Intercellular communication and tissue growth. 3. Thyroid cancer.

Intercellular communication was examined in normal and cancerous isolated thyroids with an intracellular electrical technique. The cells of normal thyroid (rat, mouse, hamster, man) communicate, within any given follicle, through permeable junctions. The cells of a wide variety of thyroid cancers (rat, hamster) do not communicate to any detectable degree and have resting membrane potentials lower than those of normal cells.

Intercellular communication and tissue growth. I. Cancerous growth.

Intercellular communication was examined with intracellular electrical techniques in primary and transplanted rat liver cancers. Normal liver cells communicate rather freely with each other through permeable junctional membranes. Cancer liver cells show no communication at all; their surface membrane is a strong barrier to diffusion all around the cell. Cancer cells induce alterations in membrane permeability in normal liver cells; communication among the latter is markedly reduced when cancer cells grow near them.

Structure of coupled and uncoupled cell junctions.

Cells of Chironomus salivary glands and Malpighian tubules have junctions of the "septate" kind. This is the only kind of junction discerned which is large enough to effect the existing degree of intercellular communication. The electron microscopic observations of the "septate" junction conform to a honeycomb structure, with 80-A-thick electron-opaque walls and 90-A-wide transparent cores, connecting the cellular surface membranes. A projection pattern of light and dark bands (the "septa") with a 150-A periodicity results when the electron beam is directed normal to any set of honeycomb walls. Treatment of the salivary gland cells with media, which interrupt cellular communication (without noticeable alteration of cellular adhesion) by reducing junctional membrane permeability or perijunctional insulation, produces no alterations in the junctional structure discernible in electron micrographs of glutaraldehyde-fixed cell material.

Intercellular communication and tissue growth. II. Tissue regeneration.

Intercellular communication was examined in regenerating rat liver and urodele skin, two tissues of fast but normal growth. In both, cellular communication is in general as good as in their respective normal intact state. This stands in striking contrast to the lack of cellular communication in tissues with cancerous growth. Upon wounding of the urodele skin, the normally permeable junctional membranes of cells near the wound border seal themselves off, thereby insulating the interiors of the communicated cell systems from the exterior. When the cells of two opposing borders make mechanical contact in the course of wound closure, communication between them ensues within 30 min. Within this period all cell movement also ceases ("contact inhibition"). The possible implications of these findings in the control of tissue growth are discussed.

Differential regulation of communication by retinoic acid in homologous and heterologous junctions between normal and transformed cells.

The permeability of junctions between cells of the same type (homologous junctions) is greatly increased by retinoic acid (10(-9)-10(-8) M), a probable morphogen, and this responsiveness is shared by a variety of normal and transformed cell types (Mehta, P.P., J.S. Bertram, and W.R. Loewenstein. 1989. J. Cell Biol. 108:1053-1065). Here we report that the heterologous junctions between the normal and transformed cells respond in the opposite direction; their permeability is reduced by retinoic acid (greater than or equal to 10(-9) M) and its benzoic acid derivative tetrahydrotetramethylnaphthalenylpropenylbenzoic acid (greater than or equal to 10(-11) M). The opposite responses of the two classes of junction are shown to be concurrent; in cocultures of normal 10T1/2 cells and their methylcholanthrene-transformed counterparts, the permeability of the heterologous junctions, which is lower than that of the homologous junctions to start with, falls (within 20 h of retinoid application), at the same time that the permeability of the homologous junctions rises in both cell types. Such a counter-regulation requires a minimum of three degrees of cellular differentiation. A model is proposed in which the differentiations reside in a trio of junctional channel protein. The principle of the model may have wide applications in the regulation of intercellular communication at tissue boundaries, including embryonic ones.

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.

Neural differentiation, NCAM-mediated adhesion, and gap junctional communication in neuroectoderm. A study in vitro.

We studied the development of NCAM and gap junctional communication, and their mutual relationship in chick neuroectoderm in vitro. Expression of NCAM, as detected by monoclonal and polyclonal antibodies, and development of junctional communication, as detected by extensive cell-to-cell transfer of 400-500-D fluorescent tracers, occurred in cultures from stage-2 embryos onward. Both expressions presumably required primary induction. The differentiating cells formed discrete fields of expression on the second to third day in culture, with the NCAM fields coinciding with the junctional communication fields delineated by the tracers. Other neural differentiations developed in the following order: tetanus toxin receptors, neurofilament protein, and neurite outgrowth. Chronic treatment with antibody Fab fragments against NCAM interfered with the development of communication, suggesting that NCAM-mediated adhesion promotes formation of cell-to-cell channels. Temperature-sensitive mutant Rous sarcoma virus blocked (reversibly) communication and the subsequent development of neurofilament protein and neurites, but expression of NCAM continued.

Calcium ion distribution in cytoplasm visualised by aequorin: diffusion in cytosol restricted by energized sequestering.

The distribution of Ca2+ in the cytoplasm following a local rise in Ca2+ concentration is visualized by means of aequorin luminescence and a television system with an image intensifier. Diffusion of Ca2+ through the cytosol is so constrained that a rise in cytoplasmic Ca2+ concentration produced by local Ca2+ entry through cell membrane or by local Ca2+ injection is confined to the immediate vicinity of these sites. The diffusion constraints are lifted by treatment with cyanide or ruthenium red. Thus, energized calcium sequestering, probably by mitochondria, is the dominant factor in the constraints. In cell regions where the sequestering machinery is sufficiently dense, different Ca2+ message functions inside a cell may be effectively segregated, permitting private-line intracellular communication.

Development of a receptor on a foreign nerve fiber in a Pacinian corpuscle.

When the sensory fiber of a Pacinian corpuscle (in cat mesentery) is transected (at the inferior mesenteric nerve) transduction fails within 30 hours: the nerve ending produces no generator potentials in response to mechanical stimulation. Electrically elicited nerve impulse conduction continues for at least another 18 hours. A transducer mechanism develops on a regenerating nerve fiber when this fiber enters the denervated corpuscle. Such transducer development takes place on myelinated fibers from the inferior mesenteric nerve, which normally supplies corpuscles, as well as on myelinated hypogastric nerve fibers, which normally do not go to corpuscles, including fibers larger than the original corpuscle afferents.

Permeability of the cell-to-cell membrane channels in mammalian cell juncton.

The channels in the junctions of various mammalian cell types--primary cultures and lines--were probed with a series of linear fluorescent amino acid and peptide molecules of different size and charge. Permeability is limited by probe size and electronegativity, these two factors apparently being related reciprocally. In respect to both factors, mammalian junctional channels are more restrictive than insect channels; hence the mammalian channels are narrower, more polar, or both. The channels of the various mammalian cell types differed slightly from each other; in some types the serum of the culture medium affected the channel permeability.