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H L Cooper

Publications and source records attributed to H L Cooper.

At least 37 records · Page 2Linked to original sources
PubMed1987

Proteins associated with B lymphocyte hyperactivity in New Zealand black mice.

New Zealand Black (NZB) mice exhibit polyclonal B cell activation and elevated immunoglobulin production, an abnormality associated with the spontaneous autoimmune disease that affects this strain. To further our understanding of this abnormality of B cell differentiation and maturation, we have employed two-dimensional polyacrylamide gel electrophoresis to analyze the proteins synthesized by lymphocytes of several strains. Two proteins were produced by lymphocytes from NZB mice but not those from normal strains. One was a 16 kd protein with a pI of 5.1, and the other was a 27.5 kd protein with a pI of 4.5. The presence of the xid gene on the NZB background suppressed production of both proteins. They were synthesized by spleen cells but not by bone marrow or lymph node cells, and production was restricted to enlarged B lymphocytes. p16 was synthesized by normal mouse strain B cells upon stimulation with LPS. The 27.5 kd protein was shown to be secreted. On the basis of partial amino acid sequence determination of proteins eluted from gels, p27.5 was identified as J chain and p16 as the C terminal fragment of mu-chain. The synthesis of two other proteins, 13 kd and 18 kd in size, was elevated in NZB spleen lymphocytes. The 18 kd protein was identified as translation initiation factor eIf-4D. The increased level of this protein may be related to the upregulation of immunoglobulin synthesis.

Amino Acid Sequence↗
PubMed1986

Identification and characterization of the nonphosphorylated precursor of pp17, a phosphoprotein associated with phorbol ester induction of growth arrest and monocytic differentiation in HL-60 promyelocytic leukemia cells.

Treatment of HL-60 promyelocytic leukemia cells with the tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), causes rapid phosphorylation and dephosphorylation of pp17, a 17-20-kDa, pI 5.5 cytosolic protein, as an early event in a response sequence leading to growth arrest and terminal differentiation into monocytes (Feuerstein, N., and Cooper, H. L., (1984) J. Biol. Chem. 259, 2782-2788). In the present study, we have identified the nonphosphorylated precursor to pp17 by tryptic peptide mapping of single proteins recovered from two-dimensional gels. The pI of the precursor, p17, was 5.9, and the apparent Mr of both p17 and pp17 was 18,400 by SDS-polyacrylamide gel electrophoresis (one dimension). p17 was shown to be a major cytosolic protein, comprising about 0.5% of steady state labeled protein in that fraction. Both p17 and pp17 were found exclusively in the cytosol (detergent-released SOL) and were not detected in membranes, cytoskeleton, or nuclei. In untreated cells, about 90% of the protein was present in the nonphosphorylated form. Upon TPA treatment, pre-existing p17 was rapidly phosphorylated to pp17. After 15 min, the two forms were nearly equal in quantity. This corresponds to phosphorylation, within that period, of about 0.2% of total cytosolic protein, represented by a single species. The maximum level of pp17 was reached within 1 h, with pp17 exceeding p17 by about 25%. Quantitatively, therefore, the phosphorylation of p17 to pp17 is one of the most prominent early biochemical responses to TPA treatment. Available data indicate that p17 predominates in rapidly proliferating cells, while phosphorylation to pp17 occurs where cell growth is modified by TPA or other agents. Thus, the p17/pp17 system is potentially a major mechanism for intracellular propagation of growth regulatory signals. We propose the name, prosolin, for this prominent cytosolic protein.

Carrier Proteins↗
PubMed1986

Analysis of ras oncogene products by two-dimensional gel electrophoresis: evidence for protein families with distinctive molecular forms.

Protein products of the ras family of oncogenes were immunoprecipitated by an anti-p21 monoclonal antibody, separated by two-dimensional gel electrophoresis and subsequently detected by western immunoblot analysis using the same anti-p21 monoclonal antibody as a probe. Using this method, a 21 kDa oncogene protein (p21) was detected and characterized in cell lines containing Harvey (Ha), Kirsten (Ki), neuroblastoma (N), or cellular (proto) ras genes. The ras gene products from all cell types occurred with multiple forms differing in size, charge or in both parameters. Transforming ras oncogene proteins occurred in easily identifiable groups that were different from each other in molecular weight and charge, were distinctive for each ras gene type and were different from cellular ras equivalents. Similar, but not identical, family groups occurred in different cell types containing the same oncogene. The reproducible occurrence of unpredicted p21 forms suggests that previously unreported post-translational processing steps may be associated with the synthesis of certain oncogene products. This immunoprecipitation/two-dimensional gel/western blot technique is a simple method for the identification and characterization of p21 gene products.

Amino Acid Sequence↗
PubMed1986

Effect of epidermal growth factor and 12-O-tetradecanoylphorbol-13-acetate on the phosphorylation of soluble acidic proteins in A431 epidermoid carcinoma cells.

Treatment of [32P]phosphate prelabeled intact human A431 epidermoid carcinoma cells with epidermal growth factor (EGF, 100 ng/ml) or 12-O-tetradecanoylphorbol-13-acetate (TPA, 10(-7)M) resulted in a selective enhancement in the phosphorylation of the following soluble acidic proteins: a phosphoprotein with a molecular weight of 17,000 (pp17; similar notation used throughout) pI approximately 5.5); pp27 (pI approximately 5.5); pp34 (pI approximately 6.2); and pp80 (pI approximately 4.5) as detected by two-dimensional gel electrophoresis. EGF or TPA induced a 4- to 6-fold increase in the phosphorylation of pp17 and a 2- to 4-fold increase in the phosphorylation of pp27, pp34, and pp80 within 15 min after treatment of subconfluent A431 cells. Alkali treatment of the gels removed most of the incorporated [32P] phosphate from the phosphoproteins, including pp27, pp34, and pp80; however, the phosphoester bond in pp17 was stable to alkaline hydrolysis since there was no removal of [32P]phosphate from this protein. Treatment of A431 cells with dibutyryl cyclic adenosine 3':5'-monophosphate (1 mM) also increased the phosphorylation of pp17, pp27, and pp34 but not of pp80. Activation of endogenous calcium- and phospholipid-dependent protein kinase C in the cytosol of A431 cells in a cell-free system resulted in the enhanced phosphorylation of pp27, pp34, and pp80 but not of pp17 while exogenous addition of the catalytic subunit of cyclic adenosine 3':5'-monophosphate-dependent protein kinase to cytosol preparations resulted in the phosphorylation of pp17, pp27, and pp34, but not of pp80. These results demonstrate that at least four soluble acidic proteins are phosphorylated in A431 cells in response to either EGF or TPA in vivo suggesting that these two agents may exert part of their biological effects on A431 cells through a biochemical pathway involving the phosphorylation of several common proteins; moreover, the studies suggest that these four acidic proteins may be substrates in vitro for protein kinase C and/or a cyclic adenosine 3':5'-monophosphate-dependent protein kinase.

Bucladesine↗
PubMed1985

Lymphocyte blastogenesis. Post-transcriptional controls of protein synthesis.

To better understand the regulation of macromolecular synthesis in the response of lymphocytes to a mitogen, we have used two-dimensional electrophoresis to search for specificity in the early increase seen in protein synthesis in human lymphocytes treated with phytohemagglutinin and examined the role of new RNA synthesis in this response. Our results confirm a major increase in overall protein synthesis after 4 h of phytohemagglutinin treatment. A further disproportionate increase in the synthetic rates of certain polypeptides was observed using two-dimensional polyacrylamide gel electrophoresis. While actinomycin-D reduced protein synthesis to a level below that of untreated cells, phytohemagglutinin nonetheless enhanced total protein synthesis even in the presence of actinomycin. Some, but not all, of the disproportionate increases in synthesis seen for certain polypeptides are blocked by actinomycin. These results imply the existence of multiple mechanisms controlling protein synthesis early in the course of lymphocyte stimulation. At least some of these do not require new RNA synthesis and thus operate at a post-transcriptional level.

Blood Proteins↗
PubMed1985

Phorbol ester effect in platelets, lymphocytes, and leukemic cells (HL-60) is associated with enhanced phosphorylation of class I HLA antigens. Coprecipitation of myosin light chain.

Phorbol-12-myristate-13-acetate (PMA) is a potent tumor promoter. However, the mechanism of its effect is still unknown. In the present study we use two dimensional gel electrophoresis to show that the PMA effect on platelets is associated with enhanced phosphorylation of a series of polypeptides at 44K which migrate close to but distinct from a previously reported 47K protein. We identified these proteins as the class I molecules of the human histocompatibility antigens (HLA A,B). We further demonstrate that the PMA effect is also associated with a dramatic phosphorylation of HLA antigens in HL-60 leukemic cells and in human lymphocytes, showing that an increase in phosphorylation of HLA antigens is intimately related to the signal of PMA in various cellular systems. Immunoprecipitation of HLA proteins resulted in coprecipitation of phosphorylated myosin light chain (20K). HLA antigens are transmembrane proteins which interact with cytoskeletal elements, probably via their intracellular region, which has been previously shown to be phosphorylated. It is suggested that phosphorylation of HLA membrane proteins may represent an important mechanism in the effects induced by PMA.

Blood Platelets↗
PubMed1985

Suppression of tropomyosin synthesis, a common biochemical feature of oncogenesis by structurally diverse retroviral oncogenes.

To identify proteins whose production may be altered as a common event in the expression of structurally diverse oncogenes, we compared two-dimensional electropherograms of newly synthesized proteins from NIH/3T3 cell lines transformed by a variety of retroviral oncogenes, from cellular revertant lines, and from a line (433.3) which expresses the v-ras oncogene in response to corticosteroids. Most alterations in the synthesis of specific proteins detected by this approach appeared to be the result of selection during prolonged cultivation and were probably unrelated to the transformation process. However, we detected seven proteins whose synthesis was strongly suppressed in cell lines transformed by each of the six retroviral oncogenes we studied and whose production was fully or partially restored in two cellular revertant lines. Suppression of two of these proteins was also correlated with the initial appearance of morphological alteration during corticosteroid-induced oncogene expression in 433.3 cells. These proteins (p37/4.78 and p41/4.75) were identified as tropomyosins, a group of at least five cytoskeletal proteins. Transformation by the papovaviruses simian virus 40 and polyomavirus caused no suppression of synthesis of these tropomyosins. This indicates that suppression of tropomyosin synthesis is not a nonspecific response by cells to being forced to grow with the transformed phenotype but is specifically associated with oncogenesis by diverse retroviral oncogenes. The results are consistent with the hypothesis that the different biochemical processes initiated by expression of structurally diverse retroviral oncogenes may converge on a limited number of common targets, one of which is the mechanism which regulates the synthesis of tropomyosins.

Animals↗
PubMed1985

Cell-free system studies on the phosphorylation of the 17,000-20,000 dalton protein induced by phorbol ester in human leukemic cells and evidence for a similar event in virally transformed murine fibroblasts.

We have shown previously that a prominent early signal in the phorbol-12-myristate-13-acetate (PMA) effect on leukemic cells as well as on other malignant cells is a rapid and dramatic increase in the turnover of phosphate in a Mr 17,000 to 20,000 cytosolic protein and a moderate increase in turnover of phosphate in a Mr 27,000 protein, as detected in the intact cells by 2-dimensional gel electrophoresis. To further elucidate the mechanism of this phosphorylation event, we have examined the protein kinases which can reconstitute this event in a cell-free system. Activation of the endogenous Ca2+-activated phospholipid-dependent protein kinase (Ca-PL-PK) as well as addition of purified Ca-PL-PK to the cytosol of HL-60 leukemic cells resulted in enhanced phosphorylation of phosphoprotein Mr 27,000 (PP27) but did not affect the phosphorylation of phosphoprotein Mr 17,000 to 20,000 (PP17-20). In contrast, PP17-20 was heavily phosphorylated under cell-free conditions by the catalytic subunit of cAMP-dependent protein kinase (cAMP-PK). Exposure of intact cells to dibutyryl-cAMP resulted in increased phosphorylation of PP17-20. These conditions also enhanced the phosphorylation of PP27, showing that PP27 can act as a substrate for both Ca-PL-PK and cAMP-PK under cell-free conditions. Tryptic digest analysis of PP17-20 showed that one of four phosphopeptides is preferentially phosphorylated in PMA-induced PP17-20. An additional phosphopeptide was phosphorylated in cAMP-PK-catalyzed PP17-20. Thus, cAMP-PK alone mimics the effect of PMA on phosphorylation of PP17-20, but it introduces additional modifications. The precise role of this kinase in PMA-induced phosphorylation of PP17-20 remains to be clarified. We found further that enhanced phosphorylation of PP17-20 is also associated with malignant transformation of NIH/3T3 cells transformed by V-rasKi oncogene of Kirsten sarcoma virus. The tryptic phosphopeptide map of PP17-20 (phosphorylated in vivo) in the transformed cells was similar to that of PP17-20 in PMA-treated HL-60 cells but not to that induced by cAMP-PK, suggesting that the process activated by PMA which leads to phosphorylation of PP17-20 resembles an intrinsic cellular process which is enhanced in certain malignant cells.

Animals↗
PubMed1985

Analysis of lymphocyte proteins from New Zealand black mice by two-dimensional gel electrophoresis.

Splenic lymphocyte proteins from New Zealand Black (NZB) mice, which spontaneously develop autoimmune disease, and several control strains were analyzed by two-dimensional polyacrylamide gel electrophoresis. A number of strain- and age-related differences were observed, among which was the persistently elevated synthesis of two peptides, 12.5 KD and 10.5 KD, by spleen cells from older NZB mice. Although synthesis of these peptides was moderately high in young NZB and control mice, it diminished with age in control mice. These proteins were found in the cytoplasm and were not expressed on the plasma membrane nor secreted into the medium. Production of these proteins was restricted to B and null cells; T cells did not synthesize these peptides. These proteins appear to be indicators of disease activity, because their increased synthesis was associated with lymphocyte subset alterations associated with the onset of overt autoimmune disease in NZB mice.

Aging↗
PubMed1984

Purification of human interleukin 2 to apparent homogeneity and partial characterization of its receptor.

Human interleukin 2, produced by phytohemagglutinin-stimulated peripheral blood lymphocytes cultured in the absence of serum, has been purified to apparent homogeneity with a two-step combination of affinity chromatography with Cibacron blue-Sepharose and gel filtration. The specific activity of the purified IL-2 was 620,000 U/mg of protein, with a total recovery of approximately 13% biological activity. Purified IL-2 stimulated lymphocyte proliferation at a concentration of 4.3 X 10(-10) M. IL-2 was radiolabeled with reductive methylation to a specific activity of 350 microCi/nmol. Binding studies with phytohemagglutinin-activated lymphocytes, known to express receptor for IL-2, identified a single population of approximately 21,000 receptors per cell with an equilibrium dissociation constant of 7.1 X 10(-10) M.

Autoradiography↗
PubMed1984

The mammalian hypusine-containing protein, eukaryotic initiation factor 4D. Structural homology of this protein from several species.

A single cellular protein of Mr approximately 18,000 and pI near 5.1, recently identified as eukaryotic translation initiation factor eIF-4D, contains the unusual amino acid hypusine [N epsilon-(4-amino--2-hydroxybutyl)lysine] formed post-translationally from lysine with a structural contribution from the polyamine spermidine. When the 3H-labeled hypusine-containing protein isolated from Chinese hamster ovary (CHO) cells that were grown with radioactive polyamine is digested with trypsin and the digest is subjected to two-dimensional separation, a single radioactive peptide is seen. A labeled peptide that occupies this same position is found in a digest of the [3H]hypusine protein from human lymphocytes and the single hypusine-containing tryptic peptide from purified rabbit reticulocyte eIF-4D also moves to this identical position. Stepwise Edman degradation of the tryptic digest of CHO cell hypusine-protein releases the radioactivity as a single peak in accordance with our earlier evidence for a single hypusine residue per molecule of eIF-4D. The similar patterns of radioactive peptides obtained from tryptic digests of radioiodinated eIF-4D from CHO cells, human lymphocytes, and rabbit reticulocytes suggest a highly conserved primary structure for this protein.

Animals↗
PubMed1984

Studies of the differentiation of promyelocytic cells by phorbol ester. I. Induction of discrete membrane proteins characteristic of monocytes and expression of motility functions in HL-60 cells following differentiation by phorbol ester.

Cells of the promyelocytic leukemia line, HL-60, differentiate into macrophage-like cells in response to phorbol ester. We report that this effect is associated with induction of spontaneous motility and a modest expression of chemotactic responsiveness to a formylated peptide. Using two-dimensional gel electrophoresis we demonstrate that the differentiation of HL-60 cells is associated with a differential effect on membrane vs. cytosol proteins. Changes in the cytosol characteristically involved reduction of synthesis of specific proteins. Changes in the membrane were mainly associated with either enhancement or de novo synthesis of discrete proteins. The hallmark of HL-60 cell differentiation appeared to be distinctive induction of a membrane-bound group of six proteins (pI approximately equal to 5, 45-70 kDa) and the de novo induction of a membrane protein indicated as m10 (pI approximately equal to 7, 28 kDa). These discrete membrane proteins were found to be very prominently synthesized by human cultured monocytes, but virtually absent in lymphocytes. It is proposed that our ability to detect synthesis of proteins characteristic of different states of cellular differentiation will permit detailed studies of the biochemical changes which constitute this process. Definition of the role of these proteins and the mechanism regulating their synthesis will help to elucidate the biochemical basis of monocyte differentiation.

Cell Differentiation↗
PubMed1984

Studies of the differentiation of promyelocytic cells by phorbol ester. II. A methylation inhibitor, 3-deazaadenosine, inhibits the induction of specific differentiation proteins. Lack of effect on early and late phosphorylation events.

Cells of the promyelocytic leukemic line, HL-60, differentiate into macrophage-like cells in response to phorbol-12-myristate-13-acetate (phorbol ester). We have shown that this process is associated with expression of motility functions and induction of specific changes in the synthesis of discrete proteins. In the present study we show that a methylation inhibitor, 3-deazaadenosine, inhibits the phorbol ester induction of the differentiation functions, adherence and motility. These effects were associated with interference in the expression of membrane proteins indicative of the acquisition of macrophage-like characteristics by HL-60 cells. Of particular importance was the observation that the methylation inhibitor preferentially arrested the induction of one differentiation, protein m10 (pI approximately equal to 7, 28 kDa). The selective effect of 3-deazaadenosine is further supported by observations in this study which show that the methylation inhibitor did not affect other cellular and biochemical effects of phorbol ester in these cells. Most significantly, 3-deazaadenosine did not inhibit the induction of phosphorylation in pp17 and pp27, which was previously shown to be a rapid event associated with initiation of differentiation in HL-60 cells by phorbol ester (Feuerstein, N. and Cooper, H. (1983) J. Biol. Chem. 258, 10786-10793). Furthermore, later elevated phosphorylation of other proteins as well as the arrest of cell growth induced by phorbol ester were also unimpeded by the methylation inhibitor. These results indicate that the methylation inhibitor did not interfere with the transduction of the phorbol ester signal at an early step so as to block all the subsequent events in this sequence, but rather its effect was selectively associated with interference in later events in the sequence of differentiation. It is proposed that transmethylation events might be specifically involved in the induction and expression of discrete proteins during the differentiation of these leukemic cells but not in the initial propagation of the signal produced by phorbol ester binding.

Cell Adhesion↗
PubMed1984

Rapid phosphorylation-dephosphorylation of specific proteins induced by phorbol ester in HL-60 cells. Further characterization of the phosphorylation of 17-kilodalton and 27-kilodalton proteins in myeloid leukemic cells and human monocytes.

Treatment of the promyelocytic leukemic cells, HL-60, with phorbol-12-myristate-13-acetate (PMA) results in arrest of growth and terminal differentiation of the cells into macrophages. We have reported that within minutes following exposure of these cells to PMA there is an increase of severalfold in phosphorylation of two cytosol proteins: 17-20 kDa (pp17, pI approximately 5.5) and 27 kDa (pp27, pI approximately 5.5) as detected in the intact cells by two-dimensional gel electrophoresis. In this report, by analyzing the chase kinetics of 32Pi in cellular proteins, we show that PMA treatment induces a rapid and specific loss of 32Pi from pp17 and pp27. Comparison with kinetics of [3H]leucine loss from these proteins indicates that this effect is due to induction by PMA of rapid turnover of phosphate in pp17 and pp27. This activity persisted in HL-60 for at least 24 h and was also seen in two other cell types studied (U937 leukemia and normal monocytes). The Ca2+ channel blocker, nifedipine, had no effect on PMA-induced 32Pi turnover in pp17, while trifluoroperazine, which is known to inhibit protein kinase C, blocked these events and also inhibited other cellular effects of PMA (adherence and growth arrest). Thus, induction of rapid 32Pi turnover in pp17 and pp27 may be an essential early signal in initiating and maintaining cellular effects of PMA. Myosin light chain (20 kDa), another phosphorylated protein, was shown to be not identical with pp17, although of similar Mr.

Cell Line↗
PubMed1984

Glycogen regulation in LPS-stimulated murine splenocytes.

Enzymatic glycogen regulation in mouse splenocytes cultured in vitro with and without LPS, was studied from 0-72 h. Increased [3H]glucose uptake and hexokinase activity demonstrated the activation of cells treated with LPS. There was a greater time-dependent increase of cellular glycogen content in LPS-stimulated cells as compared to control. Glycogen synthetase I in LPS-stimulated cells increased about 200% above control cells to a plateau at 48 h, while in unstimulated cells there was little increase throughout. Glycogen synthetase D increased continually to 72 h in both groups. In the stimulated cells, phosphorylase increased only 90% above control cells up to 48 h. It was concluded that the increased glycogen content of LPS-stimulated cells seen at 48 h may result from an increase in both glycogen synthetase I and D activity compared to lesser increase in hydrolysis. However, between 48 and 72 h, the period of RNA and DNA increased synthesis, the glycogen content of stimulated cells did not increase further, consistent with the observation that synthetase I activity remained constant and synthetase D decreased. Thus, following mitogenic stimulation, the net effect of the enzymatic regulation is to increase cellular glycogen, as an energy source for subsequent events.

Animals↗
PubMed1984

Comparison of structural and functional variation in class I HLA molecules: the role of charged amino acid substitutions.

Functional and structural heterogeneity of HLA class I molecules was sought among five donors serologically identical for A2, A3, B7, and Bw44. Functional differences were identified by cell-mediated lympholysis (CML) after allogeneic mixed lymphocyte reaction among the five donors. Structural differences were characterized by high resolution two-dimensional electrophoretic maps of the class I HLA proteins synthesized by peripheral blood lymphocytes of these donors. Cells from three donors showed no CML-defined differences from one another; their HLA protein maps were identical. The cells of one donor recognized an A3-associated target antigen on the cells of all the other donors; her HLA map revealed a unique protein with altered isoelectric point. Another donor's cells differed by two CML-detected antigens: one was identified as a variant of Bw44 ("44.2") and the other was associated with Cw4. This donor's two-dimensional HLA map showed two novel charged proteins. By using these data, a two-dimensional map locating HLA-A2, -A3, -A3', -B7, -Bw44.1, -Bw44.2, and -Cw4 was prepared. Because each of three CML-detected antigens was correlated with a protein of distinctive charge, our results and the available published data raise the possibility that amino acid substitution producing charge variation may be a particularly important mechanism in the generation of CML-detectable HLA diversity.

Amino Acids↗
PubMed1984

Differential phosphorylation events associated with phorbol ester effects on acceleration versus inhibition of cell growth.

Phorbol-12-myristate-13-acetate (PMA) in some systems causes inhibition of growth; in others, PMA exerts a mitogenic effect. We have previously reported that the PMA-induced growth arrest and differentiation in leukemic cells are associated with a rapid increase in phosphorylation-dephosphorylation of two cytosolic proteins, phosphoprotein with molecular weights of 17,000 to 20,000 (pp 17-20) and phosphoprotein with a molecular weight of 27,000 (pla approximately 5.5). The phosphorylation of these proteins was found to be catalyzed directly by cyclic adenosine 3':5'-monophosphate-dependent protein kinase. To elucidate whether these phosphorylation events are specific to certain cellular functions induced by PMA, we compared the effect of PMA on phosphorylation of proteins in several cell systems. We found that, in cells where PMA accelerates growth (NIH/3T3 mouse fibroblasts, JB-6 mouse epidermal cells, and human peripheral lymphocytes) as well as in human platelets, the phosphorylation of pp 17-20 was only slightly affected by PMA, while phosphorylation of other proteins at Mr approximately 80,000 (pl approximately 5) and Mr 20,000 (pl approximately 5.2) was markedly increased. We provide evidence to suggest that the Mr 20,000/pl 5.2 protein might be myosin light chain (Mr 20,000). In contrast to these cell systems, in the human malignant cell A431 epidermoid carcinoma, the growth of which is inhibited by PMA, the pattern of protein phosphorylation by PMA exhibited striking similarity to that of leukemic cells; phosphorylation of pp 17-20 was dramatically increased while the phosphorylation of the putative myosin light chain (Mr 20,000/pl 5.2) was not affected. The identity of pp 17-20 in A431 and HL-60 leukemic cells was demonstrated by the unique stability of its phosphoester bond to alkali treatment. These results suggest that phosphorylation of different proteins and possibly activation of different protein kinases mediate the effects of PMA on inhibition versus acceleration of growth. Specifically, phosphorylation-dephosphorylation of pp 17-20 emerges as a signal which might be preferentially involved in PMA effect in certain neoplastic cells.

Animals↗