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At least 613 records · Page 34Linked to original sources
PubMed1994

Phosphorylation of caldesmon by smooth-muscle casein kinase II.

A caldesmon kinase activity was partially purified from an extract of chicken gizzard smooth muscle by sequential chromatography on columns of DEAE-Sephacel, MonoQ and Superose 12. This kinase was identified as casein kinase II by Western blotting using peptide-directed antibodies raised against the alpha, alpha' and beta subunits of human casein kinase II; the smooth muscle enzyme consisted of similar subunits of M(r) 43,000 (alpha), 39,000 (alpha'), and 27,000 (beta). Phosphorylation of caldesmon and casein by smooth muscle casein kinase II was optimal at approximately 0.1 M NaCl, did not require second messengers, and was inhibited by heparin. The kinase utilized either GTP or ATP as a substrate. Caldesmon was phosphorylated to approximately 1 mol Pi mol-1 caldesmon by smooth muscle casein kinase II with a Km for caldesmon of 4.9 microM. Two-dimensional thin-layer electrophoresis indicated phosphate incorporation into both serine and threonine. All the incorporated phosphate was recovered in the N-terminal peptide (residues 1-152) generated by cleavage at cysteine 153 with 2-nitro-5-thiocyanobenzoic acid. Purification of tryptic phosphopeptides and N-terminal sequencing revealed two principal sites of phosphorylation: serine 73 and threonine 83. The following four synthetic peptides corresponding to this domain of caldesmon were examined as substrates of casein kinase II: A = RRREVNAQNSVAEEE; B = AQNSVAEEE; C = RSTDDEAA; D = SVAEEETKRSTDDE. Interestingly, only peptides C and D were phosphorylated and both only at threonine. Phosphorylation of intact caldesmon did not affect the pattern of chymotryptic digestion suggesting that it does not induce a significant conformational change in the protein substrate. Phosphorylation also had no effect on the binding of caldesmon to actin or on the caldesmon-mediated inhibition of actomyosin MgATPase activity. However, phosphorylation completely abolished the interaction of caldesmon with immobilized smooth muscle myosin. These results are consistent with the localization of the myosin-binding domain near the N-terminus of caldesmon and of the actin-binding domain near the opposite end of the elongated molecule. Casein kinase II may therefore play a role in regulating caldesmon-myosin interaction and the ability of caldesmon to cross-link actin and myosin filaments in smooth muscle.

Adenosine Triphosphate↗
PubMed1995

Molecular phylogeny based on the kappa-casein and cytochrome b sequences in the mammalian suborder Ruminantia.

Nucleotide sequences for the kappa-casein precursor proteins have been determined from the genomic DNAs or hair roots of the Ruminantia. The coding regions, exons 2, 3, and 4, were amplified separately via the three kinds of PCRs and then directly sequenced. The primers were designed from the sequence of bovine kappa-casein gene; they were applicable for the amplification of the kappa-casein genes from the 13 species in the Ruminantia except exon 2 of the lesser mouse deer. These results permitted an easy phylogenetic analysis based on the sequences of an autosomal gene. A phylogenetic tree was constructed from the mature kappa-casein sequences and compared with the tree of the cytochrome b genes which were sequenced from the same individuals. The Cervidae (sika deer, Cervus nippon) were separated from the branch of the Bovidae on the tree of kappa-casein genes with a relatively high confidence level of the bootstrap analysis, but included in the branch of the Bovidae on the tree of cytochrome b genes. The kappa-casein tree indicated a monophyly of the subfamily Caprinae, although the internal branches were uncertain in the Caprinae. The tree based on the nucleotide sequences of cytochrome b genes clearly showed the relationships of the closely related species in the genus Capricornis consisting of serow (C. smatorensis), Japanese serow (C. crispus), and Formosan serow (C. swinhoei). These results would be explained by the difference of resolving power between the kappa-casein and the cytochrome b sequences.

Animals↗
PubMed1988

An improved purification procedure and properties of casein kinase II from brain.

A simple and short purification procedure applicable to casein kinase II has been developed, for fully characterizing the enzyme from calf cerebral cortex cytosol. The procedure consists of four chromatographic steps: DEAE-cellulose, phosphocellulose, phosvitin-Sepharose and ATP-agarose which yields 87% pure casein kinase II. The purified enzyme shows three major bands with apparent molecular masses of 42, 38, and 27 kDa by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and is self-autophosphorylated on its 27 kDa polypeptide. The enzyme shows all the characteristics described for casein kinase II from other sources: it is independent of cyclic nucleotides, calcium/phospholipids, and double-stranded poly(I).poly(C); it can utilize both ATP and GTP as phosphoryl donors and can phosphorylate both casein and phosvitin but not histone. The kinetic studies establish that the Km for ATP is 12.5 microM and 25.1 microM when using phosvitin and casein respectively as phosphoryl acceptors. The Km for phosvitin is 0.91 mg/ml and for casein 1.43 mg/ml, while the Vmax is 315 nmol/min/per mg protein and 479 nmol/min/per mg protein for phosvitin and casein respectively. The activity of the kinase is highly stimulated by KCl or NaCl, and almost completely inhibited by heparin concentrations of 1 microgram/ml (92%). This inhibition is reduced to only 33% in the presence of optimal KCl concentrations (150 mM). Spermine stimulates enzyme activity, whilst hemin produces a slight inhibition.

Animals↗
PubMed1983

Regression of casein and cholesterol-induced hypercholesterolaemia in rabbits.

Hypercholesterolaemia was induced in rabbits by feeding semipurified diets containing soy protein plus cholesterol (0.8 g/kg) or casein for four weeks. Subsequently for a period of six weeks, some of the rabbits were transferred to diets containing soy protein while others continued to receive the hypercholesterolaemic diets to which was added a mixture of amino acids (g/kg feed; glycine, 3.9; arginine, 6.9 and alanine, 1.6). Such additions increased the concentration of these amino acids in the casein diet to that in the hypocholesterolaemic soy protein diet. The cholesterol levels in the serum of the rabbits transferred to the soy protein diets declined rapidly, becoming significantly different from animals remaining on the hypercholesterolaemic diets after only three days. Serum cholesterol levels comparable to those in rabbits fed soy protein throughout the entire experiment were reached after about two weeks. The addition of the amino acids tended to reduce the concentration of cholesterol in the serum of the rabbits made hypercholesterolaemic by feeding the diets containing either casein or cholesterol. However, the effect reached significance only with the diet containing casein to which amino acids were added and then only at one time point. Six weeks after the cholesterol-fed animals were transferred to the cholesterol-free soy protein diet or to the diet containing the additional amino acids, apo E disappeared from the IDL1 (1.006 less than d less than 1.012 g/ml) and IDL2 (1.012 less than d less than 1.019 g/ml) fractions, but not from the VLDL fraction. Both with the cholesterol-free soy protein diet and the cholesterol diet fortified with amino acids, cholesterol in the VLDL fraction was reduced to values seen in animals fed the soy protein diet throughout the entire experimental period. The amount of cholesterol in the IDL and LDL fractions was decreased only in the soy protein group. Replacement of casein by soy protein, or the addition of amino acids to the casein diet did not induce the disappearance of apo E from the IDL or VLDL fractions. Only the soy protein diet lowered the amount of cholesterol in the VLDL and LDL fractions appreciably. It is concluded that the amount of apo E present in both IDL and VLDL does not invariably correlate with the level of serum cholesterol in rabbits. This study also indicates that the hypercholesterolaemic nature of casein resides only partially in the fact that it contains relatively low proportions of glycine, alanine and arginine compared with soy protein.

Amino Acids↗
PubMed1998

Cellular immune responses to beta casein: elevated in but not specific for individuals with Type I diabetes mellitus.

Elevated cellular immune responses against the cows' milk protein beta casein have been reported in individuals with Type I diabetes mellitus, a finding supportive of the concept that cows' milk consumption may be causative for the disease. We analysed cellular immune reactivities against beta casein in newly-diagnosed Type I diabetic patients, their immediate autoantibody negative relatives, and unrelated healthy individuals in order to further elucidate the role of anti-beta casein immunity in the pathogenesis of Type I diabetes mellitus. Peripheral blood mononuclear cells were stimulated in vitro with various concentrations of three different beta casein preparations, control antigens (tetanus toxoid, mumps extract) and a mitogen (phytohemagglutinin). The frequency and/or mean simulation index of cellular proliferation against two of the beta casein preparations at high antigen concentrations (i.e. 10 or 50 microg/ml) were significantly higher in newly-diagnosed Type I diabetic subjects compared with autoantibody negative healthy control subjects. However, reactivities against beta casein in the Type I diabetic probands and their autoantibody negative relatives, individuals with a very low-rate of disease development, were almost identical. Cellular immune reactivities to other antigens were similar between the subject groups. In addition to indicating the need for appropriately matched subject populations (e.g. human leukocyte antigen (HLA) matched relatives) when analysing cellular immune responses, these findings support our previous contention that individuals genetically prone to autoimmunity may be deficient in forming tolerance to dietary antigens. However, the significance of anti-beta casein immunity as a specific causative factor in the pathogenesis of Type I diabetes mellitus remains unclear.

Adolescent↗
PubMed2003

Suppression of beta-casein gene expression by inhibition of protein synthesis in mouse mammary epithelial cells is associated with stimulation of NF-kappaB activity and blockage of prolactin-Stat5 signaling.

The protein synthesis inhibitor cycloheximide (Chx) suppresses prolactin-induced beta-casein gene expression in the mammary epithelial cell line COMMA-D. As the mechanism underlying this effect is unclear, the effects of protein synthesis inhibitors on interactions of transcription factors with the beta-casein promoter were examined. Suppression of prolactin-induced beta-casein gene expression occurred in both COMMA-D cells and primary mammary cell cultures with as little as 2 h protein synthesis inhibition. This was associated with changes in transcription factors interacting at a response element in the proximal region of the rat beta-casein promoter. Inhibition of protein synthesis was associated with NF-kappaB binding at a site immediately 3' to the Stat5-binding site at position 97-89 of the beta-casein promoter, suppression of Stat5 DNA-binding activity, and inhibition of Stat5 tyrosine phosphorylation. Treatment with the NF-kappaB inhibitor parthenolide failed to restore prolactin responsiveness. These results show that protein synthesis inhibition is associated with both blockage of prolactin-Stat5 signaling and NF-kappaB binding to the beta-casein promoter, but that the latter is not necessary for the suppression of beta-casein expression.

Animals↗
PubMed1983

Phosphorylation of troponin and myosin light chain by cAMP-independent casein kinase-2 from rabbit skeletal muscle.

Casein kinase-2 from rabbit skeletal muscle was found to phosphorylate, in addition to glycogen synthase, troponin from skeletal muscle, and myosin light chain from smooth muscle. Troponin T and the 20,000 Mr myosin light chain are phosphorylated by casein kinase-2 at much greater rates than glycogen synthase. The V values for the phosphorylation of troponin and myosin light chain are nearly an order of magnitude greater than that of glycogen synthase; however, the Km values for these two substrates are greater than that for glycogen synthase. The kinase activities with the various protein substrates are stimulated approximately three- and fivefold by 5 mM spermidine and 3 mM spermine, respectively. Heparin is a potent inhibitor of the kinase when casein, glycogen synthase, or myosin light chain is the substrate. However, with troponin as substrate the kinase is relatively insensitive to inhibition by heparin. The amount of heparin required for 50% inhibition with troponin as substrate is at least 10 times greater than with casein as substrate. The phosphorylation of troponin by casein kinase-2 results in the incorporation of phosphate into two major tryptic peptides, which are different from those phosphorylated by casein kinase-1. The site in myosin light chain phosphorylated by casein kinase-2 is different from that phosphorylated by myosin light chain kinase.

Animals↗
PubMed1992

Effects of cationic polypeptides on the activity, substrate interaction, and autophosphorylation of casein kinase II: a study with calmodulin.

The effects of basic polypeptides on the ability of casein kinase II to phosphorylate an exogenous substrate (calmodulin) are correlated with steady-state autophosphorylation of the alpha- and beta-subunits of casein kinase II. Polylysine and polyarginine increase autophosphorylation of the alpha-subunit with a concomitant decrease in beta-subunit phosphorylation, while enhancing casein kinase II-stimulated phosphorylation of calmodulin over 100-fold. The highly basic carboxyl terminal segment of the endogenous p21c-Ki-ras has similar effects on the phosphorylation of calmodulin and the alpha- and beta-subunits of casein kinase II. Altering the concentration of cationic polypeptides produces a biphasic effect on the phosphorylation of both calmodulin and the alpha-subunit, which correlate positively with each other but do not correlate with beta-subunit phosphorylation. When the KCl concentration is changed, casein kinase II activity correlates positively only with alpha-subunit phosphorylation. In contrast, the biphasic response of calmodulin phosphorylation by casein kinase II at different Ca2+ concentrations correlates positively with both alpha- and beta-subunit phosphorylation. Therefore, in the presence of basic protein activators, the rate of phosphorylation of a substrate, calmodulin, correlates with steady-state phosphorylation of the alpha-subunit, but not with the beta-subunit under all conditions tested. Endogenous cationic factors may modulate the in vivo activity of casein kinase II and alter the interaction of the enzyme with specific intracellular substrates.

Animals↗
PubMed1986

Secretion of cholesteryl-ester-rich lipoproteins by the perfused livers of rabbits fed a wheat-starch-casein diet.

Rabbits fed a cholesterol-free semi-synthetic wheat-starch-casein diet had a high plasma cholesterol concentration; most of the cholesterol was associated with low-density lipoproteins (LDL). Chemical analyses of plasma lipoproteins revealed that very-low-density lipoproteins (VLDL), intermediate lipoproteins and LDL from casein-fed rabbits contained more cholesteryl ester than that of lipoproteins isolated from chow-fed animals. The fatty acid composition of cholesteryl esters of plasma lipoproteins showed that there were higher contents of oleic acid than linoleic acids in lipoproteins from casein-fed rabbits. Lipoproteins isolated from liver perfusates of casein-fed rabbits had higher cholesteryl oleate content than lipoproteins from chow-fed rabbit liver perfusates. There was a marked increase in secretion of apolipoproteins from perfused livers of casein-fed rabbits. We conclude that the high levels of plasma cholesterol in casein-fed rabbits are of hepatic origin and that one of the hypercholesterolemic actions of dietary casein in rabbits is the induction of hepatic synthesis and secretion of cholesteryl-ester-rich lipoproteins.

Animals↗
PubMed1977

Interaction of sodium dodecyl sulfate and of non-ionic detergents with S-carboxyamidomethyl-k-casein.

Sodium dodecyl sulfate binds to S-carboxyamidomethyl-k-casein in a highly cooperative manner at a concentration near the critical micelle concentration, showing a strong dependence on ionic strength. The maximum number of sodium dodecyl sulfate molecules bound is attained above the critical micelle concentration, and is very close to the micelle aggregation number in the absence of protein. The binding sites on the protein for sodium dodecyl sulfate are localized mainly on para-k-casein part, which is a hydrophobic fragment of k-casein produced by rennin attack. The mode of the action of sodium dodecyl sulfate on S-carboxyamidomethyl-k-casein resembles that of several integral membrane proteins, rather than of water soluble proteins. On considering possible situations, it is suggested that the unusual interaction of S-carboxyamidomethyl-k-casein with sodium dodecyl sulfate is responsible for an anomalous migration of reduced k-casein observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Further, the suggestion was made by the binding studies of sodium dodecyl sulfate and non-ionic detergents that the sites which were involved in self-association of S-carboxyamidomethyl-k-casein participated in the binding sites of detergents.

Caseins↗
PubMed1992

Iron oxidation by casein.

Casein accelerates the oxidation of Fe(II) to Fe(III) and the resulting Fe(III) remains strongly bound to the casein. Removal of phosphate from the casein abolishes the oxidative process. The oxidation rate is proportional to the casein concentration, and with high casein concentrations the rate is pseudo-first-order with respect to Fe(II) with a half-life of approximately 2 minutes. The oxidized iron is stoichiometrically bound to the casein, each mg of casein binding approximately 10 micrograms of iron. The physiological significance is discussed.

Animals↗
PubMed1990

In vitro and in vivo growth and casein gene expression of mouse mammary tumor epithelial cells in response to hormones.

Cells from autochthonous mouse mammary carcinomas which display estrogen-independent growth in vivo were studied for their hormonal responses in primary culture. A culture system employing insulin-supplemented, serum-free medium and basement membrane Matrigel as a substratum was used to cultivate tumor cells. The cells did not exhibit in vitro estrogen- or prolactin-dependent growth. Primary tumors still displayed a constitutional expression of alpha-, beta-, and gamma-casein mRNAs. These messages were dramatically reduced during the culture period. However, seven to eightfold increases in alpha- and beta-casein mRNAs were inducible in the 5-day cultures by treatment with prolactin and hydrocortisone. If the hormones were present through a 2-week culture period, the levels of alpha-, beta-, and gamma-casein mRNAs in the cells were maintained and displayed in a time-dependent increase with a peak at 10-14 days. The accumulation of beta-casein mRNA in vitro did not require DNA synthesis. Administration of prolactin directly into the growing tumors in vivo could also enhance beta-casein mRNA levels in the tumor cells. Morphological studies of the cells cultured in the presence of prolactin and hydrocortisone did not reveal visible changes compared with those without hormonal treatment. Transplantation of tumor cells cultured in the presence or absence of hormones resulted in the development of tumors in mice at approximately the same time. The current studies suggest that the autochthonous mammary tumor cells, independent of estrogen for cell growth, were still inducible for casein gene expression in vitro and in vivo by appropriate hormones. The induction and maintenance of casein messages by a single hormonal treatment did not appear to correlate with morphology and DNA synthesis of cells in vitro or with tumor-producing capacities in vivo.

Adenocarcinoma↗
PubMed1987

The phosphorylation of nucleoplasmin by casein kinase-2 is resistant to heparin inhibition.

Highly purified preparations of casein kinase-2 from the nuclei of Xenopus laevis oocytes and from calf thymus can phosphorylate in vitro purified nucleoplasmin from X. laevis oocytes and eggs. The phosphorylation of nucleoplasmin by both kinase preparations is quite insensitive to heparin in contrast with casein phosphorylation which is completely abolished by heparin concentrations above 10 micrograms/ml. However, the phosphorylation of nucleoplasmin and casein are inhibited in a very similar fashion by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a well characterized specific inhibitor of casein kinase-2. Similarly, nucleoplasmin phosphorylation by the oocyte enzyme can be stimulated several-fold by spermine, another characteristic of this enzyme. These findings indicate that the phosphorylation of nucleoplasmin by purified casein kinase-2, while showing typical response to DRB and spermine, exhibits anomalous behavior in its resistance to heparin inhibition. It is possible that the large clusters of acidic amino acids in nucleoplasmin permit this substrate to interact with the enzyme more efficiently than other protein substrates. Heparin is generally considered a potent and specific inhibitor of casein kinase-2. This study, however, questions the validity of utilizing heparin inhibition as a criterion for casein kinase-2 involvement.

Animals↗
PubMed1985

Casein-induced hypercholesterolaemia in rabbits is calcium-dependent.

Young male rabbits were fed semi-purified diets containing either casein or soy protein, both at a normal (0.84%, w/w) and a high (1.44%, w/w) level of dietary calcium. At the normal calcium level, casein, as compared with soy protein, increased the concentration in serum of total and free cholesterol and the ratio of free cholesterol to phospholipid. Also, casein increased the intestinal phosphate absorption and decreased the faecal fat excretion. The hypercholesterolaemic response of the rabbits on the casein diet was significantly correlated with both phosphate absorption (r = +0.744) and fat excretion (r = -0.701). The increased amount of dietary calcium inhibited the casein-specific effects on both the intestinal and the serum lipid parameters. In contrast, calcium did not change these parameters in rabbits fed the soy protein diet. These results support the hypothesis that the degree of phosphorylation of casein is involved in the mechanism of the casein-induced hypercholesterolaemia by means of its effect on the enterohepatic cycle of bile acids.

Animals↗
PubMed1983

Reversibility of the phosphate transfer between ATP and phosphoproteins catalysed by a cyclic nucleotide independent (G type) casein kinase.

Purified casein kinase G was found able to catalyse the synthesis of [gamma-32P]ATP in the presence of ADP, phosphocasein (previously 32P-labeled by the forward kinase reaction) and magnesium. Apparent Km values of approx. 0.5 mM for phosphocasein and 7.5 mM for ADP were calculated, these values indicating low affinities for the substrates as compared to those exhibited for casein and ATP in the forward reaction. The reverse casein kinase G activity appeared to prefer ADP and GDP as phosphate acceptors. Whereas the casein kinase G reverse reaction could be supported by casein, phosvitin and histone previously phosphorylated by the enzyme, the same proteins could not serve as a phosphate source when previously phosphorylated by the cAMP-dependent protein kinase. Forward and reverse casein kinase G reactions exhibited different optimal pH values (8.5 and 7.2, respectively) and a different sensitivity to Mg2+. Spermine, which activated the kinase activity, blocked the reverse reaction at millimolar concentrations. Although the biological significance of the casein kinase G reverse activity remains to be assessed in intact cell, the process may be useful as a tool in the characterization of phosphorylatable sites in phosphoproteins.

Adenosine Diphosphate↗
PubMed1988

Casein kinase II accumulation in the nucleolus and its role in nucleolar phosphorylation.

A rabbit antiserum against highly purified casein kinase II from mouse tumor cells was used for immunolocalization of the enzyme in fixed, permeabilized mouse cells. Casein kinase II was highly accumulated in nucleoli compared to the extra-nucleolar space of the nucleus or to the cytoplasma. Casein kinase II samples highly purified from the cytoplasma, from the extra-nucleolar fraction of the nucleus or from nucleoli exhibited no differences with respect to structure and function. All samples originally had an alpha 2 beta 2 structure (alpha, 42 kDa; beta, 24 kDa) showing formation of the alpha'-chain (36 kDa) only in the late steps of purification. The isoelectric point of the alpha-chain of all three samples was pH 7.7 and that of the beta-chain was pH 6.4-6.6. Using ATP or GTP, all three casein kinase II samples gave the same results of maximum phosphorylation of purified nucleolar marker phosphoproteins pp105/C23, pp135 and B23, yielding pp135 as one of the most highly phosphorylated proteins with an incorporation of about 75 phosphate groups per molecule pp135. Studies on optimum conditions of phosphorylation of nucleolar phosphoproteins by casein kinase II revealed that each of the protein substrates individually responded to alterations of assay parameters such as pH, magnesium ion and sodium chloride concentrations indicating that predominantly individual structural criteria were responsible for optimum phosphorylation. The determination of the apparent Km of casein kinase II for purified nucleolar phosphoproteins yielded values of 0.15 microM (pp105/C23), 0.1 microM (pp135) and 1.0 microM (B23) identifying them as high-affinity substrates of casein kinase II.

Animals↗
PubMed1990

Long-term oral branched-chain amino acid treatment in chronic hepatic encephalopathy. A randomized double-blind casein-controlled trial. The Italian Multicenter Study Group.

In a double blind randomized study, branched-chain amino acids and placebo (casein) were compared as a treatment for chronic hepatic encephalopathy in cirrhosis. After a 15-day run-in period with controlled diet (45-65 g protein), the patients were administered, in addition to their diet, branched-chain amino acids (0.24 g/kg, 30 patients) or an equinitrogenous amount of casein (34 patients). One patient on branched-chain amino acids and two on casein were lost to the study. After 3 months, the index of portal-systemic encephalopathy significantly improved in patients on active treatment (from 40 [S.D. 14]% to 21 [17]), but was not in subjects receiving casein (from 37 [13]% to 36 [12]). Two or more parameters of the index improved in 24 patients treated with amino acids (80%; confidence limits, 61-92%), and only in 12 receiving casein (35%; confidence limits, 20-54%; p less than 0.001). Patients who did not improve were given an alternative treatment for 3 more months. Casein-treated patients given branched-chain amino acids rapidly improved. The changes in neuropsychologic function were associated with an improvement in semiquantitative nitrogen balance, which became consistently positive in amino acid-treated subjects; there was also a mild improvement in nutritional parameters and in liver function tests. The supplementation of oral branched-chain amino acids to the diet is superior to casein as a treatment for providing adequate nitrogen supply and improving the mental state of cirrhotic patients with chronic encephalopathy.

Adult↗
PubMed1980

Effects of lysomotropic agents, and of microfilament- and microtubule-disrupting drugs on the activation of casein-gene expression by prolactin in the mammary gland.

The organ-culture technique was used to investigate the effects of lysomotropic agents (NH4Cl and chloroquine) and of modifiers of microfilaments (cytochalasin B) and microtubules (colchicine) on the induction of casein synthesis and the accumulation of casein mRNA by prolactin in the rabbit mammary gland. Neither chloroquine nor NH4Cl altered the lactogenic action of prolactin. Cytochalasin B attenuated the response to prolactin in terms of casein synthesis. However, this drug did not hamper the accumulation of casein mRNA. Colchicine exhibited a marked specific inhibitory effect on the induction of casein synthesis. It also prevented the accumulation of casein mRNA. These results suggest that a putative degradation of the internalized prolactin--receptor complex by lysosomes is not strictly involved in prolactin action. In addition, the integrity of the microfilaments seems unnecessary in the process of casein-gene activation by prolactin. By contrast, the integrity of the microtubule network seems absolutely necessary to ensure the transmission of prolactin information to the nucleus.

Ammonium Chloride↗