Single-cell transcriptomic analyses reveal distinct immune cell contributions to epithelial barrier dysfunction in checkpoint inhibitor colitis

Immune checkpoint inhibitor (ICI) therapy has revolutionized oncology, but treatments are limited by immune-related adverse events, including checkpoint inhibitor colitis (irColitis). Little is understood about the pathogenic mechanisms driving irColitis, which does not readily occur in model organisms, such as mice. To define molecular drivers of irColitis, we used single-cell multi-omics to profile approximately 300,000 cells from the colon mucosa and blood of 13 patients with cancer who developed irColitis (nine on anti-PD-1 or anti-CTLA-4 monotherapy and four on dual ICI therapy; most patients had skin or lung cancer), eight controls on ICI therapy and eight healthy controls. Patients with irColitis showed expanded mucosal Tregs, ITGAEHi CD8 tissue-resident memory T cells expressing CXCL13 and Th17 gene programs and recirculating ITGB2Hi CD8 T cells. Cytotoxic GNLYHi CD4 T cells, recirculating ITGB2Hi CD8 T cells and endothelial cells expressing hypoxia gene programs were further expanded in colitis associated with anti-PD-1/CTLA-4 therapy compared to anti-PD-1 therapy. Luminal epithelial cells in patients with irColitis expressed PCSK9, PD-L1 and interferon-induced signatures associated with apoptosis, increased cell turnover and malabsorption. Together, these data suggest roles for circulating T cells and epithelial-immune crosstalk critical to PD-1/CTLA-4-dependent tolerance and barrier function and identify potential therapeutic targets for irColitis.

SARS-CoV-2 infection elucidates unique features of pregnancy-specific immunity

Pregnancy is a risk factor for increased severity of SARS-CoV-2 and other respiratory infections. The mechanisms underlying this risk have not been well-established, partly due to a limited understanding of how pregnancy shapes immune responses. To gain insight into the role of pregnancy in modulating immune responses at steady state and upon perturbation, we collected peripheral blood mononuclear cells (PBMC), plasma, and stool from 226 women, including 152 pregnant individuals (n = 96 with SARS-CoV-2 infection and n = 56 healthy controls) and 74 non-pregnant women (n = 55 with SARS-CoV-2 and n = 19 healthy controls). We found that SARS-CoV-2 infection was associated with altered T cell responses in pregnant compared to non-pregnant women. Differences included a lower percentage of memory T cells, a distinct clonal expansion of CD4-expressing CD8 + T cells, and the enhanced expression of T cell exhaustion markers, such as programmed cell death-1 (PD-1) and T cell immunoglobulin and mucin domain-3 (Tim-3), in pregnant women. We identified additional evidence of immune dysfunction in severely and critically ill pregnant women, including a lack of expected elevation in regulatory T cell (Treg) levels, diminished interferon responses, and profound suppression of monocyte function. Consistent with earlier data, we found maternal obesity was also associated with altered immune responses to SARS-CoV-2 infection, including enhanced production of inflammatory cytokines by T cells. Certain gut bacterial species were altered in pregnancy and upon SARS-CoV-2 infection in pregnant individuals compared to non-pregnant women. Shifts in cytokine and chemokine levels were also identified in the sera of pregnant individuals, most notably a robust increase of interleukin-27 (IL-27), a cytokine known to drive T cell exhaustion, in the pregnant uninfected control group compared to all non-pregnant groups. IL-27 levels were also significantly higher in uninfected pregnant controls compared to pregnant SARS-CoV-2-infected individuals. Using two different preclinical mouse models of inflammation-induced fetal demise and respiratory influenza viral infection, we found that enhanced IL-27 protects developing fetuses from maternal inflammation but renders adult female mice vulnerable to viral infection. These combined findings from human and murine studies reveal nuanced pregnancy-associated immune responses, suggesting mechanisms underlying the increased susceptibility of pregnant individuals to viral respiratory infections.

Immune Responses in Checkpoint Myocarditis Across Heart, Blood, and Tumor

Immune checkpoint inhibitors (ICIs) are widely used anti-cancer therapies that can cause morbid and potentially fatal immune-related adverse events (irAEs). ICI-related myocarditis (irMyocarditis) is uncommon but has the highest mortality of any irAE. The pathogenesis of irMyocarditis and its relationship to anti-tumor immunity remain poorly understood. We sought to define immune responses in heart, tumor, and blood during irMyocarditis and identify biomarkers of clinical severity by leveraging single-cell (sc)RNA-seq coupled with T cell receptor (TCR) sequencing, microscopy, and proteomics analysis of 28 irMyocarditis patients and 23 controls. Our analysis of 284,360 cells from heart and blood specimens identified cytotoxic T cells, inflammatory macrophages, conventional dendritic cells (cDCs), and fibroblasts enriched in irMyocarditis heart tissue. Additionally, potentially targetable, pro-inflammatory transcriptional programs were upregulated across multiple cell types. TCR clones enriched in heart and paired tumor tissue were largely non-overlapping, suggesting distinct T cell responses within these tissues. We also identify the presence of cardiac-expanded TCRs in a circulating, cycling CD8 T cell population as a novel peripheral biomarker of fatality. Collectively, these findings highlight critical biology driving irMyocarditis and putative biomarkers for therapeutic intervention.

Single-cell profiling of human heart and blood in immune checkpoint inhibitor-associated myocarditis

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Background: Myocarditis due to immune checkpoint inhibitors (ICIs) is uncommon; however, myocarditis due to ICIs leads to severe morbidity and even death in 20-40% of cases. The molecular underpinnings of ICI-associated myocarditis are poorly understood, and there is an unmet clinical need to identify therapeutic targets and biomarkers that can aid in disease management. Methods: Heart tissue was obtained through endomyocardial biopsy or autopsy of patients receiving ICIs and was profiled with paired single-cell RNA sequencing (scRNA-seq) and T cell receptor sequencing (TCR) using the 10x Genomics Chromium system. A control dataset was constructed using scRNAseq data of heart tissue from patients receiving ICIs but without myocarditis and a published dataset from healthy patients not receiving ICIs. Peripheral blood mononuclear cells (PBMCs) were collected at the time of myocarditis diagnosis in a larger cohort of patients and analyzed with ICI-treated controls. The CITE-Seq protocol was used to measure paired scRNA-seq, TCR, and surface proteomics in PBMCs, using serial timepoints where available. Results: Heart tissue from 13 patients with myocarditis, including three fatal cases, and seven controls yielded 77,712 single cells. Blood profiling from 27 patients with ICI myocarditis and ICI-treated controls across 54 samples yielded over 230,000 cells. ICI myocarditis tissue demonstrated an increased T cell infiltrate (OR 8.94, FDR = 0.0021). Expression of multiple inflammatory pathways, most notably interferon responses, was up-regulated across multiple immune and non-immune cell types in the setting of myocarditis, providing important pathophysiological insights. T cell clones were also found to be shared between blood and heart, enabling the identification of putative pathogenic T cell subsets. Conclusions: Increased intramyocardial T cells and the activation of interferon response gene networks were seen in the setting of ICI myocarditis. These preliminary findings highlight potential pathological pathways in ICI myocarditis that could serve as biomarkers or therapeutic targets.

Plasmacytoid dendritic cells: Welcome back to the DC fold

The presumed common origin of plasmacytoid and conventional dendritic cells has been the contentious subject of recent debate. In this issue of Immunity, Feng et al. employed an inducible cell barcoding system to track clonal relationships and uncovered a surprising close developmental relationship between cDC1s and pDCs.

c-Fos-related antigens in the central nervous system of an insect, Acheta domesticus

Fos-related antigens (Fra) were detected in the nuclei of neurones in young adult Acheta domesticus female crickets by immunohistochemical analysis, using an antibody that recognizes the amino-acid sequence 127-152 of c-Fos protein. Specificity of Fra immunoreactivity was confirmed by Western blot analysis of nuclear extracts from neural tissues. A major immunoreactive doublet with an apparent molecular mass of 52,000/54,000 Da was detected in nuclear extracts. Immunostaining of the 52,000/54,000 Da doublet showed variations in intensity during the first 5 days following the imaginal molt. Staining was more intense between day 2 and day 4 when ecdysteroid titers were high. Expression of Fra was low in allatectomized (i.e., deprived of juvenile hormone and ecdysteroids) and ovariectomized (i.e., deprived of ecdysteroids) females as compared to control females. These results show the involvement of hormone-regulated process in expression of Fra. The effect of nociceptive stimulation on Fra expression was tested. Twenty minutes after removal of the ovipositor, a supplementary band with an apparent molecular mass of 70,000 Da appeared in the nuclear extracts, then decreased and disappeared totally after 45 min. Several other Fos-related antigens with different temporal patterns of expression were also detected.

Identification of odorant receptors from the Alpine marmot (Marmota marmota)

Alpine Marmots (Marmota marmota) are a good model to study intraspecific chemical communication among mammals. This species has been subjected to several behavioural and biochemical studies regarding both their scent-marking behaviour by cheek-rubbing, and the chemical composition of their glandular secretions. However, no molecular study has been undertaken until today on proteins from the olfactory epithelium possibly implicated in chemical perception. In this study, we identified, to our knowledge for the first time, some olfatory receptors from this wild rodent. Starting with olfactory epithelium of an Alpine Marmot, and by mean of reverse transcriptase polymerase chain reaction technique (RT-PCR), we isolated fourteen partial sequences that exhibited a high degree of homology (45-92%) with olfactory receptors from other vertebrates. Conserved identities and structural features clearly defined these Alpine Marmot sequences as members of the seven transmembrane domain olfactory receptors. All sequences were observed as belonging to known olfactory receptor families and were classified into ten subfamilies of the tetrapods OR class. Finally, Northern blot analysis revealed specific expression of these sequences in the Alpine Marmot olfactory epithelium tissue.

Isolation of putative olfactory receptor sequences from pig nasal epithelium

Binding to olfactory receptors is the first step in odorant and pheromonal recognition and discrimination. These receptors constitute one of the most important, although poorly known, families of neuronal receptors. In this study we used degenerated oligonucleotides and a RT-PCR approach to selectively amplify olfactory receptors in the nasal epithelium of the domestic pig Sus scrofa. Several combinations of oligonucleotide were tested and allowed the isolation of eleven different partial sequences belonging to the seven transmembrane olfactory receptor family. These receptors formed a separate family within the seven transmembrane receptor superfamily in pigs. Using the criteria of Ben Arie et al. [Ben-Arie N., Lancet D., Taylor C., Khen M., Walker N., Ledbetter DH., Carrozzo R., Patel K., Sheer D., Lehrah H. and North M., Hum. Mol. Genet., 3 (1994) 229-235], the 11 receptors described here can be classified into three known families and seven subfamilies (one known and six new).

Casein kinase II activity in the brain of an insect, Acheta domesticus: characterization and hormonal regulation

This study documented casein kinase II (CK II) activity in Acheta domesticus brain using specific antibodies and its regulation by polyamines. In control animals a transient decrease in CK II activity at day 3 after imaginal moult was observed in the brain but not in the fat body. If deprived of ecdysone by ovariectomy a different pattern was observed, with CK II activity being significantly higher on days 3 and 4 after emergence. After ecdysone injection in ovariectomized females, CK II activity decreased to levels similar to those in controls. The implications of ecdysone regulation of brain CK II activity are discussed.

Induction of polarized apical expression and vectorial release of carcinoembryonic antigen (CEA) during the process of differentiation of HT29-D4 cells

HT29-D4 clonal cells can be induced to differentiate by a simple alteration of the culture medium, that is, by the replacement of glucose by galactose [Fantini, J., et al. (1986) J. Cell Sci., 83:235-249] as reported for the nonclonal HT29 cells [Pinto, M., (1982) Biol. Cell, 44:193-196]. An essential property of the HT29-D4 cell line is the fact that no cell loss occurs after the medium change, so that the differentiated cells can be considered as the true counterpart of the undifferentiated one. This model is particularly suitable to study morphological and biochemical events associated with the progressive establishment of the differentiation state. We report here that carcinoembryonic antigen (CEA), a 180 kDa glycoprotein originally described as a colon tumor associated antigen, is faintly expressed at the surface of undifferentiated HT29-D4 cells. These cells release a small amount of CEA (2.5 ng/10(6) cells/24 hr) in the culture medium. Fourty-eight hours after glucose substitution by galactose, both CEA cell surface expression and release are strongly enhanced as demonstrated by immunofluorescence and immunoprecipitation studies. Ten days after the medium change, the amount of CEA released reaches a maximum value of 130 ng/10(6) cells/24 hr, which remains stable for differentiated HT29-D4 cells cultured in glucose-free, galactose-containing medium (Gal-medium) for several months. HT29-D4 cells grown in Gal-medium in porous-bottom culture dishes generate leakproof epithelial monolayers. We have successfully performed an independent radioiodination of the apical and basolateral domains of these cells, followed by immunoprecipitation. We demonstrate that CEA is expressed exclusively at the apical surface of differentiated HT29-D4 cells, since the 180 kDa polypeptide was immunoprecipitated only when the radioiodination was performed at the apical side of the monolayer. Leakproof HT29-D4 monolayers cultured in permeable chambers were also used to demonstrate that CEA was exclusively released in the medium bathing the apical side of the cells. In conclusion, this study of cell surface CEA expression and CEA release during the process of differentiation of HT29-D4 cells demonstrated that 1) CEA cell surface expression and CEA release are correlated with cell differentiation; 2) CEA is expressed in the apical brush border membrane of differentiated HT29-D4 cells; and 3) CEA release is exclusively oriented toward the apical side of the polarized monolayer.

Restricted localization of functional vasoactive intestinal peptide (VIP) receptors in in vitro differentiated human colonic adenocarcinoma cells (HT29-D4)

HT29-D4, a clone of the human colonic adenocarcinoma cell line (HT29), possesses at its cell surface specific binding sites for the vasoactive intestinal peptide (VIP) (KD = 0.5 nM). Their molecular weight was previously estimated to 117 kDa and 64 kDa. This clone underwent functional and structural differentiation when grown in a glucose-free galactose-containing medium. The [125I]VIP binding capacity of cells grown in this medium gradually declined while the cell density increased and reached a value close to zero when cell monolayer was able to form hemicysts. At this time, cells presented numerous tight junctions and desmosomes and a well organized brush border. Binding capacity could be recovered when the post-confluent monolayers were previously disaggregated with EDTA. Neither the affinity for VIP nor the molecular weight of the [125I]VIP cross-linked polypeptides were modified in these cells compared to cells grown in glucose-containing medium. However, surface receptor number of differentiated cells was twice that of undifferentiated cells. Leakproof differentiated cell monolayers grown on permeable substratum produced cAMP in response to VIP only when the peptide was present in the lower chamber of the culture wells. Taking these data altogether, we conclude that the localization of functional VIP receptors is restricted to the basolateral domain in differentiated post-confluent HT29-D4 cells.

Growth in serum-free medium of human colonic adenocarcinoma cell lines on microcarriers: a two-step method allowing optimal cell spreading and growth

Human colonic adenocarcinoma cells have been successfully grown on polystyrene microcarriers by modifying the culture conditions used in monolayer culture. The method can be divided into two culture phases: a) a phase of spreading, wherein cells were seeded in presence of serum-supplemented medium; b) a phase of active growth wherein spread cells on the beads were allowed to grow in a serum-free medium. Under these conditions, optimal spreading and growth of HT 29 and HRT 18 cells on the microcarriers were obtained. A differential propagation was observed between HT 29-D4 and HT 29-D9 cells (both clonal populations derived from HT 29 cells) on the microcarriers that is tentatively related to the discrepancy observed in the spreading efficiency of these clonal cells on serum-coated culture flasks. An index of spreading efficiency (IS index) has been defined to quantify the efficiency of spreading of each cell line on microcarriers. These data gave the opportunity to develop serum-free, scale-up methods to culture cells like HT 29 which release potentially useful products.

Evidence for an ectophosvitin kinase activity that phosphorylates a 123 kDa endogenous substrate on a human colonic adenocarcinoma cell (HT 29)

When HT 29 cells grown as a monolayer were incubated in a synthetic medium in presence of 0.1 microM [gamma 32P]-ATP, the radioactivity was incorporated predominantly into three major endogenous polypeptides of 123 kDa, 50 kDa and 46 kDa. The radioactive proteins could be detected as soon as 30 s after the addition of the labelled ATP. When exogenous substrates such as casein or phosvitin were added in the synthetic medium, these proteins became phosphorylated. The phosvitin-kinase activity was released in the culture medium following an incubation of the cells with phosvitin. Depletion of the enzymatic activity from the cell surface as well as competition between phosvitin and endogenous substrates led specifically to the inhibition of the 123 kDa polypeptide phosphorylation. At low density, endogenous phosphorylation increased with the cell number, whereas on the contrary it decreased at high cell density. We concluded that the surface of HT 29 cells expressed several protein kinase activities. We have characterized one of them as an ectophosvitin kinase which phosphorylated specifically a 123 kDa polypeptide and whose expression or accessibility varied according to cell density.

Spontaneous and induced dome formation by two clonal cell populations derived from a human adenocarcinoma cell line, HT29

The replacement of glucose by galactose in the culture medium resulted in partial structural and functional enterocytic differentiation of HT29 cells. In order to characterize populations of homogeneously differentiated HT29 cells we have selected two clonal cell lines HT29-D4 and HT29-D9 with the following functional and structural characteristics when grown in a galactose-containing medium: the two clonal cell populations were permanently morphologically differentiated as shown by the presence of mature junctional complexes and a well-organized brush border (especially for HT29-D4 cells); HT29-D4 and HT29-D9 cells were able to form domes early in confluency, which indicated a functional state of differentiation; the process of differentiation was fully reversible when glucose was added to the culture medium. The induction of domes was investigated in these two cell populations and we demonstrated for the first time that proteolytic enzymes are potent inducers of dome formation. The architecture of domes either obtained spontaneously or induced by proteolytic enzymes was not maintained in the presence of ouabain (a specific inhibitor of the Na+/K+-ATPase). In conclusion, HT29-D4 and HT29-D9 cells can be maintained permanently in a differentiated state in a glucose-free medium and were able to form domes at confluency. The observation that proteolytic enzymes were able to induce dome formation can help in the comprehension of the mechanism involved in the establishment of the differentiated state.

Monensin and tunicamycin-induced inhibition of HT29 cell spreading and growth

HT29 cells originating from a human colon adenocarcinoma, spread very rapidly after seeding on their own extracellular matrix (ECM). Preincubation of cells with the inhibitor of protein glycosylation tunicamycin (TM) or with the ionophore monensin substantially suppressed cell spreading in serum-free medium without affecting cell adhesion to ECM. Addition of the drugs after cell attachment and spreading inhibited cell growth. TM-treated cells remained viable after 6 days of exposure to 2 micrograms ml-1 of TM and resumed their normal growth rate and shape after removing the drug from the medium. On the contrary, monensin inhibition of cell growth was not reversible: after 3 days, cells detached from the ECM and were unable to exclude Trypan Blue. At the ultrastructural level, a swollen Golgi apparatus with numerous vacuoles was observed after treatment for 2 h in either TM or monensin-preincubated cells. These results suggest that TM and monensin interfere with the insertion and, or, function of one or more cell surface glycoproteins, possibly interacting with cytoskeleton and involved in cell spreading and growth.

Characterization of the vasoactive intestinal peptide (VIP) binding sites: a biochemical and an immunological approach

The initial event of VIP action is its interaction with a specific receptor at the surface of a target cell. The understanding of the fine mechanism of action of VIP requires the characterization and of course the purification of the receptor. The understanding of the mechanism which regulates the number of receptor sites at the cell surface, if it occurs, is also a way to characterize the properties of VIP receptor. In this paper we report a number of data which represent several attempts to characterize VIP receptor in a human colonic adenocarcinoma cell (HT 29 cells). We have characterized a monoclonal antibody which partially inhibits 125I-VIP binding to HT 29 cells. We have specifically cross-linked, on intact HT 29 cells, a major polypeptide of Mr-64,000 with 125I-VIP using DTSP or DSS as cross-linking reagents. This polypeptide behaves like a high affinity binding site for VIP. We have demonstrated that VIP is rapidly internalized in HT 29 cells (in less than 10 minutes) and that simultaneously VIP receptors were no more detectable on the cell surface by cross-linking experiments. This suggests that VIP is internalized together with its receptor.

Histone phosphorylation in native chromatin induces local structural changes as probed by electric birefringence

In order to understand how the phosphorylation of histones affects the chromatin structure, we used electron microscopy, sedimentation velocity, circular dichroism and electric birefringence to monitor the salt-induced filament reversible solenoid transition of phosphorylated and native chromatin. Phosphorylation in vitro of chicken erythrocyte chromatin by cyclic-AMP-dependent protein kinase from porcine heart led to the modification of the histones H3 and H5 only, which were modified at a level of one phosphate and about three phosphate groups per molecule, respectively. In contrast to circular dichroism and sedimentation studies, which tend to suggest that phosphorylation of H3 and H5 does not affect chromatin structure, electron microscopy reveals that phosphorylation causes a relaxation of structure at low ionic strength. Electric birefringence and relaxation time measurements clearly prove that local structural changes are induced in chromatin: we observe a decrease of the steady-state birefringence with the appearance of a negative contribution in the signal and a marked increase of the flexibility of fibres. The component with the negative birefringence presents very short relaxation times, like those exhibited by small DNA fragments or individual nucleosomes. Two possibilities are then suggested. First, the conformational change is consistent with what would be expected from the presence of DNA segments loosely associated with the core histone H3. That the length of such segments could correspond to about one to two base-pairs per nucleosome strongly suggests that phosphorylation induces changes affecting some specific H3-DNA interactions only. This result could corroborate previous observations indicating that the N-terminal region of H3, where the site of phosphorylation is located, plays a decisive role in maintaining the superstructure of chromatin. Second, phosphorylation could introduce hinge points between each nucleosome. In this case, the negative birefringence results from partial orientation of the swinging nucleosomes. A possible mode of action of phosphorylation might be to weaken structural restraints imposed by histone H3, thus facilitating further condensation of chromatin.

Cyclic AMP binding proteins in the rat thyroid cytosol. Effects of suppression and stimulation of thyroid activity

Suppression of thyroid activity by treatment of rats with thyroxine in vivo significantly decreases the relative concentration of protein kinase regulatory subunits in the thyroid cytosol. Stimulation by thyroid-stimulating hormone (TSH) in rats previously treated by thyroxine for 5 days significantly increases the relative concentration of regulatory subunits. Two species of regulatory subunits of protein kinases were separated by ion exchange chromatography. The observed modifications after thyroxine and TSH treatment affect both species of regulatory subunits to the same extent, whereas chronic stimulation by propylthiouracil for 30 days preferentially increases the type II regulatory subunit.

Thyrotropin-induced increase in phosphoprotamine phosphatase activity in rat thyroid

Phosphoprotamine phosphatase activity in the rat thyroid was examined by studying the release of inorganic phosphate from [32P]-phosphorylated protamine. Rats were given a normal diet supplemented or not with thyroxine (T4) (3 mg/l in 0.05% bovine serum albumin solution) or propylthiouracil (1 g/l in 1% sucrose solution) in drinking water for various periods. TSH was injected ip, 100 mU per animal. A significant increase of phosphatase specific activity-units per mg protein (3-fold) as well as units per gland- was observed following goitrogen treatment, whereas a decrease (50%) was seen in response to T4. Both the soluble and particle activities were similarly affected. As total activity decreased after T4 treatment, it appeared that only the Mn2+-stimulating enzyme was concerned, the Mn2+-unstimulated part remaining unaltered. In vitro cyclic AMP or cyclic GMP at concentrations from 10 micro M to 200 micro M had no effect on these phosphatase activities. TSH injected in chronically T4-treated rats (32 days treatment) failed to produce any significant enhancement in phosphatase activity whatever the time of injection before sacrifice (from 2 to 6 h). On the contrary a single injection of TSH in animals subjected to short treatment with T4 (2 days) induced an elevation of the enzyme activity, restoring partially the initial level. These findings suggest that TSH controls protein dephosphorylation activities in the thyroid. Furthermore, they offer additional evidence that prolonged T4 administration leads to decreased responsiveness to TSH.

Cyclic AMP-binding proteins and protamine kinases in porcine thyroid cytosol

Partial purification of cyclic AMP-binding proteins from porcine thyroid cytosol was performed by gel filtration on Bio Gel 1.5 m followed by ion exchange chromatography on DEAE Sephadex A25. Three fractions presenting cyclic AMP-binding activities were resolved by gel filtration (I, II, III). Approximate molecular weights were respectively 280 000, 145 000 and 65 000. Fraction I was further resolved into two peaks (Ialpha and Ibeta) on DEAE-Sephadex A25. Fractions I, Ialpha, Ibeta comigrated with protein kinase activity whereas peaks II and III did not. These fractions differed with respect to the folling characteristics: rate and stability of cyclic AMP binding to isolated fractions were differently affected by pH (4.0 or 7.5). Electrophoretic mobility on polyacrylamide gels (5%) of fractions preincubated with cyclic [3H]AMP showed similar mobilities for Ialpha, Ibeta or II (Rf 0.37) whereas fraction III displayed a much greater mobility (RF 0.73); Scatchard plots were linear for fractions Ialpha, II and III with an apparent Kd in the same range (2 to 5 nM) whereas fraction Ibeta generated a biphasic plot with Kd 0.4 nM and 20 nM; cyclic [3H] AMP added to fraction I, Ialpha or Ibeta generated a cyclic [3H] AMP-binding protein complex of lower molecular weight as shown by Sephadex G 150 filtration; on the basis of the elution volume, this complex was not distinguished from fraction II. In the course of this work, we separated at the first step of purification (Bio Gel 1.5 m) a protein kinase not associated with cyclic AMP binding activity which exhibited marked specificity for protamine as compared to histone II A.

Liver protein kinase activity and triiodothyronine

Protein kinase activities were determined in liver from normal, thyroidectomized and triiodothyronine (T3)-treated rats. Changes related to thyroid hormone were observed in cytosol and nuclear protein kinase activities. When protamine was used as substrate for phosphorylation, thyroidectomy induced a decrease of protein kinase activity associated with nuclei but an increase of activity was found in the cytosol. Fifteen hours after injection of T3 the levels in nuclei and cytosol were restored to normal. When casein was used as substrate, hypothyroidism led to a lowering of protein kinase activity in both fractions and T3 treatment augmented the activity in both. These studies suggest that thyroid hormones modify hepatic protein kinase activity. Results differ depending upon the substrate used. The hormones also appear to alter the subcellular distribution of some protein kinase activities.

Factors influencing triiodothyronine binding properties of liver nuclear receptors

Triiodothyronine (T3) may bind directly to receptors present in liver cell nuclei, or may be transported into nuclei by receptor protein(s) present in the cytosol. To evaluate these possibilities, T3 binding was studied in vitro using liver cell nuclei isolated from rats exposed in vivo to very low (H), normal (N),or high levels of T3 (H + T3), and using nuclei incubated in vitro with added cytosol proteins. Ka for T3 was 0.075 +/- 0.05 x 10(10) M-1 in N, 0.1 + 0.04 in H, and 0.094 + 0.04 in H + T3, and pg T3 bound/100 mug DNA were 47 +/- 17, 31 +/- 14, and 29 +/- 8 in the three groups. The data indicate no difference in binding capacity between the groups related to prior in vivo exposure to T3, and that T3 may bind directly to empty nuclear receptor sites. Rat liver cytosol proteins added to the in vitro incubation medium always depressed T3 uptake by nuclei. Bovine serum albumin had a similar effect. Large amounts of rat serum proteins depressed uptake, but low levels augmented T3 binding through an unknown mechanism. It is probable that free T3 in serum is in equilibrium with free T3 in the cytosol and nucleus, and binds directly to nuclear receptor proteins without mediation by a cytosol receptor protein.

Phosphorylation of purified thyroid plasma membranes incubated with [32-P]ATP

Plasma membranes have been prepared from porcine thyroid glands using sucrose gradients. The fractions having a density in sucrose of 1.18 g/ml mainly contained plasma membranes and were moderately contaminated with other subcellular components as shown by marker enzyme data. Purified plasma membranes incubated in the presence of [32-P]gamma ATP incorporated 32-P. Kinetics of incorporation of 32-P into endogenous substrates studied in various buffers and with increasing ATP concentration suggest a phosphodephosphorylating system related to cAMP-dependent protein kinase and phosphoprotein phosphatase activities. The two enzymatic activities associated with plasma membranes have been demonstrated using exogenous substrates. cAMP increases and fluoride ions decrease the extent of membrane phosphorylation. The specific activity of protein kinase was 10-12 times higher than in the initial homogenate and was only slightly enhanced in the presence of 0.5% Nonidet as compared to microsomal fraction. cAMP binding to membrane proteins was 3 times higher than to the other particulate fractions. TSH present in the incubating medium or added after 5 min of 32-P labelling induced a rapid stimulation of endogenous phosphorylation followed by a rapid decrease. Phosphorylated membrane substrates were analyzed: high voltage paper electrophoresis after partial hydrolysis indicated that [32-P]phosphate is incorporated into serine and threonine residues as o-phosphate derivatives. SDS-polyacrylamide gel electrophoresis showed several 32--labelled fractions. When enhanced by cAMP, no specific phosphorylation of protein components was observed.