and retained active protein tyrosine kinase activity stimulated by PDGF. The rate of tumor growth in athymic nude mice injected with SSV-transformed cells was compared with levels of secreted growth factor activity. The rate of tumor growth in nude mice correlated directly with levels of p28v-sis secreted by SSV-transformed cells.

IgE immune complexes induce immediate and prolonged release of leukotriene C4 (LTC4) from rat alveolar macrophages

Alveolar macrophages obtained by lung lavage from rats were incubated with monoclonal mouse anti-DNP IgE and specific antigen (DNP-HSA) and were found to release a slow reacting substance (SRS), which was characterized by high performance liquid chromatography as leukotriene C4 (LTC)4. Alveolar macrophages incubated with 1 microM A23187 (calcium ionophore) released similar amounts of SRS (6.0 +/- 2.2 and 5.7 +/- 3.7 X 10(-10) mol of LTC4 per 5 X 10(6) alveolar macrophages, respectively). The optimal conditions and mechanism of LTC release by IgE and antigen were examined. LTC4 release was maximal when freshly retrieved alveolar macrophages were incubated for 20 min with 10 micrograms/ml IgE and then for 20 min with 100 ng/ml antigen or for 20 min with IgE and antigen that had been preincubated together for 30 min at room temperature. In addition, LTC4 release was maximal when cells were challenged with IgE and antigen in a protein-free balanced salt solution and when the cells were tumbled to prevent adherence. Dose response experiments revealed that macrophages released LTC4 when stimulated with as little as 10 ng IgE and 100 ng DNP-HSA. Alveolar macrophages did not release LTC when challenged with IgE or DNP-HSA alone. Activation of LTC4 release by IgE and antigen was rapid in onset (2.5 to 5 min), and washing to remove fluid phase IgE and antigen revealed that once activated, alveolar macrophages were capable of prolonged and continuous release of LTC4. Peritoneal lavage cells stimulated with IgE and antigen did not release SRS but could release SRS when incubated with A23187 (5.7 +/- 1.3 X 10(-10) mol LTC4/5 X 10(6) macrophages). A large variability existed between individual rats in the ability of their alveolar macrophages to be activated by IgE and antigen to release LTC4. DNP-HSA labeled with 125I was used to show formation of immune complexes of IgE and antigen when IgE and antigen were incubated together before macrophage challenge. IgE immune complexes containing as little as 2 ng of antigen elicited the release of LTC4 from alveolar macrophages. These data indicate that rat alveolar macrophages release primarily LTC4 when challenged with IgE immune complexes, and that the alveolar macrophage may differ in this respect from peritoneal macrophages that do not release detectable quantities of LTC4 when challenged under identical conditions.

IgE immune complexes induce immediate and prolonged release of leukotriene C4 (LTC4) from rat alveolar macrophages

Alveolar macrophages obtained by lung lavage from rats were incubated with monoclonal mouse anti-DNP IgE and specific antigen (DNP-HSA) and were found to release a slow reacting substance (SRS), which was characterized by high performance liquid chromatography as leukotriene C4 (LTC)4. Alveolar macrophages incubated with 1 microM A23187 (calcium ionophore) released similar amounts of SRS (6.0 +/- 2.2 and 5.7 +/- 3.7 X 10(-10) mol of LTC4 per 5 X 10(6) alveolar macrophages, respectively). The optimal conditions and mechanism of LTC release by IgE and antigen were examined. LTC4 release was maximal when freshly retrieved alveolar macrophages were incubated for 20 min with 10 micrograms/ml IgE and then for 20 min with 100 ng/ml antigen or for 20 min with IgE and antigen that had been preincubated together for 30 min at room temperature. In addition, LTC4 release was maximal when cells were challenged with IgE and antigen in a protein-free balanced salt solution and when the cells were tumbled to prevent adherence. Dose response experiments revealed that macrophages released LTC4 when stimulated with as little as 10 ng IgE and 100 ng DNP-HSA. Alveolar macrophages did not release LTC when challenged with IgE or DNP-HSA alone. Activation of LTC4 release by IgE and antigen was rapid in onset (2.5 to 5 min), and washing to remove fluid phase IgE and antigen revealed that once activated, alveolar macrophages were capable of prolonged and continuous release of LTC4. Peritoneal lavage cells stimulated with IgE and antigen did not release SRS but could release SRS when incubated with A23187 (5.7 +/- 1.3 X 10(-10) mol LTC4/5 X 10(6) macrophages). A large variability existed between individual rats in the ability of their alveolar macrophages to be activated by IgE and antigen to release LTC4. DNP-HSA labeled with 125I was used to show formation of immune complexes of IgE and antigen when IgE and antigen were incubated together before macrophage challenge. IgE immune complexes containing as little as 2 ng of antigen elicited the release of LTC4 from alveolar macrophages. These data indicate that rat alveolar macrophages release primarily LTC4 when challenged with IgE immune complexes, and that the alveolar macrophage may differ in this respect from peritoneal macrophages that do not release detectable quantities of LTC4 when challenged under identical conditions.

Specific covalent binding of platelet-derived growth factor to human plasma alpha 2-macroglobulin

Attempts to measure the platelet-derived growth factor (PDGF) in human plasma resulted in the discovery of a specific plasma binding protein. The 125I-labeled PDGF (125I-PDGF)-plasma binding protein complex retained mitogenic activity but lost reactivity against rabbit anti-PDGF antiserum. Copurification of the plasma binding protein and alpha 2-macroglobulin (alpha 2M) in human plasma, the formation of a complex between 125I-PDGF and purified alpha 2M, and the comigration of the 125I-PDGF-plasma binding protein complex and the 125I-PDGF-alpha 2M complex in NaDodSO4/polyacrylamide gel electrophoresis and in pore-limiting polyacrylamide gel electrophoresis strongly suggested that alpha 2M is the plasma binding protein for 125I-PDGF. Immunoprecipitation of 125I-PDGF-alpha 2M and 125I-PDGF-plasma binding protein complexes by anti-human alpha 2M antiserum further established that alpha 2M and the plasma binding protein are the same molecule. Approximately 20% of 125I-PDGF is complexed by alpha 2M; further 125I-PDGF is complexed if the remaining 125I-PDGF is incubated with additional alpha 2M. Complex formation of 125I-PDGF with plasma or with alpha 2M was completely inhibited by 0.2 mM p-chloromercuric benzoate or 0.2 mM N-ethylmaleimide. The 125I-PDGF-alpha 2M complex or 125I-PDGF-plasma binding protein complex was not dissociated by 8 M urea, 1 M acetic acid, 0.1 M NaOH, or 1% NaDodSO4 but was dissociated by 2-mercaptoethanol, suggesting that the covalent binding of 125I-PDGF to alpha 2M occurs through a disulfide/sulfhydryl exchange reaction. The 125I-PDGF-alpha 2M complex (780,000 daltons) appears to contain two molecules of 125I-PDGF and two dimers of alpha 2M. The precise physiological role of the 125I-PDGF-alpha 2M interaction is unknown. alpha 2M may serve to limit PDGF released locally at sites of blood vessel injury. Alternatively, because of the nearly complete homology between the partial amino acid sequence of PDGF and the predicted amino acid sequence of the transforming protein of the simian sarcoma virus, p28sis, alpha 2M may play an important role in limiting the activity of a PDGF-like activity expressed by virus-transformed cells.

Protamine inhibits platelet derived growth factor receptor activity but not epidermal growth factor activity

Protamine sulfate blocked 125I-PDGF binding to its specific physiological receptor on Swiss mouse 3T3 cells. Reduced 125I-PDGF binding in the presence of protamine sulfate correlated directly with a protamine sulfate dose-dependent decrease in the PDGF-dependent incorporation of [3H]-thymidine into 3T3 cells and a decreased PDGF-stimulated tyrosine-specific protein kinase activity in isolated membrane preparations of 3T3 cells. Protamine sulfate blocked 125I-PDGF binding to simian sarcoma virus transformed cells (SSV-NIH 3T3 and SSV-NP1 cells) and to nontransformed cells in a manner qualitatively identical to unlabelled PDGF. In contrast, protamine sulfate enhanced the specific binding of 125I-EGF by increasing the apparent number of EGF receptors on the cell surface. The increase in 125I-EGF receptor binding was not prevented by cycloheximide nor by actinomycin D. Protamine sulfate did not affect 125I-EGF binding to membranes from 3T3 cells or the EGF-stimulated 3T3 cell membrane tyrosine specific protein kinase activity, suggesting that protamine sulfate may have exposed a population of cryptic EGF receptors otherwise not accessible. Protamine sulfate was fractionated into four active fractions by Sephadex G-50 gel filtration columns; the half maximum inhibition concentration of 125I-PDGF binding to 3T3 cells of protamines I and II (MW approximately 11,000 daltons and 7,000 daltons, respectively) is approximately 0.4 microM. Protamine II (MW approximately 4,800 daltons) was equally active (half maximum inhibition concentration approximately 0.4 microM); protamine IV (MW approximately 3,300 daltons) was substantially less active (half maximum inhibition concentration approximately 2.8 microM). These investigations have extended previous observations that protamine sulfate is a potent inhibitor of PDGF binding and establish that protamine sulfate blocks PDGF binding at the physiological receptor, preventing PDGF initiated biological activities. Protamine sulfate can be used as a reagent to separate the influence of PDGF and EGF on cells with high specificity and has been used to demonstrate that the receptors on simian sarcoma virus transformed 3T3 cells qualitatively respond identically to protamine sulfate as to unlabelled PDGF and are likely identical to those on nontransformed 3T3 cells.

Expression of a platelet-derived growth factor-like protein in simian sarcoma virus transformed cells

The near identity of the partial amino acid sequence of human platelet-derived growth factor (PDGF) and that predicted for p28sis, the putative transforming protein of the simian sarcoma virus (SSV), suggests expression of a growth factor activity may be central for transformation by SSV. It is now reported that SSV-transformed cells but not control cells contain a growth factor activity that is identical to PDGF in immunoassay, in mitogenic dose response, and in specific mitogenic activity. The protein immunoprecipitated by antiserum to human PDGF has an apparent molecular weight of 20,000, identical to that of p20sis, the putative intracellular degradation product of p28sis. The results support the concept that expression of a PDGF-like molecule, which appears to be the product of the viral-sis gene, is responsible for the abnormal regulation of growth is SSV-transformed cells.