PubMed Health⌕ Search

Biomedical subjects

J F Mushinski

Publications and source records attributed to J F Mushinski.

At least 55 records · Page 3Linked to original sources

Phorbol ester-induced myeloid differentiation is mediated by protein kinase C-alpha and -delta and not by protein kinase C-beta II, -epsilon, -zeta, and -eta.

It is generally accepted that the multiple, similar protein kinase C (PKC) isozymes are responsible for different specialized physiological processes, but evidence that directly assigns specific functions to specific isozymes is scarce. To test whether specific PKC isozymes are involved in myeloid differentiation, we have studied the effect of overexpression of PKC-alpha, -beta II, -delta, -epsilon, -zeta and -eta in 32D, a mouse myeloid progenitor cell line that does not differentiate in response to 12-O-tetradecanoylphorbol-13-acetate (TPA). No significant morphological or phenotypic changes could be observed in unstimulated cells that overexpress any of these isozymes. However, the cell lines that overexpressed PKC-alpha or -delta had acquired the ability to become mature macrophages 2-6 h after TPA stimulation. The overexpression of PKC-beta II, -epsilon, -zeta, or -eta, in contrast, did not permit TPA-induced differentiation. These results indicate that only these two members of the PKC gene family can participate in TPA-induced myeloid differentiation.

Animals↗

Unique expression pattern of protein kinase C-theta: high mRNA levels in normal mouse testes and in T-lymphocytic cells and neoplasms.

A 2.2-kb cDNA that contains the entire coding region of mouse protein kinase C-theta (PKC-theta) was cloned from skeletal muscle mRNA using reverse transcription and the polymerase chain reaction (PCR). This clone was used as a probe to study the expression of this PKC isoform in normal and transformed hemopoietic cells and other normal tissues. By far the highest steady-state level of PKC-theta mRNA was found as a 2.8-kb transcript on a Northern blot of poly(A)+ RNA from testes. High levels were also found in skeletal muscle, spleen, T lymphomas and purified normal T lymphocytes, but these tissues and cells expressed two transcripts, 3.3 kb and 3.8 kb. Lower levels of similar size transcripts were found in normal brain, B lymphocytes and B-lymphocytic tumors and cell lines.

Animals↗

Overexpression of protein kinase C-delta and -epsilon in NIH 3T3 cells induces opposite effects on growth, morphology, anchorage dependence, and tumorigenicity.

We have determined the patterns of mRNA and protein expression of 7 protein kinase C (PKC) isozymes in NIH 3T3 cells. Only PKC-alpha is expressed abundantly in NIH 3T3 cells; endogenous levels of the other 6 PKC isozymes are low or undetectable. We have overexpressed PKC-delta and -epsilon in these cells to observe activation/translocation of these two isozymes and the biological consequences of overexpression. Both PKC-delta and -epsilon, but not PKC-alpha, are partially associated with the insoluble fraction even in the absence of phorbol 12-myristate 13-acetate (PMA). Upon PMA stimulation, both PKC-delta and -epsilon translocate to the insoluble fraction of cell homogenates, as can be observed with the endogenous PKC-alpha. Overexpression of PKC-delta induces significant changes in morphology and causes the cells to grow more slowly and to a decreased cell density in confluent cultures. These changes are accentuated by treatment with PMA. Overexpression of PKC-epsilon does not lead to morphological changes, but causes increased growth rates and higher cell densities in monolayers. None of the PKC-delta overexpressers grow in soft agar with or without PMA, but all the cell lines that overexpress PKC-epsilon grow in soft agar in the absence of PMA, but not in its presence. NIH 3T3 cells that overexpress PKC-epsilon also form tumors in nude mice with 100% incidence. This indicates that high expression of PKC-epsilon contributes to neoplastic transformation.

3T3 Cells↗

Molecular analysis of double isotype expression in IgA switching.

In this and previous studies we have shown that during the course of B cell isotype differentiation occurring in the CH12.LX B cell line, small numbers of cells appear that bear both membrane (m)IgM and membrane IgA. We have cloned relatively stable populations of such dual-bearing cells and have performed studies to determine their molecular status. In the study of one such subclone (CH12.LX.7.10), we show by primer extension that both mu and alpha mRNA contain identical VHDJH gene segments. In complementary studies of another such subclone (CH12.LX.7.13), we show using DNA restriction fragment analysis, that the C mu gene segment, but not the C alpha gene segment, is associated with the JH gene segment. Additionally, Northern blot analysis of productive message of this clone shows that both mu and alpha mRNA cohybridize to the same VH region-specific probe. Taken together, these data suggest that CH12.LX mIgM/mIgA dual-bearing cells occur in the absence of C mu gene segment deletion and that the mu and alpha mRNA transcripts are derived using an alternative mechanism such as transplicing or alternative splicing of a long RNA transcript. On the assumption that these clones are representative of mIgM/mIgA dual-bearing cells appearing during CH12.LX IgM to IgA isotype differentiation, these data support the idea that B cells simultaneously produce mu and alpha mRNA transcripts during one stage of IgA isotype switching.

Animals↗

Co-amplification of c-myc/pvt-1 in immortalized mouse B-lymphocytic cell lines results in a novel pvt-1/AJ-1 transcript.

In a series of mouse pvt-1 cDNA clones prepared from an immortalized B-cell line that contains an amplified c-myc/pvt-1 region, we have identified a unique cDNA, AJ-I, which contains 57 bp of pvt-1 sequence (pvt-1a) spliced to a novel sequence of 2.1 kb. We report here that this 3' segment (termed AJ-IX) maps more than 60 kb telomeric to pvt-1a and is encoded by a novel locus (AJ-I) on mouse chromosome 15. The AJ-IX probe detects a transcript that is expressed only in normal mouse brain and testis. Several mast-cell tumors, Ly-I+ B-lymphocytic cell lines and a neuroblastoma also display abundant levels of AJ-IX-specific mRNA. However, splicing of pvt-1a to AJ-IX is found exclusively in Ly-I+ B-cell lines that contain amplified c-myc/pvt-1. We conclude that some features in the generation of this amplicon facilitates the synthesis of a pvt-1/AJ-IX chimeric mRNA that may play a role in immortalization of these Ly-I+ B-cell lines.

Animals↗

Ca(2+)-dependent and Ca(2+)-independent isozymes of protein kinase C mediate exocytosis in antigen-stimulated rat basophilic RBL-2H3 cells. Reconstitution of secretory responses with Ca2+ and purified isozymes in washed permeabilized cells.

Rat basophilic RBL-2H3 cells, which exhibit Ca(2+)-dependent secretion of granules when stimulated with antigen, contained the Ca(2+)-dependent alpha and beta and the Ca(2+)-independent delta, epsilon, and zeta isoforms of protein kinase C. These isoforms associated, to variable extents (i.e. delta the most and zeta the least), with the membrane fraction upon antigen stimulation but without external Ca2+; only the Ca(2+)-independent isoforms did so. Both types of isozymes were probably necessary for optimal responses to antigen as indicated by the following observations. All Ca(2+)-dependent isozymes were degraded in cells treated with 20 nM phorbol 12-myristate 13-acetate for 6 h, whereas the Ca(2+)-independent isozymes were not degraded and were retained when the cells were subsequently permeabilized and washed. Cells so treated still exhibited antigen-induced secretion (25-33% of normal) which was suppressed by selective inhibitors of protein kinase C (Ro31-7549 and calphostin C) thereby indicating a possible contribution of the Ca(2+)-independent isozymes in secretion. Normally, washed permeabilized cells lost all isozymes of protein kinase C and failed to secrete in response to antigen. A full secretory response to antigen could be reconstituted by the subsequent addition of nanomolar concentrations of either beta or delta isozymes of protein kinase C (other isozymes were much less effective) but only in the presence of 1 microM free Ca2+ to indicate distinct roles for Ca2+ and protein kinase C in exocytosis.

Animals↗

Addition of constitutive c-myc expression to Abelson murine leukemia virus changes the phenotype of the cells transformed by the virus from pre-B-cell lymphomas to plasmacytomas.

Abelson murine leukemia virus (A-MuLV), a retrovirus that expresses the v-abl oncogene, characteristically induces pre-B-cell lymphomas following in vivo infection of BALB/c mice or in vitro infection of suspensions of fetal liver or bone marrow cells. ABL-MYC, a retrovirus that expresses both v-abl and c-myc, induces solely plasmacytomas in BALB/c mice. To investigate how the addition of overexpression of c-myc to that of v-abl accomplishes this dramatic change in the phenotype of the cells transformed by these closely related retroviruses, we utilized helper-free A-MuLV (psi 2) and ABL-MYC (psi 2) in vitro to infect suspensions of cells from different lymphoid tissues and purified immature and purified mature B cells. As expected, A-MuLV(psi 2) induced only pre-B-cell lymphomas in vivo and in vitro when immature B cells were present. ABL-MYC(psi 2), on the other hand, produced only plasmacytomas, even when purified immature B lymphocytes were infected in vitro. Although the A-MuLV(psi 2)-induced pre-B-cell lymphomas express easily detectable levels of c-myc mRNA, maturation into more-mature forms of B lymphocytes is blocked. The constitutively overexpressed c-myc in the ABL-MYC retrovirus abrogates this block, permits maturation of infected immature B cells, and yields transformed plasma cells.

Abelson murine leukemia virus↗

Characterization of ligand and substrate specificity for the calcium-dependent and calcium-independent protein kinase C isozymes.

Analysis of [3H]phorbol-12,13-dibutyrate (PDBu) binding was performed with protein kinase C (PKC)-alpha, -beta 1, -gamma, -delta, -epsilon, -eta, and -zeta produced in Sf9 insect cells using the baculovirus expression system. With the exception of PKC-zeta, all of the PKC isozymes bound [3H]PDBu with high affinity (Kd < 1 nM), either in the presence or in the absence of calcium. Scatchard analysis using 100% phosphatidylserine vesicles revealed slightly lower affinity for the calcium-independent isozymes (PKC-delta, -epsilon, and -eta) than for the calcium-dependent isozymes (PKC-alpha, -beta, and -gamma). Competition for [3H]PDBu binding by different classes of PKC activators showed that 12-deoxyphorbol esters, mezerein, and octahydromezerein likewise possessed lower affinity for the calcium-independent isozymes. The mezerein analog thymeleatoxin was the most marked example, being almost 20-fold less potent for binding to PKC-epsilon and -eta than to PKC-beta 1. In contrast, the indole alkaloids (-)-indolactam V and (-)-octylindolactam V and the postulated endogenous activator 1,2-diacylglycerol bound with similar affinities to all of the PKC isoforms, suggesting that different residues/configurations in the binding sites of the different PKC isozymes might be involved in interaction with the pharmacophore of the activators. The seven PKC isozymes also showed clearly different substrate specificities with exogenous peptide and protein substrates. The heterogeneous behavior of the different members of the PKC family with ligands and substrates may contribute to the heterogeneity of PKC-mediated pathways at the cellular level.

Amino Acid Sequence↗

Retroviral enhancer insertion 5' of c-myc in two translocation-negative mouse plasmacytomas upregulates c-myc expression to different extents.

Essentially all murine plasmacytomas have deregulated c-myc expression that is typically brought about by chromosomal translocations between the c-myc/Pvt-1 locus and one of the immunoglobulin loci. ABPC 22 and RFPC 2782 are BALB/c plasmacytomas that lack chromosomal translocations yet have Southern blot evidence of c-myc gene rearrangements. In this report we show that proviral integrations 5' of the c-myc gene can deregulate c-myc expression in mouse plasmacytomas. Analysis of DNA sequences 5' of the c-myc genes from both tumors demonstrated that rearrangements were caused by retroviral integrations 5' of c-myc exon 1. The proviral insertion in RFPC 2782 was associated with a high steady-state c-myc mRNA level comparable to that seen in plasmacytomas with typical translocations. An analogous proviral insertion in ABPC 22 was associated with a c-myc RNA level that was only 38% of that of RFPC 2782. Nuclear run-on studies of c-myc transcription showed that ABPC 22 has both a lower rate of transcription and a greater degree of transcriptional attenuation than RFPC 2782. DNA sequencing of the long terminal repeat of each tumor provirus showed that the ABPC 22 provirus harbors a deletion of one of the two direct repeats in the viral enhancer, whereas both repeats are present in the RFPC 2782 provirus. These data indicate that maximum LTR enhancer effectiveness in plasmacytomas in vivo requires the presence of both LTR direct repeats. The documentation of the low level of steady-state c-myc mRNA in ABPC 22 supports the notion that deregulated c-myc expression, even at low steady state levels, is effective in supporting the development of plasmacytomas.

Animals↗

The cDNA sequence, expression pattern and protein characteristics of mouse protein kinase C-zeta.

A 2199-bp complementary DNA (cDNA) that encodes protein kinase C-zeta (PKC-zeta) has been isolated from mouse brain by a combination of reverse transcription and primer extension. The predicted PKC-zeta protein consists of 592 amino acids which are 99% identical to those of rat PKC-zeta. Northern blots that were probed with this cDNA revealed abundant 2200-nucleotide (nt) and 4200-nt PKC-zeta mRNAs in mouse brain in roughly equal amounts. PKC-zeta mRNA was also abundant in normal lung, kidney, and testes, and in several hemopoietic tumor lines. In all other mouse tissues and cell lines that were examined, at least faint levels of PKC-zeta mRNAs could also be detected. In tissues other than brain, the amount of PKC-zeta mRNA was less, and the smaller species generally predominated. Furthermore, in these tissues, both PKC-zeta mRNAs appear to be approximately 200 nt longer than the two mRNAs found in the brain. When the cDNA is expressed in insect cells via a baculovirus expression vector, a 75-kDa protein is synthesized which, unlike other PKC isoforms, does not bind phorbol ester, even at very high concentrations.

Amino Acid Sequence↗

Infrequent p53 mutation in mouse tumors with deregulated myc.

An invariant genetic lesion in mouse plasmacytomas is deregulated expression of c-myc as a consequence of chromosomal translocation. However, retroviral and transgenic studies suggest that additional genetic lesions may contribute to the genesis of plasmacytomas. The p53 tumor suppressor gene is a likely contributor to this genetic lesion, since there is a high incidence of p53 mutation in Burkitt's lymphomas and B-ALL (L3), both of which contain translocations involving c-myc analogous to those in plasmacytomas. In addition, p53 has been shown to be a transcriptional modulator of c-myc expression. In a survey of 27 mouse plasmacytomas by single-strand conformation polymorphism, we identified a single mutation (3.7% incidence), suggesting that p53 lesions are not frequent contributors to plasmacytomagenesis. A similar study of macrophage-monocyte tumors generated by a c-myc-containing retrovirus also indicates a lack of p53 involvement in deregulated c-myc expression. These results suggest that the specific maturation stage of transformed B-lymphocytes, independent of c-myc deregulation, may be the critical factor which determines the involvement of mutant p53.

Amino Acid Sequence↗

Transcripts encoding protein kinase C-alpha, -delta, -epsilon, -zeta, and -eta are expressed in basal and differentiating mouse keratinocytes in vitro and exhibit quantitative changes in neoplastic cells.

The protein kinase C (PKC) family of phospholipid-dependent serine-threonine kinases has been implicated in keratinocyte differentiation and neoplastic transformation. To determine if Ca(2+)-mediated keratinocyte differentiation is associated with changes in PKC isozyme gene expression, RNA was isolated from primary mouse keratinocytes grown in medium with 0.05, 0.12, or 1.4 mM Ca2+. Based on northern blot analysis, primary keratinocytes expressed mRNA encoding PKC-alpha, -delta, -epsilon, -zeta, and -eta, but not PKC-beta or -gamma. Relatively little change was detected in the level of these transcripts in cells induced to differentiate by exposure to elevated extracellular Ca2+. Interestingly, the PKC-zeta transcripts detected in RNA isolated from keratinocytes were approximately 200 nucleotides longer than those from mouse brain, suggesting the existence of an alternative form of this isozyme. An early change in benign neoplastic transformation of keratinocytes is the inability to differentiate in response to Ca2+ or the PKC activator 12-O-tetradecanoylphorbol-13-acetate, which is consistent with altered PKC function in these cells. The PKC isozyme mRNA profile was examined in two benign neoplastic keratinocyte cell lines, 308 and SP-1, which contain an activating mutation of the c-Ha-ras gene. Like normal keratinocytes. 308 and SP-1 cells expressed mRNA encoding PKC-alpha, -delta, -epsilon, -zeta, and -eta. However, the abundance of PKC-zeta transcripts in both cell lines was reduced by 74-89% when compared with normal keratinocytes at similar Ca2+ levels. In addition, SP-1 but not 308 cells exhibited a sevenfold increase in PKC-eta mRNA when cultured in medium with 1.4 mM Ca2+. To address whether these changes were related to the presence of an activated ras gene, RNA was isolated from primary keratinocytes transduced to a benign neoplastic phenotype with the v-Ha-ras oncogene. As with normal, 308, and SP-1 cells, v-Ha-ras keratinocytes expressed mRNA encoding PKC-alpha, -delta, -epsilon, -zeta and -eta. The level of PKC-zeta transcripts was similar in normal and v-Ha-ras keratinocytes, indicating that reduction of this mRNA in both 308 and SP-1 cells was not a direct result of ras activation. As in SP-1 cells, PKC-eta in v-Ha-ras keratinocytes was responsive to extracellular Ca2+, with a four-fold increase in transcript abundance in 0.12 mM Ca2+ medium relative to 0.05 mM Ca2+ medium.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Genes expressed selectively in plasmacytomas: markers of differentiation and transformation.

We have analyzed a murine plasmacytoma minus highly differentiated B lymphoma subtractive cDNA library and identified eight genes that are expressed in most plasmacytomas but at a much lower level, or not at all, in most B lymphomas. Four of the genes are markers of the terminal differentiation of B lymphocytes into plasma cells: placental alkaline phosphatase, also expressed in pre-B lymphomas xlr-3, a new X-linked member of the xlr multi-gene family EGP314, a pan-epithelial glycoprotein with sequence features of an adhesion molecule PC315, a gene that is up-regulated by IL6, but without obvious sequence homologies. Two of the genes are not clearly related to normal B cell differentiation, appearing to be associated with malignant transformation of plasma cells: PC326 is a new member of the beta-transducin mosaic protein gene family. It is an X-linked gene, expressed at a very low level in testis, but in no other normal tissue, including LPS- or IL6-induced plasma cells. It has a high level of expression (apparently dysregulated) in most (> 85%) mineral oil induced plasmacytomas. However the likelihood that PC326 is expressed decreases as the tumor latency decreases when different retroviral agents are used to accelerate mineral oil induced plasmacytomagenesis. This suggests that PC326 expression may be a late event in a multi-step process of tumorigenesis. PC251 a new member of the hematopoietic growth factor receptor family, most homologous to IL5R alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

Expression of murine cyclin B1 mRNAs and genetic mapping of related genomic sequences.

Two cDNAs that encode a protein with 87% identity to human cyclin B1 and that differ only in the length of their 3'-untranslated regions have been isolated from a 70Z/3B murine pre-B leukemia cell library. Three sizes of RNA transcripts were detected in Northern hybridization analyses of a variety of normal tissues and transformed cell lines using the cDNA inserts as probes. The expression of these RNAs can be modulated in tissue culture cell lines by physiologically relevant stimuli, increasing when cells are stimulated to proliferate and decreasing when cells are induced to differentiate. Moreover, RNAs from tissues that contain few proliferating cells have no detectable hybridizing transcripts. The coordinate regulation of these RNAs with other genes that are activated during the cell division cycle and the profound similarity of the predicted amino acid sequence to those of published cyclin B homologues indicate that these genes encode a murine cyclin B1. In Southern hybridization analysis of BALB/cAnPt genomic DNA digested with EcoRI, 12 fragments hybridized with the cDNA probes. Through Southern blot analyses of DNA from backcross and cogenic mice, recombinant inbred strains, and somatic cell hybrids, the genetic loci that produce the cyclin B1-related sequences (designated loci Cycb1-rs1 to Cycb1-rs9) were mapped on mouse chromosomes 5, 1, 17, 4, 14, 13, 7, X, and 8, respectively. Cycb1-rs6 (on chromosome 13) is discussed as the most likely candidate for an expressed structural gene locus.

3T3 Cells↗

A retrovirus that expresses v-abl and c-myc oncogenes rapidly induces plasmacytomas.

ABL-MYC, a murine retrovirus that encodes the v-abl and c-myc oncogenes, was constructed from Abelson murine leukemia virus (A-MuLV) in order to assess the biological consequences of co-expression of these genes in lymphoid cells. When inoculated into mice this retrovirus induced plasmacytomas in up to 100% of infected mice and less frequently induced pre-B lymphomas. Both tumor types contained genome-length proviruses in one or a few chromosomal locations, were mono- or oligoclonal as judged by immunoglobulin gene rearrangement and had unrearranged endogenous c-myc loci. The type of tumor induced depended upon the age and strain of mouse, and whether helper virus was present in the inoculated virus pool. ABL-MYC induced plasmacytomas with or without helper virus, with or without pretreatment of the mice with pristane, and in strains of mice resistant to pristane-induced plasmacytomas. Pristane treatment prior to ABL-MYC infection shortened the latent period of plasmacytomagenesis and produced mostly IgM-secreting tumors rather than IgA-secreting tumors, which predominantly arose in the absence of pristane. Control viruses for ABL-MYC with either a deletion in v-abl or a frameshift mutation in c-myc caused predominantly monocyte/macrophage tumors and pre-B-cell lymphomas respectively. Histopathological analysis of ABL-MYC-infected mice showed foci of transformed plasma cells as early as 14 days after infection. These results indicate that v-abl and c-myc act synergistically to transform mature B cells with high efficiency.

Animals↗

Expression of protein kinase C genes in hemopoietic cells is cell-type- and B cell-differentiation stage specific.

We have studied the expression of mRNA encoding all known protein kinase C (PKC) isozymes (alpha, beta, gamma, delta, epsilon, zeta, and eta) in murine tumor cell lines that exemplify hemopoietic cells arrested at different stages of development as well as in normal hemopoietic cells. We demonstrate that some of the isozymes, PKC-alpha, -beta, and -eta, are differentially expressed in different lineages. PKC-alpha and -beta generally are not detectable in myeloid cell lines, where PKC-delta is the predominant isoform. Both PKC-alpha and -beta are abundant in most T and B lymphocytic lines, but steady state levels of PKC-beta mRNA are lowest in plasma cell tumors, which exemplify the terminally differentiated B lymphocyte. In contrast, the levels of PKC-alpha mRNA remain high in plasma cell tumors, and a novel, 2.5-kb PKC-alpha mRNA gains prominence. PKC-eta mRNA is the major PKC isoform expressed in T lymphocytes, but it also is highly abundant in some myeloid lines. PKC-delta is expressed at high levels in all the lines we studied, whereas PKC-epsilon and -zeta are found in most cells but only at rather low levels. Analysis of myeloid clones derived from bipotential B lineage progenitor cell lines suggests that the B cell phenotype is associated with the expression of PKC-alpha. The close correlation of protein levels with mRNA levels indicates that PKC expression in hemopoietic cells is mainly regulated at the level of mRNA. The lineage- and differentiation stage-specific patterns of PKC-isozyme expression presented here suggest the involvement of specific PKC isozymes in differentiation as well as lineage determination of hemopoietic cells.

Animals↗

Induction of plasmacytomas secreting antigen-specific monoclonal antibodies with a retrovirus expressing v-abl and c-myc.

ABL-MYC, a recombinant murine retrovirus that expresses v-abl and c-myc, rapidly induces transplantable mono- or oligoclonal plasmacytomas in BALB/c mice. To determine if the targets for transformation of this retrovirus are antigen-committed B lymphocytes and to explore this system as an alternative technique for producing antigen-specific monoclonal antibodies, plasmacytomas were induced in mice that had been immunized with two different types of immunogens, hen egg white lysozyme and sheep red blood cells. The majority of these plasmacytomas secreted immunogen-specific antibodies. Plasmacytomas induced in unimmunized mice did not react with hen egg white lysozyme or sheep red blood cells. The specific antibodies were comparable in concentration, specificity, and affinity to monoclonal antibodies obtained with conventional hybridoma technology, but, in addition to IgGs and IgMs, they included specific IgA antibodies, which are rare among splenic-derived hybridomas. Our results demonstrate that a principal target for ABL-MYC is an antigen-committed B lymphocyte. In addition this procedure provides an alternative method for the production of monoclonal antibodies, without a requirement for hetero-caryon formation by cell fusion techniques.

Animals↗