Demonstration that a chemically synthesized BPV1 oncoprotein and its C-terminal domain function to induce cellular DNA synthesis

Bovine papillomavirus type 1 contains the smallest known oncogene (ORF E5), encoding a hydrophobic 44 amino acid protein. To study the biochemical functions of the E5 oncoprotein, we have chemically synthesized it and several deletion mutant peptides. We demonstrate induction of cellular DNA synthesis in growth-arrested cells by microinjection of E5 oncoprotein. This activity can be broken down into two functionally distinguishable domains. Remarkably, the first domain, which alone is sufficient to induce cellular DNA synthesis, contains only the C-terminal 13 amino acids. This is the smallest known protein fragment that can autonomously activate cellular DNA synthesis. The second domain is the hydrophobic middle region, which by itself fails to induce cellular DNA synthesis but confers a 1000-fold increase in specific activity. The N-terminal one-third of the molecule is dispensable for induction of DNA synthesis.     

Induction of macrophage-mediated cytolysis of neoplastic cells by mycoplasmas

Unexpected cytolysis was encountered when nonactivated murine peritoneal macrophages were cultured with [³H]TdR-prelabeled syngeneic or allogeneic tumor cells at a 10:1 ratio. The level of specific cytolysis reached 70% within 48 hr of cocultivation. Similar killing was observed whether the macrophages were derived from untreated, thioglycollate-treated, or germ-free mice. Cytolytic activity was also demonstrated when bone marrow-derived or peritoneal macrophages from 9- and 5-day in vitro cultures, respectively, were employed rather than freshly harvested peritoneal macrophages. Thus, the macrophage-mediated killing was neither the result of in vivo preactivation nor a consequence of the presence of lymphocytes in the assay. Moreover, macrophages derived from different strains caused similar effects. Our study revealed that the neoplastic target cell cultures susceptible to cytolysis by nonactivated macrophages were contaminated with mycoplasma. A mycoplasma was isolated from the supernatant of a culture of the A9HT fibrosarcoma line, identified as Mycoplasma orale, and cultivated. Addition of viable mycoplasma from that isolate to mixed cultures of thioglycollate-elicited macrophages and [³H]TdR-prelabeled mycoplasma-free target cells resulted in specific cytolysis of transformed A9 cells, but not of normal mouse fibroblasts. The level of macrophage-dependent cytolysis correlated with the number of viable mycoplasma cells added and was higher than that attained by activation with LPS at optimal concentration. Similar specific cytolysis was observed with heat-killed mycoplasmas. Our results demonstrate that mycoplasmas may cause selective macrophage-mediated cytolysis of neoplastic but not of normal target cells, perhaps via activation of the macrophages. It is suggested that undetected infection of experimental systems by mycoplasmas may account for some reports on lysis of neoplastic cells by nonactivated macrophages.     

The actions of retinoids on cellular growth correlate with their actions on gap junctional communication

Retinoic acid (a possible morphogen), its biological precursor retinol, and certain synthetic derivatives of retinol profoundly change junctional intercellular communication and growth (saturation density) in 10T 1/2 and 3T3 cells and in their transformed counterparts. The changes correlate: growth decreases as the steady-state junctional permeability rises, and growth increases as that permeability falls. Retinoic acid and retinol exert quite different steady-state actions on communication at noncytotoxic concentrations in the normal cells: retinoic acid inhibits communication at 10(-10)-10(-9) M and enhances at 10(-9)-10(-7) M, whereas retinol only enhances (10(-8)-10(-6) M). In v-mos-transformed cells the enhancement is altogether lacking. But regardless of the retinoid or cell type, all growth responses show essentially the same dependence on junctional permeability. This is the expected behavior if the cell-to-cell channels of gap junctions disseminate growth-regulating signals through cell populations.     

Some Electrical Properties of a Nuclear Membrane Examined with a Microelectrode

Electrical potential and resistance were measured with microelectrodes in in situ and isolated nuclei of gland cells of Drosophila flavorepleta. The nucleus-cytoplasm boundary was found to be rather impermeable to ion diffusion. It presents a resistance of the order of 1 Ω cm² and sustains a "resting" potential, the nucleoplasm being about 15 mv negative with respect to the cytoplasm. Both the resistance and potential appear to be associated with the nuclear membrane: the potential declines to zero and the resistance to a fraction of its original value, when the membrane is perforated experimentally.     

Incorporation of the gene for a cell-cell channel protein into transformed cells leads to normalization of growth

Summary Incorporation of the gene for connexin 43, a cell-cell channel protein of gap junction, into the genome of communication-deficient transformed mouse 10T1/2 cells restored junctional communication and inhibited growth. Growth was slowed, saturation density reduced and focus formation suppressed, and these effects were contingent on overexpression of the exogenous gene and the consequent enhancement of communication. In coculture with normal cells the growth of the connexin overexpressors was completely arrested, as these cells established strong communication with the normal ones. Thus, in culture by themselves or in coculture, the connexin overexpressor cells grew like normal cells. These results demonstrate that the cell-cell channel is instrumental in growth control; they are the expected behavior if the channel transmits cytoplasmic growth-regulatory signals.     

Growth inhibition of transformed cells correlates with their junctional communication with normal cells

The growth of various chemically and virally transformed cell types in culture is inhibited when they are in contact with normal cell types. We show that this growth inhibition is contingent on the presence of junctional communication between the normal and transformed cells (heterologous communication), as probed with a 443 dalton microinjected fluorescent tracer. In cell combinations where heterologous communication is weak or absent there is no detectable growth inhibition; the inhibition appears when communication is induced by cyclic AMP-dependent phosphorylation, and only then. In cell combinations where heterologous communication is spontaneously strong, the growth inhibition is present, but it is abolished when the communication is blocked by retinol or retinoic acid. The cell-to-cell membrane channels of gap junctions are the likely conduits of the signals for this growth control.     

Identifying Emotions on the Basis of Neural Activation

We attempt to determine the discriminability and organization of neural activation corresponding to the experience of specific emotions. Method actors were asked to self-induce nine emotional states (anger, disgust, envy, fear, happiness, lust, pride, sadness, and shame) while in an fMRI scanner. Using a Gaussian Naïve Bayes pooled variance classifier, we demonstrate the ability to identify specific emotions experienced by an individual at well over chance accuracy on the basis of: 1) neural activation of the same individual in other trials, 2) neural activation of other individuals who experienced similar trials, and 3) neural activation of the same individual to a qualitatively different type of emotion induction. Factor analysis identified valence, arousal, sociality, and lust as dimensions underlying the activation patterns. These results suggest a structure for neural representations of emotion and inform theories of emotional processing.     

Downregulation of cell-to-cell communication by the viralsrc gene is blocked by TMB-8 and recovery of communication is blocked by vanadate

Summary The viralsrc gene downregulates junctional communication, closing cell-to-cell membrane channels presumably by way of the phosphoinositide signal route. We show that TMB-8 [8-N, N-(diethylamino) octyl-3,4,5-trimethoxybenzoate] counteracts this downregulation in cells transformed by temperature-sensitive mutant Rous sarcoma virus: TMB-8 (36–72 m) raises junctional permeability when applied during activity ofsrc protein kinase, i.e., at steady permissive temperature; and TMB-8 inhibits the fall of junctional permeability, when the activity ofsrc protein kinase gets turned on. TMB-8 also (reversibly) inhibits the growth of the cells at permissive temperature and reverses the morphological changes associated with transformation. The morphological reversal lags several hours behind the junctional-permeability reversal. Communication recovers within a few minutes when the activity of thesrc protein kinase is turned off (in absence of TMB-8). Sodium orthovanadate (20 m) prevents this recovery, but it has no major effect on junctional permeability on its own. We discuss possible modes of action of these agents on critical stages of the signal route, related to intracellular Ca²⁺ and protein kinase C.