Transcriptional regulation of a tumor promoter and mitogen-inducible gene in human lymphocytes

Down-regulation of protein kinase C is due to an increased rate of degradation

The phorbol-ester-induced loss of protein kinase C that has been documented in many cell types appears to be a critical event in the generation of a cellular refractory state. We have investigated here the synthesis and degradation of the protein kinase C polypeptide in order to determine why its steady-state amounts are depleted in response to phorbol esters. These results indicate that depletion is due to an increased rate of degradation, with no change either in mRNA amounts or in rates of polypeptide synthesis.

Induction of metallothionein and other mRNA species by carcinogens and tumor promoters in primary human skin fibroblasts

We used nucleic acid hybridization and cDNA cloning techniques to isolate human sequences that respond to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). These clones were used as probes to examine changes of gene expression that occurred after the proliferation of exponentially growing primary human fibroblasts was arrested. Transcript levels detected by these probes were increased coordinately by treatment of the cells with UV light, mitomycin C, TPA, or the UV light-induced extracellular protein synthesis-inducing factor EPIF (M. Schorpp, U. Mallick, H. J. Rahmsdorf, and P. Herrlich, Cell 37:861-868, 1984). Proteins coded for by these transcripts were characterized by hybrid-promoted translation and by cDNA sequencing. One of the cDNA clones was homologous to the metallothionein IIa gene, and one set of related clones selected RNA for the secreted TPA-inducible protein XHF1 (U. Mallick, H. J. Rahmsdorf, N. Yamamoto, H. Ponta, R.-D. Wegner, and P. Herrlich, Proc. Natl. Acad. Sci. USA 79:7886-7890, 1982).

Cell cycle dependent genes inducible by different mitogens in cells from different species

A number of genes and cDNA sequences (including at least four oncogenes) are known to be expressed in a cell cycle-dependent manner, i.e. the levels of specific mRNAs vary with the phases of the cell cycle. In order to explore the significance of some of these sequences in the mitogenic response, we have investigated the expression of 8 cell cycle-dependent sequences (plus two control sequences, not expressed in a cell cycle-dependent manner) under a variety of conditions. These conditions included cells of different types, from different species, stimulated to proliferate by different mitogens. The genes (or sequences) studied included five cDNA clones whose sequences are preferentially expressed in early G1, i.e. two cDNA clones inducible by platelet-derived growth factor (JE-3 and KC-1), and three cDNA clones inducible by serum (2A9, 2F1, 4F1); and three oncogenes (c-myc, c-rasHa and p53) whose expression is known to be cycle-dependent. All of the tested genes, except 2A9, c-rasHa and the control genes, are expressed in a cell cycle-dependent manner in human peripheral blood mononuclear cells stimulated by phytohemagglutinin and in serum-stimulated mouse and Syrian hamster fibroblasts. The inducibility of these genes by different mitogens in cells of different types and from different species strongly suggests that these genes play a role in cell cycle progression. This conclusion is further supported by the known structural and functional similarities between cell-cycle dependent genes, oncogenes and genes coding for cell-cycle related molecules.

Expression of cell cycle-dependent genes in young and senescent WI-38 fibroblasts

We studied the expression of 11 cell cycle-dependent genes in senescent WI-38 fibroblasts and compared the results to those obtained in WI-38 cells from early passages (young cells). Every gene we examined is expressed in the senescent cells at levels similar to those in the young cells, including two genes maximally expressed at the G1/S phase boundary--genes for thymidine kinase and histone H3. The results clearly show that senescent, noncycling WI-38 cells are not similar to quiescent cells. Rather, such senescent WI-38 cells may be blocked just prior to the onset of DNA synthesis.

Induction of metallothionein and other mRNA species by carcinogens and tumor promoters in primary human skin fibroblasts

We used nucleic acid hybridization and cDNA cloning techniques to isolate human sequences that respond to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). These clones were used as probes to examine changes of gene expression that occurred after the proliferation of exponentially growing primary human fibroblasts was arrested. Transcript levels detected by these probes were increased coordinately by treatment of the cells with UV light, mitomycin C, TPA, or the UV light-induced extracellular protein synthesis-inducing factor EPIF (M. Schorpp, U. Mallick, H. J. Rahmsdorf, and P. Herrlich, Cell 37:861-868, 1984). Proteins coded for by these transcripts were characterized by hybrid-promoted translation and by cDNA sequencing. One of the cDNA clones was homologous to the metallothionein IIa gene, and one set of related clones selected RNA for the secreted TPA-inducible protein XHF1 (U. Mallick, H. J. Rahmsdorf, N. Yamamoto, H. Ponta, R.-D. Wegner, and P. Herrlich, Proc. Natl. Acad. Sci. USA 79:7886-7890, 1982).

Human T-cell growth factor (interleukin 2) and gamma-interferon genes: expression in human T-lymphotropic virus type III- and type I-infected cells

Acquired immune deficiency syndrome (AIDS) is characterized by severe depletion of OKT4+ T lymphocytes and leukemia is associated with abnormal proliferation of maturation-arrested lymphocytes. Human T-lymphotropic virus type III (HTLV-III) or lymphoadenopathy virus (LAV) and type I (HTLV-I) are etiologically linked to AIDS and adult T-cell leukemia/lymphoma, respectively. T-cell growth factor (TCGF, also known as interleukin 2) is required for the growth of activated T-cells, which play an important role in immune regulation. gamma-Interferon (IFN-gamma) is also implicated in immune modulation. It was possible that T-cell depletion in acquired immune deficiency syndrome could be due to an impairment of TCGF synthesis and that adult T-cell leukemia could be due to unregulated production of TCGF. The results reported here show that the transcription of the TCGF gene was not impaired in cultured HTLV-III-infected cells. Paradoxically, the TCGF gene in HTLV-I-infected cells was transcriptionally inactive. The reverse was the case for the gamma-interferon gene--it was actively transcribed in HTLV-I-infected cells but not in the HTLV-III-infected and virus-producing H9 and H4 cell line. No evidence was obtained suggesting abnormal regulation of the TCGF or of the IFN-gamma gene consequent to HTLV-III infection. It thus appears that in both HTLV-III and HTLV-I infection, growth control and immune regulatory mechanisms may bypass a modulatory role of TCGF or of IFN-gamma.

Expression of cell-cycle-dependent genes in phytohemagglutinin-stimulated human lymphocytes

We have investigated the expression of certain cell-cycle-dependent genes in human peripheral blood mononuclear cells (PBMC) stimulated by phytohemagglutinin (PHA). The genes studied had been previously identified as cell-cycle dependent in other cell types from different species and were induced by different mitogens. One of these genes (2F1) and the gene for the interleukin 2 receptor were induced by PHA even in cultures partially depleted of accessory cells where the lymphocytes grew in size but failed to enter S phase. The other genes (c-myc, 4F1, JE-3, and KC-1) were induced only in complete cultures of PBMC stimulated by PHA. These results confirm the dissociation between growth in size and cell DNA replication that can occur during cell-cycle progression. Moreover, the time course of appearance of detectable levels of RNA for these genes suggests that they may be used as markers of cell-cycle progression in the transition of lymphocytes from G0 to S phase.