Clonal extinction of myelomonocytic leukemic cells by serum from mice injected with endotoxin

Culture of WEHI-3B myelomonocytic leukemic cells in semi-solid agar medium containing post-endotoxin serum led to the development of maturing granulocytes and macrophages in most leukemic colonies. Colony size was consistently increased but the colony content of colony-forming cells (stem-cell self-replication) was markedly reduced. Serial recloning of WEHI-3B colony cells in the continuous presence of post-endotoxin serum led to clonal extinction of the leukemic cells in five of seven experiments. These effects of post-endotoxin serum on WEHI-3B cells were not seen in clonal cultures of 10 other tumor lines. Serum with the capacity to induce differentiation in WEHI-3B cells could be induced by the injection of as little as 0.1 microgram endotoxin and by purified bacterial cell-wall preparations. Serum activity reached peak levels 3 - 6 h after endotoxin injection and returned to preinjection levels within 48 h.     

Modulation of homeobox B6 and B9 genes expression in human leukemia cell lines during myelomonocytic differentiation

Homeobox genes (HOX) may have a regulatory function in the differentiation process of hematopoiesis. We examined the change of HOX B6 and HOX B9 mRNA expressions during the in vitro differentiation of four myeloid leukemia cell lines because HOX B6 may be involved closely in myeloid differentiation. HL-60, NB4, NKM-1 and NOMO-1 were established from acute leukemia of M2, M3, M2 and M5 subtype of the French-American-British classification, respectively. All-trans retinoic acid (ATRA), TPA, and G-CSF were used as differentiation inducers. Each cell line was cultured with each inducer and total RNA was isolated on day 1, 2, 3, or 5. HOX B mRNA was detected by Northern blotting and RT-PCR methods. HOX B6 and HOX B9 mRNAs were constitutively expressed in NB4, NKM-1 and NOMO-1, but were expressed at very low levels in HL-60. HOX B6 and HOX B9 mRNAs were also expressed in fresh acute myelocytic leukemia blasts. HOX B6 mRNA expression in HL-60, NB4, and NKM-1 cultured with ATRA increased on day 3 and decreased on day 5. HOX B6 mRNA expression in NB4 and NKM-1 cultured with TPA decreased on day 3. HOX B9 mRNA expression displayed changes similar to those of HOX B6 mRNA in NB4 and NKM-1. These results indicate that myeloid leukemia cell lines express HOX B6 and HOX B9, and that their respective mRNA expressions in NB4 and HL-60 increase at a mid stage of myeloid differentiation by ATRA induction and then decrease during a late stage. HOX B6 mRNA expression decreased in monocytoid differentiation by TPA induction in NB4, HL-60 and NKM-1. HOX B6 antisense-oligonucleotide inhibited the proliferation of NB4 and NKM-1. These results suggest that HOX B gene expression is related to simultaneous activation of cellular proliferation and differentiation in leukemic cells.     

Circumferential forearm fasciocutaneous free flap reconstruction of forequarter amputation/chest wall resection using simultaneous extra-anatomic revascularization (SEAR)

In recent years, many cytokines have been defined and some of them used clinically. In hematological malignancies, cytokines, including granulocyte colony-stimulating factor (G-CSF), have been widely used for leukopenia after chemotherapy. However, in acute myelogenous leukemia (AML), some leukemic cells may be induced to proliferate by these cytokines and they must be used with care. In this study, we have investigated cell reactivity and proliferation with G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CMF), macrophage colony-stimulating factor (M-CSF), stem cell factor (SCF) and thrombopoietin (TPO) in cases of AML. We have also investigated the reactivity of some myeloid leukemia cell lines to TPO. G-CSF, GM-CSF, M-CSF, SCF and TPO caused proliferation of leukemic cells in 25%, 58.3%, 8.3%, 21.1% and 0% of cases, respectively. Because of this result, the use of G-CSF in AML should be regarded as potentially hazardous. TPO did not cause proliferation of leukemic cells in any case of AML, or in cell lines except MO7E, which is a megakaryocytic cell line. This result suggests that TPO might cause proliferation of some megakaryocytic leukemia cells. We cannot conclude that TPO does not cause proliferation of other AML cells, as the number of cases was small and it has been reported elsewhere that leukemia cells may proliferate when exposed to TPO in 50% of AML cases. Reactivity of AM L cells to TPO is an important factor when deciding the indications of TPO in AML and myelodysplastic syndrome.     

A genetic system to detect mitotic recombination between repeated chromosomal sequences in Drosophila Schneider line 2 cells

In order to study mitotic homologous recombination in somatic Drosophila melanogaster cells in vitro and to learn more on the question how recombination is influenced by mutagens, a genetic system was developed where spontaneous and drug-induced recombination could be monitored. Two recombination reporter substrates were stably introduced in multiple copies into the genome of established D. melanogaster Schneider line 2 cells: one plasmid (pSB310) contained the 5' and 3' deleted neomycin phosphoribosyltransferase alleles neoL and neoR as direct repeats; the other (pSB485) contained similar deletions (lacZL and lacZR) of the beta-galactosidase gene (lacZ). Restoration of a functional neo gene upon mitotic recombination between homologous sequences allowed direct selection for the event, whereas recombination in single cells harbouring the integrated lacZ-based reporter plasmid was detected by histochemical staining or flow cytometric analysis (FACS). The neo-based construct in the clonal transgenic cell line 44CD4 showed a spontaneous recombination frequency of 2.9 x 10(-4), whereas the 485AD1 cell line harbouring the lacZ-based construct exhibited a frequency of 2.8 x 10(-4). The alkylating agents EMS and MMS and the clastogen mitomycin C were able to induce recombination in the 485AD1 cell line in a dose-dependent manner. The results obtained from these studies suggest that the transgenic cell lines are potentially useful tools for identifying agents which stimulate direct repeat recombination in somatic Drosophila cells.     

Proteins and cells on PEG immobilized silicon surfaces

Functional adhesion of blood and marrow leukemic cells from 14 acute myeloid leukemia patients presenting with hyperleukocytosis was evaluated by performing cytoadhesion assays on purified (extracellular matrix proteins) and non-purified supports (MRC5 fibroblastic cell line). Results, in 30-min chromium release assay, show a mean +/- S.D. adhesion to fibronectin, collagen, and laminin respectively of 30 +/- 17%, 20 +/- 13%, 25 +/- 17% for blood leukemic cells and 18 +/- 11%, 11 +/- 10%, 11 +/- 8% for marrow leukemic cells. These differences between blood and marrow cells were statistically significant (respectively P = 0.005, P = 0.01 and P = 0.002), while no difference was noted regarding adhesion to non-purified supports. The higher adhesion of blood blast cells to purified supports was observed regardless of CD34 expression. No significant difference was observed in the expression of cell surface VLA-molecules (CD29, CD49b, CD49d, CD49e, CD49f) between blood and marrow blast cells. The addition of GM-CSF or G-CSF induced increased adhesion of marrow blasts and decreased adhesion of blood blasts leading to a loss of the difference between blood and marrow cells. In a 60-min chromium release assay, marrow blasts adhered even more than blood leukemic cells to fibronectin. In contrast, marrow blasts from 'aleukemic' acute myeloid leukemia patients did not show any modification regarding their adhesion to extracellular matrix proteins when co-cultured with growth factors.     

Variable morphological differentiation of a raphé-derived neuronal cell line following transplantation into the adult rat CNS

A clonal, neuronally-differentiating cell line, RN33B, was previously developed by retroviral infection of neural tissue derived from embryonic Sprague-Dawley raphé nuclei with a retrovirus encoding the temperature-sensitive allele of SV40 large T-antigen. In the present study, RN33B cells were transplanted into two target areas of the raphé nuclei, the spinal cord and hippocampal formation, of adult allogeneic hosts. Prior to transplantation, RN33B cells were infected in vitro with a retroviral vector carrying the Escherichia coli lacZ reporter gene and were visualized in vivo using a beta-galactosidase immunohistochemical technique. RN33B cells were seen throughout the spinal cord and hippocampal formation of the adult hosts at 15 days post-transplantation. T-antigen-immunoreactive nuclei were detected where RN33B cells were observed, but in much greater numbers than beta-galactosidase-immunoreactive cells. Bipolar RN33B cells were found in the spinal cord grey matter. RN33B cells with multipolar morphologies were visualized in the hippocampal and subicular pyramidal cell layers, and also in the dentate gyrus granule cell and polymorph layers, while bipolar RN33B cells were seen in the remainder of the hippocampal formation. The results suggest that immortalized neural cell lines of CNS origin can differentiate in the adult CNS with their ultimate morphology being determined by local tissue signals. We speculate that endogenous neutrophins may significantly influence RN33B cell differentiation in vivo.     

Analysis of a multi-mutant herpes simplex virus type 1 for gene transfer into sympathetic preganglionic neurons and a comparison to adenovirus vectors

A non-replicating triple-mutant herpes simplex virus (14H delta 3vhsZ) expressing the bacterial marker enzyme beta-galactosidase, was assessed for neurotropism and cytopathic effects as a vector for gene transfer into differentiated phaeochromocytoma 12 cells in vitro and into spinal sympathetic neurons in vivo. In the in vivo study, the 14H delta 3vhsZ was injected into the adrenal gland of hamsters. For comparison, an evaluation of two adenovirus vectors, AdCA17lacZ and AdCA36lacZ, was performed. Infection of the differentiated phaeochromocytoma 12 cells by 14H delta 3vhsZ resulted in intense beta-galactosidase staining in 80-90% of the cells without changes in cell morphology, detected by light microscopy, after a period of four days. No cytoskeletal disruption was detected by immunocytochemistry for the neurofilament protein and no apoptosis was demonstrated by the Hoescht stain for nuclear chromatin in virus-infected cells in comparison to mock-infected control cells. Twoto three days after adrenal inoculation with 14H delta 3vhsZ, beta-galactosidase was detected in 240 preganglionic neurons per hamster (n = 8), a number equal to about 25% of the population of targeted neurons. The beta-galactosidase reaction product extended throughout the normal kite-shaped neuronal somata and extensive dendritic arbour. The number decreased to 120 by five days (n = 3) and to two by eight days (n = 4). This decrease was presumably due to loss of expression of the marker gene and not to cell death because, at eight days, the number of sympathetic pregnanglionic neurons in the nucleus intermediolateralis, pars principalis, that were immunoreactive for the neurotransmitter enzyme choline acetyltransferase, and demonstrated nicotinamide adenine dinucleotide phosphate-diaphorase activity, were the same on the infected left side of the cord as on the uninfected right side. Inflammatory cells surrounded some of the infected neurons at five days but by eight days the infiltrate was reduced. Infection of differentiated phaeochromocytoma 12 cells by AdCA17lacZ and AdCA36lacZ also resulted in marker gene expression in a large proportion of the cells (80-90%) in the absence of cytopathic effects. In contrast, four days after adrenal injection of AdCA17lacZ or AdCA36lacZ (n = 5 for each) only an average of three preganglionic neurons per hamster expressed beta-galactosidase activity, despite clear adrenal infection. AdCA17lacZ and AdCA36lacZ both produced light patches of staining confined to the neuronal soma. These neurons had normal morphology but sometimes were surrounded by an inflammatory infiltrate. In conclusion, the non-replicating herpes simplex virus, 14H delta 3vhsZ, had minimal cytotoxic effects in neurons, in vitro or in vivo, and was efficiently transported from the adrenal gland to infect many sympathoadrenal pregnanglionic neurons. In contrast, very few neurons demonstrated beta-galactosidase activity after injection into the adrenal gland of AdCA17lacZ and AdCA36lacZ. Therefore, 14H delta 3vhsZ is a more suitable vector than either of the adenovirus vectors tested for eliciting short-term changes in preganglionic neuron gene expression.     

c-KIT expression enhances the leukemogenic potential of 32D cells

The growth of human leukemic cells in culture and in vivo is dependent upon the presence of hematopoietic growth factors. Most populations of human leukemic acute myeloblastic leukemia (AML) cells express c-Kit on their surface and respond to Kit ligand (KL) in culture. To determine if this interaction was of potential significance in vivo we used a mouse model system. 32D cells, a murine IL-3-dependent myeloid cell line, were rendered KL responsive by transfection of the murine c-Kit. After injection of 32D or 32D-Kit cells into syngeneic hosts, animals bearing 32D-Kit cells, but not 32D cells, became moribund and were killed. These animals had circulating leukemic blast cells, infiltration of bone marrow, spleen, brain, liver, lung, and kidney. Cells recovered from some of the animals continued to be dependent upon IL-3 or KL for growth while in other cases the cells were factor independent. This model illustrates that the constitutive expression of c-Kit enhances the leukemic potential of 32D cells. The model will be useful for studying the progression of leukemia in vivo and testing whether interruption of the interaction of Kit and KL can affect the growth of leukemic cells.     

Impact of in vivo administration of interleukin 3 on proliferation, differentiation, and chemosensitivity of acute myeloid leukemia

Early clinical trials of growth factor augmentation of induction chemotherapy for acute myeloid leukemia have yielded variable results. To test the hypothesis that this heterogeneity is a consequence of the pleiotropic effects of growth factors on leukemic cell biology, we measured the effects of in vivo interleukin 3 (IL-3) administration on leukemic cell proliferation and drug sensitivity. Thirty-four patients with acute myeloid leukemia with high-risk features or advanced myelodysplasia received IL-3 as a continuous infusion beginning 3 days prior to chemotherapy and continuing for the duration of intensive induction therapy. Bone marrow cells were studied prior to and after 3 days of IL-3 administration to assess changes in overall and leukemic progenitor cell [leukemia colony-forming unit (CFU-L)] proliferation, and progenitor cell sensitivity to 1-betad-arabinofuranosylcytosine. The median fold increase in overall leukemic cell proliferation in response to IL-3, assessed as expression of the nuclear antigen Ki67 in 28 patients, was 1.2. The median fold increase in percentage of cells in S phase (assessed in 29 patients) was 1.3. Despite the increase in overall cell proliferation in 70% of cases, CFU-L number increased in only 4 of 20 patients successfully studied (median day 4:day 1 ratio of CFU-L number, 0.6). While this suggests possible terminal differentiation of leukemic progenitor cells, expression of CD34, HLA-DR, c-kit, CD15, and CD14 were not consistently affected by the cytokine. 1-betad-Arabinofuranosylcytosine sensitivity of CFU-L increased significantly in 30% of cases, decreased in 30%, and was unchanged in 40%. Changes in overall cell proliferation (Ki67 expression) and CFU-L were independent predictors of change in 1-beta-d-arabinofuranosylcytosine sensitivity; increase in percentage of cells in S phase in response to IL-3 was correlated with attainment of complete remission. While these findings support the concept of cell cycle recruitment, IL-3 has marked pleiotropic effects on proliferation, differentiation, and survival of leukemic progenitors which make the clinical impact of in vivo cytokine administration for individual patients difficult to predict.     

Ligation of cell surface CD38 protein with agonistic monoclonal antibody induces a cell growth signal in myeloid leukemia cells

CD38 is expressed during early stages of differentiation in normal and leukemic myeloid cells. Recently, CD38 has been shown to participate in intracellular signal transduction pathways following its ligation with CD38-specific mAbs. In this study we report that ligation of CD38 by one such agonistic mAb (IB4) induced proliferation of cultured leukemic cells in vitro. In HL-60, KG-1A, NB4, and OCI-AML-3 myeloid leukemia cell lines, IB4 mAb induced an increase in the proliferating cell fraction as determined by cell number, clonogenic assay, and flow cytometric analysis. The presence of Ab caused a dose-dependent increase in the number of CFU and an increase in cell divisions. HL-60-Dox cells (a HL-60-doxorubicin-resistant cell line), which have no detectable CD38 expression, failed to respond to IB4 mAb. The effect of CD38 ligation on cell growth was also evaluated in freshly isolated leukemic cells from patients with acute myelogenous leukemia (AML). A significant increase in the proliferating cell fraction (S+G2M) was observed in 50% of the patients incubated with IB4 mAb. In five of the six AML patients, anti-CD38 mAb stimulated the proliferation of AML colony-forming cells. These results suggest that ligation of CD38 can induce the proliferation of leukemic cells and may play a role in the propagation of leukemic cell clones in certain cohorts of AML patients.     

Unimpaired macrophage differentiation and activation in mice lacking the zinc finger transplantation factor NGFI-A (EGR1)

The zinc finger protein NGFI-A (also called EGR1, Krox24, or zif268) is a candidate regulator of myeloid cell differentiation. Evidence supporting this hypothesis is twofold. First, NGFI-A antisense oligonucleotides prevent macrophage differentiation in HL-60 and U937 myeloid leukemia cell lines and in normal bone marrow cells. Second, enforced expression of NGFI-A blocks granulocytic differentiation and promotes macrophage differentiation in HL-60 cells and in the hematopoietic progenitor cell line 32D. We sought to determine the effect of NGFI-A deficiency on macrophage differentiation and function in vivo by examining native bone marrow cells from mice homozygous for a disrupted allele of NGFI-A derived from gene-targeted ES cells. Macrophages were observed in peripheral blood and several tissues, indicating that NGFI-A was not required for the formation of a variety of macrophage compartments. No differences in myeloid cell differentiation were observed between wild-type and NGFI-A-/- bone marrow cells cultured in the presence of macrophage, granulocyte-macrophage, or granulocyte colony-stimulating factor (M-CSF, GM-CSF, or G-CSF). Activation of NGFI-A-/- macrophages was comparable to that of wild-type macrophages as determined by nitric oxide production and increased cell surface expression of class II major histocompatibility complex molecules. Moreover, NGFI-A-/- mice showed no increased mortality or bacteria] burden when challenged with Listeria monocytogenes. Together, these results indicate that NGFI-A is not required for macrophage differentiation or activation.     

Injection of apomorphine into the medial prefrontal cortex of the rat increases haloperidol-induced catalepsy

We compared telomere length in donor leukemic cells and corresponding established cell lines from three patients with chronic myeloid leukemia (CML) and three with acute lymphoblastic leukemia (ALL) to study the relation between the immortalization capacity of hematologic neoplasms and telomere length. Six of the seven established leukemia cell lines (four CML and two ALL) carried additional chromosome changes and had shorter telomere repeats than those of the donor patients' leukemic cells; the remaining ALL line showed no significant difference in telomere length between fresh leukemic cells and the corresponding cell line. Thus, most established leukemic cells lose effective telomerase activity during the process of establishment, and reduction in telomere length of established leukemic cells appeared to be associated with the presence of additional chromosome changes.     

Atherosclerosis in transplant heart

The effects of both daily G-CSF administration and subsequent peripheral blood progenitor cell collection (PBPCC) by apheresis on 20 healthy adult donors were studied. All received daily G-CSF (filgrastim) 10 micrograms/kg for 5-7 days by subcutaneous injection. G-CSF administration was well tolerated, except for moderate bone pain and headache. Peak values of CD34+ cells were observed on days 5 (n = 12) or 6 (n = 8). In all donors a significant increase in CD3+, CD4+, CD8+, CD19+, and NK cells was observed on day 5 in relation to the baseline values. CD4/CD8 lymphocyte ratio was unmodified by G-CSF. None of the donors required a central venous line for PBPCC. Immediately after PBPCC, a platelet count below 100 x 10(9)/1 was observed in nine of 18 cases, although in all donors platelet counts were over 100 x 10(9)/1 7 days later. A lymphocytopenia on day 7 following PBPCC was observed, although there was a tendency to achieve baseline values 30-90 days after the procedure. Mean numbers ( +/- SD) of collected cells x 10(6)/kg after a median of two (1-4) apheresis sessions and a median of 20 1 (10-40) processed were: CD34+ 5.5 ( +/- 2.3), CD3+ 326 ( +/- 105), CD4+ 207 ( +/- 64), CD8+ 164 ( +/- 60), CD19+ 88 ( +/- 32), and NK cells 32 ( +/- 14). We conclude that G-CSF administration to healthy donors is a well-tolerated procedure which is associated with (a) obtaining a high number of hematopoietic progenitor cells, and (b) a significant increase in T, B, and NK cells in donors' blood. In addition, PBPCC by apheresis results in a moderate, rapidly reversible, and clinically irrelevant thrombocytopenia and a moderate lymphocytopenia, which tends to resolve within 3 months following the procedure.     

The pharmacology of impulsive behaviour in rats III: the effects of amphetamine, haloperidol, imipramine, chlordiazepoxide and ethanol on a paced fixed consecutive number schedule

Granulocyte-colony stimulating factor (G-CSF) was originally found to induce proliferation and differentiation of normal granulocyte progenitors. Recent studies demonstrated that G-CSF induces growth of some malignant cells, including lymphoid cells. G-CSF is now widely and successfully used to treat neutropenia induced by intensive chemotherapy, and the responsive growth of malignant cells becomes a major clinical issue. Adult T-cell leukemia (ATL) is a malignant lymphoid disease of T cells, etiologically associated with human T cell lymphotropic virus type I (HTLV-I). We demonstrated that primary ATL cells in about 80% of patients expressed cell surface G-CSF receptor (G-CSFR). Our recent data also show that ATL cells from a third of the patients show responsive growth to G-CSF ex vivo. Several patients whose ATL cells proliferated in response to G-CSF showed a significant increase of the ATL cell count after administration of G-CSF in vivo. These observations suggest caution for it's routine clinical use in ATL. The molecular mechanism of G-CSF responsive growth of ATL cells is obscure, however the population of G-CSFR expressing cells is larger in responsive cases than in nonresponsive cases. Expression of G-CSFR on ATL cells may relate to the expression of Tax protein encoded by HTLV-I. Precise studies on G-CSFR signaling in ATL cells are necessary for the safe use of G-CSF routinely for ATL patients.     

Effect of dexamethasone and corticosterone on activity levels of ATPase, phosphomonoesterases and phosphodiesterase in liver, muscle and testis of post-hatched White Leghorn chicks

We have investigated the feasibility of using high-titer murine leukemia virus-based retroviral vectors to deliver exogenous genes to naive and chronically inflamed knee joints of rabbits in vivo. Intraarticular injection of retrovirus encoding beta-galactosidase (beta-gal or lacZ) was found to transduce synoviocytes in both naive and inflamed joints, but a significantly higher number of lacZ+ cells were found in inflamed knees. Using a retrovirus encoding a secretable marker, human growth hormone (hGH), quantitative comparison of ex vivo and in vivo gene delivery methods demonstrated that transgene expression following in vivo gene transfer was at least equivalent to that of the ex vivo method in inflamed knees. In addition, hGH transgene expression was maintained for at least 4 weeks. These experiments suggest that high-titer retroviral vector could be used for efficient in vivo gene transfer to inflamed joints in patients with rheumatoid arthritis (RA).     

Protein kinase C is not necessary for transforming growth factor beta-induced growth-arrest in leukemia cell lines

Growth and differentiation of blood cell precursors are regulated by cytokines and hormones by mechanisms which are incompletely understood. Protein kinase C (PKC) isozymes are widely regarded as being important in signal transduction pathways. We have shown that one isozyme, PKC beta, is uniquely important in mediating phorbol ester-induced growth-arrest in the HL-60 myeloid cell line. 1,25-dihydroxyvitamin D3 induces differentiation and growth-arrest in many cells. It upregulates the expression of PKC beta, potentiating the action of phorbol ester. We tested the hypotheses that cytokines, which arrest the growth of hematopoietic cells, do so by activating PKC beta, and that differentiation and growth-arrest induced by 1,25-dihydroxyvitamin D3 is caused by upregulation of PKC beta isozyme gene expression. The influence on growth of combinations of five cytokines (TNF alpha, TGF beta 1, gamma-IFN, IL-1, and G-CSF) and 1,25-dihydroxyvitamin D3 on ten human leukemia cell lines (THP-1, HL-60 S, HL-60 PET, U937, K562, Jurkat, MOLT-4, RPM1 8402, KG-1, and KG-1a) was determined. Four cell lines (THP-1, HL-60 S and PET, and U937) exhibited total growth-arrest when incubated with 1,25-dihydroxyvitamin D3 followed by TGF beta 1. The expression by each cell line of mRNA encoding PKC alpha, beta, and delta, both before and after 24 or 48 h of incubation with 1,25-dihydroxyvitamin D3, was determined. Cell lines sensitive to TGF beta 1 each expressed PKC delta endogenously, or expression was up-regulated with 1,25-dihydroxyvitamin D3. U937 cells underexpressed PKC alpha, and HL-60 PET cells underexpressed PKC beta. These data suggested that PKC delta could be responsible for mediating growth-arrest by TGF beta 1. To test this hypothesis directly, we incubated the cells with two bisindolylmaleimide PKC inhibitors during the addition of 1,25-dihydroxyvitamin D3 and TGF beta 1. Surprisingly, the PKC inhibitors did not block the growth-arrest induced by 1,25-dihydroxyvitamin D3 and TGF beta 1. This experiment strongly suggests that neither growth-arrest induced by TGF beta 1 nor the potentiation of this growth-arrest by 1,25-dihydroxyvitamin D3 is mediated by a PKC isozyme which is inhibitable by the bisindolymaleimides.