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Biomedical subjects

H Green

Publications and source records attributed to H Green.

At least 145 records · Page 8Linked to original sources
PubMed1982

Growth hormone and the adipose conversion of 3T3 cells.

Cultured preadipose 3T3 cells are induced or enabled to undergo adipose conversion in the presence of an extract of pituitary gland. Adipogenic activity is found in standard growth hormone preparations derived from different species. Further purification of rat growth hormone by several methods does not remove its adipogenic activity. Human growth hormone synthesized in Escherichia coli is also effective. Adipogenic activity is not associated with other pituitary polypeptides. Since growth hormone acts on preadipose cells in the absence of any other cell type, a mechanism exists for the direct participation of the pituitary gland in the regulation of this form of mesenchymal differentiation.

Adipose Tissue↗
PubMed1982

Regulation by vitamin A of envelope cross-linking in cultured keratinocytes derived from different human epithelia.

When keratinocytes derived from different squamous epithelia are cultured in the absence of vitamin A, they form cross-linked envelopes during the last stage of terminal differentiation. Addition of the vitamin inhibits envelope formation, but the degree of inhibition is not the same for different keratinocyte subtypes. In the presence of low concentrations of retinyl acetate, conjunctival keratinocytes form virtually no cross-linked envelopes; esophageal and vaginal keratinocytes are less sensitive to the vitamin, and epidermal keratinocytes are the least sensitive. The suppression of cross-linked envelope formation is not associated with a proportional decrease in the concentration of involucrin, a precursor of the envelope, but occurs at the level of cross-linking itself, a process dependent on an increase in the intracellular concentration of calcium ions. Keratinocytes in which spontaneous envelope cross-linking has been prevented by retinyl acetate promptly form cross-linked envelopes if Ca2+ is introduced into the cytoplasm.

Calcium↗
PubMed1981

Suppression of the adipose conversion of 3T3 cells by acidified serum.

The adipose conversion of cultured 3T3-F442A cells in strongly inhibited if the fetal bovine serum of the culture medium is briefly acidified before it is used. The inhibitory factor is a polypeptide with an apparent molecular weight of 24,000, and is inactivated by pronase or trypsin. Cells grown to confluence in the presence of this factor do not become spherical or accumulate triglyceride; they also do not increase the activity of their triglyceride-synthesizing enzymes. The factor suppresses adipose conversion even in the presence of untreated serum. Once adipose conversion has begun in the absence of the inhibitory factor, subsequent addition of the factor does not arrest the conversion.

Adipose Tissue↗
PubMed1981

Regulation of terminal differentiation of cultured human keratinocytes by vitamin A.

Vitamin A is known to exert an important influence on epithelial differentiation. The fetal calf serum supplement of cell-culture medium contains enough of the vitamin to affect the differentiation of cultured keratinocytes derived from epidermis and from other stratified squamous epithelia. The cellular and molecular properties of the cultures are altered when the medium is supplemented with serum from which the vitamin A has been removed by solvent extraction (delipidized serum). Cell motility is reduced, the adhesiveness of cells increases and pattern formation is prevented. In both epidermal and conjunctival keratinocytes, removal of vitamin A leads to the synthesis of a 67 kd keratin characteristic of terminally differentiating epidermis and to much reduced synthesis of the 52 kd and 40 kd keratins typical of conjunctiva. These changes, both cellular and molecular, are reversed by the addition of retinyl acetate to the medium containing delipidized serum. Cell motility and pattern formation are restored, and detachment of the most mature cells from the surface of the stratified epithelium is promoted. Synthesis of the 67 kd keratin is prevented and the synthesis of the 40 and 52 kd keratins is stimulated. The nature of the keratins synthesized is regulated by the concentration of vitamin A, and each cell type adjusts its synthesis differently at a given vitamin concentration.

Cell Aggregation↗
PubMed1981

Cyclic AMP-mediated control of lipogenic enzyme synthesis during adipose differentiation of 3T3 cells.

During the adipose differentiation of 3T3-F442A cells, there is an increase in the synthesis of numerous proteins, including the lipogenic enzymes glycerophosphate dehydrogenase, fatty acid synthetase and malic enzyme. Agents that increase cAMP content (Dibutyryl cAMP, theophylline, and isoproterenol) are known to induce lipolysis in fat cells; but the same agents are shown here to reduce the synthesis of the lipogenic enzymes during adipose differentiation. The extent of reduction depends on the agent used and differs for the three enzymes; fatty acid synthetase is most sensitive and its synthesis can be suppressed completely. In contrast to their effects on lipogenic enzyme synthesis, these agents do not affect morphological changes or the synthesis of several other proteins, of which some increase and others (such as actin) decrease during the differentiation. The effects of the agents on the synthesis of lipogenic enzymes are not dependent on lipolysis, since they take place to the same degree in cells not permitted to accumulate triglyceride. Translation in vitro of mRNA isolated from cells treated with the agents promoting cAMP accumulation indicates that the levels of functional mRNA for lipogenic enzymes are reduced. We conclude that, in addition to its activation of lipolysis, cAMP reduces specifically mRNA accumulation for lipogenic enzymes. These results also demonstrate the independent control of morphological change and enzyme synthesis during adipose differentiation.

Adipose Tissue↗
PubMed1981

Two distinct classes of keratin genes and their evolutionary significance.

Bacterial plasmids containing cDNA sequences specific for keratins were constructed from mRNA of cultured human epidermal cells. Two separate classes of cloned cDNAs were identified by positive hybrid selection: one class removed from total human epidermal mRNA a fraction that was translated into 56 and 58 kilodalton (kd) keratins, and the other class selected mRNAs that translated into a mixture of 50 kd and 46 kd keratins. When probes specific for these two keratin classes were hybridized with human DNA digested with a restriction endonuclease that does not cleave within the probe, two distinct patterns of about ten fragments each were observed. Most of the hybridizing genomic fragments corresponded to complete cDNA sequences, and it is estimated that each of the two classes is encoded by about 10 genes. When the probes were hybridized with DNA from different species, all vertebrates were found to contain discrete sequences homologous to both human keratin probes. Within each vertebrate species, the two probes always hybridized with approximately equal intensities to nonoverlapping sets of genomic sequences, suggesting a coordinate evolution between the two subfamilies of keratin genes. This finding has important functional implications for keratin filament assembly.

Animals↗
PubMed1981

Adipogenic and anti-adipogenic factors in the pituitary and other organs.

Adipose conversion of cultured 3T3 cells is known to depend on an adipogenic factor present in serum. In the presence of this factor, extracts of different organs were found to inhibit the adipose conversion. The most active extracts were derived from brain, uterus, and pituitary, but other organs also possessed appreciable activity. Fibroblast growth factor partially purified from both brain and pituitary was much more active in suppressing adipose conversion than were crude extracts of the corresponding organs. Purified platelet-derived growth factor was also an effective inhibitor. Of all the tissue extracts tested, only pituitary possessed, in addition to the inhibitory activity, an adipogenic factor similar to that demonstrated previously in serum. This was revealed at concentrations of extract too low for the inhibitory factor to be effective. Under these conditions the pituitary extract had a specific adipogenic activity orders of magnitude higher than that of serum. We suggest that the adipogenic factor of serum may originate in the pituitary.

Adipose Tissue↗
PubMed1981

Involucrin synthesis and tissue assembly by keratinocytes in natural and cultured human epithelia.

Different stratified squamous epithelia, whether they bear a stratum corneum or not, are shown by immunofluorescence to possess the precursor protein of the cross-linked envelope that is characteristic of epidermal s. corneum. This protein, involucrin, is not present in the deepest epithelial cells but appears in the course of their outward migration. The boundary at which involucrin first appears can sometimes by correlated with a visible boundary between zones of large and small cells. Cultured keratinocytes, derived from all stratified squamous epithelia (epidermal, corneal, conjuctival, esophageal, lingual, and vaginal), form colonies that grow together to form a stratified epithelium. The cells of the basal layer are nearly always free of detectable involucrin, but, in contrast to the natural epithelium, this protein usually makes its appearance in the cells immediately above the basal layer. When a cultured epithelium derived from epidermal keratinocytes is detached and applied as a graft to animals, the cells flatten and the distinctness of the basal layer is at first reduced; but with time the organization of the epithelium becomes more characteristic of epidermis. Cell size and shape become more orderly along the cell migration pathway, and involucrin first appears at some distance from the basal layer, instead of in immediately suprabasal cells, as in the cultured epithelium. The progeny of dissociated and cultured keratinocytes are therefore able, when grafted, to reassemble an epidermis in which the timing of specific gene expression is restored to that of the original tissue.

Cells, Cultured↗
PubMed1981

Involucrin synthesis is correlated with cell size in human epidermal cultures.

Late in terminal differentiation, human epidermal keratinocytes form an insoluble protein envelope on the cytoplasmic side of the plasma membrane. Involucrin, a soluble protein precursor of the envelope, is synthesized at an earlier stage of differentiation, both in the natural epithelium and in cultured keratinocytes. Because keratinocytes are known to enlarge during differentiation, we looked for a correlation between involucrin synthesis and cell size, using antiserum raised against the purified protein. We found that virtually no cultured epidermal keratinocytes with a diameter less than or equal to 14 micrometer contained involucrin, but most cells greater than 17 micrometer did. Using density gradient centrifugation, we were able to isolate a population of small cells containing almost no involucrin, as judged by immunodiffusion, PAGE, and immunoprecipitation. Large cells possessed translatable mRNA for involucrin, whereas small cells did not. We conclude that when cultured keratinocytes reach a certain size (approximately 14 micrometer in diameter) the specific mRNA for involucrin begins to accumulate and synthesis of the protein begins.

Cell Separation↗
PubMed1980

Changes in keratin gene expression during terminal differentiation of the keratinocyte.

Cells of the inner layers of the epidermis contain small keratins (46-58K), whereas the cells of the outer layers contain large keratins (63-67K) in addition to small ones. The changes in keratin composition that take place within each cell during the course of its terminal differentiation result largely from changes in synthesis. Cultured epidermal cells resemble cells of the inner layers of the epidermis in synthesizing only small keratins. The cultured cells possess translatable mRNA only for small keratins, whereas mRNA extracted from whole epidermis can be translated into both large and small keratins. As no synthesis takes place in the outermost layer of the epidermis (stratum corneum), the keratins of this layer must be synthesized earlier, but in some cases they then become smaller: this presumably occurs by post-translational processing of the molecules during the final stages of differentiation. Stratified squamous epithelia of internal organs do not form a typical stratum corneum and do not make the large keratins characteristic of epidermis. Their keratins are also different from those of cultured keratinocytes, implying that they have embarked on an alternate route of terminal keratin synthesis.

Animals↗
PubMed1980

Formation of epidermis by serially cultivated human epidermal cells transplanted as an epithelium to athymic mice.

Human epidermal cells were grown serially in surface culture by inoculation of suspensions of disaggregated cells. Single cells grew into colonies and the colonies fused to make a confluent epithelium. The epithelium was detached as a unit and transplanted onto a graft bed prepared in athymic mice. Such grafts formed epidermis complete with stratum corneum. Although they became considerably reduced in area, the grafts remained healthy for as long as 108 days after grafting. The human origin of the grafts was demonstrated with a species-specific antiserum to a precursor protein of the cross-linked envelope.

Animals↗