On the tyrosine kinase mechanism of the novel effect of insulin and insulinlike growth factor I. Stimulation of the adenylyl cyclase system in muscle tissues

Prenatal cocaine alone and combined with nicotine alters ANG II and IGF-1 induced left atrial contractions in aging male offspring

Prenatal cocaine or nicotine affects inotropic activity in the hearts of rat offspring. However, the long-term consequence of this exposure on the cardiac response to hormonal challenge is unknown. We assessed the inotropic effects of angiotensin II (ANG II) and insulin-like growth factor 1 (IGF-1) in the left atria of 19.0-24.5 month-old male rats exposed on gestation days 8-21 to 1 of 6 treatments: low cocaine (LC) (20 mg/kg) or high cocaine (HC) (40 mg/kg); 20 mg/kg cocaine and high nicotine (5 mg/kg nicotine) (LC/HN); 40 mg/kg cocaine and low nicotine (2.5 mg/kg nicotine) (HC/LN); pair fed: yoked to HC (PF); saline: injection of 0.9% NaCl (SAL). Isometric contractions were assessed by electrical stimulation of isolated left atria superfused with Tyrode solution (control) to which ANG II (10-7 mol/L, 20 min) and IGF-1 (10-8 mol/L, 20 min) in the presence of ANG II were added sequentially. Offspring in all cocaine groups showed a higher peak tension development (PTD) to ANG II than PF controls. This increase in PTD was attenuated by subsequent addition of IGF-1 in all except HC offspring. However, with the HC/LN combination the IGF-1 effect on PTD was again evident. The velocities of contraction and relaxation were positively affected by ANG II only in the combined prenatal drug groups; IGF-1 reduced only contraction velocity. Our data demonstrate that IGF-1 reverses the positive inotropic effect of ANG-II in atrial muscle of aging rats and that gestational exposure to only high doses of cocaine eliminates this protective response. It appears that combined prenatal exposure to cocaine and nicotine does not exacerbate the decline in cardiac function and responsiveness to inotropic drugs seen in the aging heart.

Role of phosphatidylinositol-3-kinase and protein kinase C zeta in the adenylate cyclase signal mechanism of action of relaxin in muscle tissues of rats and mollusks

We showed that phosphatidylinositol-3-kinase and protein kinase C zeta are involved in the adenylate cyclase signal mechanism of relaxin action. A selective inhibitor of phosphatidylinositol-3-kinase wortmannin blocked the stimulatory effect of relaxin on adenylate cyclase in rat skeletal muscles and Anodonta cygnea smooth muscles. Antibodies against protein kinase C zeta abolished the relaxin-induced stimulation of adenylate cyclase in rat muscles, but not in mollusk muscles. Our results indicate that phosphatidylinositol-3-kinase and protein kinase C zeta play a role in the adenylate cyclase signal mechanism of relaxin action.

Comparative study of biological activity of insulins of lower vertebrates in the novel adenylyl cyclase test-system

The biological activity of insulins of lower vertebrates (teleosts-Oncorhynchus gorbuscha, Scorpaena porcus, chondrosteans-Acipenser guldenstaedti and cyclostomates-Lamperta fluviatilis) was studied and compared with that of standard pig insulin. The determination of biological activity was made using the novel adenylyl cyclase (AC) test-system based on the adenylyl cyclase signaling mechanism (ACSM) of insulin action discovered earlier by the authors. The biological activity of insulins was estimated as EC(50), i.e. concentration leading to half-maximal activating effect of the hormone (10(-11)-10(-7) M), in vitro, on adenylyl cyclase in two types of the target tissues: in membrane fractions of the muscles of rat and mollusc Anodonta cygnea. In rat, the efficiency of insulins was found to decrease in the following order: pig insulin>scorpaena insulin>gorbuscha insulin>sturgeon insulin>lamprey insulin. In the mollusc, the order was different: sturgeon insulin>scorpaena insulin>pig insulin>gorbuscha insulin. Lamprey insulin at the same concentrations did not apparently reach the maximal adenylyl cyclase activating effect. The suggestion was made that differences in the biological activity of insulins depend on the hormone structure and a number of indexes characteristic of the adenylyl cyclase test-system in the vertebrate and invertebrate tissues. The proposed adenylyl cyclase test-system is highly sensitive to insulin at physiological concentrations, has good reproduction and is easy to apply.

A novel view on the mechanisms of action of insulin and other insulin superfamily peptides: involvement of adenylyl cyclase signaling system

A new signaling mechanism common to mammalian insulin, insulin-like growth factor I, relaxin and mollusc insulin-like peptide, and involving receptor-tyrosine kinase==>G(i) protein (betagamma)==>phosphatidylinositol-3-kinase==>protein kinase Czeta==>adenylyl cyclase==>protein kinase A was discovered in the muscles and some other tissues of vertebrates and invertebrates. The authors' data were used to reconsider the problem of participation of the adenylyl cyclase-cAMP system in the regulatory effects of insulin superfamily peptides. A hypothesis has been put forward according to which the adenylyl cyclase signaling mechanism producing cAMP has a triple co-ordinating role in the regulatory action of insulin superfamily peptides on the main cell processes, inducing the mitogenic and antiapoptotic effects and inhibitory influence on some metabolic effects of the peptides. It is suggested that cAMP is a key regulator responsible for choosing the transduction pathway by concerted launching of one (proliferative) program and switching off (suppression) of two others, which lead to cell death and to the predomination of anabolic processes in a cell. The original data obtained give grounds to conclude that the adenylyl cyclase signaling system is a mechanism of signal transduction not only of hormones with serpentine receptors, but also of those with receptors of the tyrosine kinase type (insulin superfamily peptides and some growth factors).

A dual role of protein kinase C in insulin signal transduction via adenylyl cyclase signaling system in muscle tissues of vertebrates and invertebrates

Further decoding of a novel adenylyl cyclase signaling mechanism (ACSM) of the action of insulin and related peptides detected earlier (Pertseva et al. Comp Biochem Physiol B Biochem Mol Biol 1995;112:689-95 and Pertseva et al. Biochem Pharmacol 1996;52:1867-74) was carried out with special attention given to the role of protein kinase C (PKC) in the ACSM. It was shown for the first time that transduction of the insulin signal via the ACSM followed by adenylyl cyclase (AC, EC 4.6.1.1) activation was blocked in the muscle tissues of rat and mollusc Anodonta cygnea in the presence of pertussis toxin, inducing the impairment of G(i)-protein function, wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3-K), and calphostin C, a blocker of PKC. The cholera toxin treatment of muscle membranes led to an increase in basal AC activity and a decrease in enzyme insulin reactivity. Phorbol ester and diacylglycerol activation of PKC (acute treatment) induced the inhibition of the insulin AC activating effect. This negative influence was also observed in the case of the AC system activated by biogenic amines. It was first concluded that the ACSM of insulin action involves the following signaling chain: receptor tyrosine kinase => G(i) (betagamma) => PI3-K => PKCzeta (?) => G(s) => AC => adenosine 3',5'-cyclic monophosphate. It was also concluded that the PKC system has a dual role in the ACSM: (1) a regulatory role (PKC sensitive to phorbol esters) that is manifested as a negative feedback modulation of insulin signal transduction via the ACSM; (2) a transductory role, which consists in direct participation of atypical PKC (PKCzeta) in the process of insulin signal transduction via the ACSM.

Insulin NO-dependent action on airways smooth muscles

In order to find out how insulin acts on airway smooth muscle and which mechanisms could be involved, we studied the effect of insulin on contraction induced, first, by KCl and, second, by Acetylcholine (Ach), before and after epithelium removal, and finally in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor. Tracheal smooth muscle strips from 24 rabbits, 6 being used for each experiment. Each muscle strip was pretreated with a solution containing either 80 mM KCl or 10(-5) Ach and increasing doses of insulin (range 10(-10)--10(-5) M) in the presence or absence of 10(-4) M L-NAME. A reference curve for contraction evoked by 80 mM KCl or 10(-5) M Ach in the presence or absence of 10(-4) M L-NAME was recorded each time before the pretreatment mentioned above. Insulin evoked a concentration-dependent inhibition of tracheal smooth muscle contraction, induced by 80 mM KCl or 10(-5) M Ach. After epithelium removal, insulin (10(-8), 10(-7) M) evoked statistically significant increases to the contractions induced by 10(-5) M Ach compared to the contractions induced by 10(-5) M Ach and insulin in the presence of epithelium (P < 0.05). These increases were higher when 10(-4) M l-NAME was added to the bath (P < 0.05). In conclusion, these results indicate that insulin inhibits tracheal smooth muscle contraction by acting on epithelium and releasing NO.

Insulin-like growth factor inhibits vascular contraction to 5-hydroxytryptamine: involvement of tyrosine phosphatase

This study tests the hypothesis that insulin-like growth factor 1 (IGF-1)-induced vasodilation is due to the stimulation of tyrosine phosphatase. Rat aortic segments (endothelium intact) were placed in muscle baths for force measurement. Segments were contracted to serotonin [5-hydroxytyptamine (5-HT), 10(-7)-10(-5) M] before and after incubation with IGF-1 (10-100 nM; 90 min). IGF-1 caused a 20% inhibition of 5-HT-induced contractions. This inhibition was reversed by the tyrosine phosphatase inhibitors sodium orthovanadate and molybdate. Orthovanadate did not alter inhibitory properties of the calcium channel antagonist verapamil, suggesting that the phosphatase inhibitors were relatively specific. IGF-1-induced inhibition was not altered by blockade of nitric oxide synthase. Western blot analysis confirmed that the 5-HT-induced stimulation of tyrosine phosphorylation of the 42-kDa extracellular signal-regulated mitogen-activated protein kinase protein was reduced by IGF-1 (52% inhibition), an inhibition that was attenuated by orthovanadate. These data are consistent with the hypothesis that the vasodilator activity of IGF-1 is mediated by the activation of a tyrosine phosphatase.

Insulin stimulates Mg2+ uptake in mouse distal convoluted tubule cells

Insulin has been shown to be a magnesium-conserving hormone acting, in part, through stimulation of magnesium absorption within the thick ascending limb. Although the distal convoluted tubule possesses the most insulin receptors, it is unclear what, if any, actions insulin has in the distal tubule. The effects of insulin were studied on immortalized mouse distal convoluted tubule (MDCT) cells by measuring cellular cAMP formation with radioimmunoassays and Mg2+ uptake with fluorescence techniques using mag-fura 2. To assess Mg2+ uptake, MDCT cells were first Mg(2+) depleted to 0.22 +/- 0.01 mM by culturing in Mg2+-free media for 16 h and then placed in 1.5 mM MgCl2, and the changes in intracellular Mg2+ concentration ([Mg2+]i) were measured with microfluorescence. [Mg2+]i returned to basal levels, 0.53 +/- 0.02 mM, with a mean refill rate, d([Mg2+]i)/dt, of 164 +/- 5 nM/s. Insulin stimulated Mg2+ entry in a concentration-dependent manner with maximal response of 214 +/- 12 nM/s, which represented a 30 +/- 5% increase in the mean uptake rate above control values. This was associated with a 2.5-fold increase in insulin-mediated cAMP generation (52 +/- 3 pmol. mg protein(-1). 5 min(-1)). Genistein, a tyrosine kinase inhibitor, diminished insulin-stimulated Mg2+ uptake (169 +/- 11 nM/s), but did not change insulin-mediated cAMP formation (47 +/- 5 pmol. mg protein(-1). 5 min(-1)). PTH stimulates Mg2+ entry, in part, through increases in cAMP formation. Insulin and PTH increase Mg2+ uptake in an additive fashion. In conclusion, insulin mediates Mg2+ entry, in part, by a genistein-sensitive mechanism and by modifying hormone-responsive transport. These studies demonstrate that insulin stimulates Mg2+ uptake in MDCT cells and suggest that insulin acts in concert with other peptide and steroid hormones to control magnesium conservation in the distal convoluted tubule.

Regulation of insulin-like growth factor-binding protein-5 expression during Schwann cell differentiation

We have reported that immortalized Schwann cells (SC) express the insulin-like growth factor I receptor and IGF-binding protein-5 (IGFBP-5). IGF-I promotes SC survival and protects IGFBP-5 in SC-conditioned medium from proteolysis. In the current study we examined the roles of IGF-I and IGFBP-5 in primary SC. IGF-I enhances primary SC differentiation and gene and protein expression of IGFBP-5 and the myelinating protein, P0. SC that stably overexpress human IGFBP-5 also have higher levels of P0 gene expression. The phosphatidylinositol-3 kinase inhibitor (LY294002), but not the mitogen-activated protein kinase kinase inhibitor (PD98059), blocks IGF-I enhancement of IGFBP-5 gene and protein expression. Collectively, these results suggest that IGF-I promotes SC differentiation, and this may occur in part by enhancing IGFBP-5 expression via phosphatidylinositol-3 kinase activation. These data support a link between enhanced IGFBP-5 expression and cellular differentiation.

Soybean isoflavones, genistein and genistin, inhibit rat myoblast proliferation, fusion and myotube protein synthesis

The isoflavones, genistein and genistin, are cytotoxic in vitro (e.g. , inhibition of cell proliferation), due in part to inhibition of protein tyrosine kinase and DNA topoisomerase activities. Normal cell functions associated with these enzymatic activities could potentially be impaired in animals through ingestion of soybean products. In this study, cultured rat myogenic cells (L8) were used to determine whether genistein or genistin influences myoblast proliferation and fusion, and myotube protein synthesis and degradation. Genistein or genistin was dissolved in dimethylsulfoxide and included in the culture medium at 0, 1, 10 or 100 micromol/L. Myoblast proliferation was measured by methyl-3H-thymidine incorporation over 48 h. Myoblast differentiation was evaluated by the number of nuclei in multinucleated myotubes. Myotube protein synthesis was measured by 2-h 3H-amino acid incorporation into the myosin and total protein pools after acute (2 h) or chronic (24 h) exposure to similar treatments; protein degradation was measured by measuring radioactivity in protein pools following a time course of protein breakdown after myotube proteins were prelabeled with 3H-amino acids. Genistein or genistin strongly inhibited in vitro myoblast proliferation (P < 0.001) and fusion (P < 0.001) in a dose-dependent manner with effective genistein concentration as low as 1 micromol/L. Genistein or genistin inhibited protein accretion in myotubes (P < 0.001). Decreased protein accretion is largely a result of inhibition on cellular (myofibrillar) protein synthesis rate. No adverse effect on protein degradation was observed. Results suggest that if sufficient circulating concentrations are reached in tissues of animals consuming soy products, genistein/genistin can potentially affect normal muscle growth and development.

On the mechanism of relaxin action: the involvement of adenylyl cyclase signalling system

The molecular mechanism of relaxin action was studied taking into account the evolutionary relationship of the peptides belonging to the insulin superfamily and using the authors' previous data on the involvement of the adenylyl cyclase (AC) signalling system in the action of insulin and related peptides. Human relaxin 2 (10(-12)-10(-8) M) has been shown to cause a dose-dependent activating effect on AC in the human myometrium (+370%), in rat skeletal muscles (+117%) and the smooth foot muscles of the bivalve mollusc Anodonta cygnea (+73%). In these tissues mammalian insulin and insulin-like growth factor-1 (IGF-1) also had the AC activating effect. The order of efficiency of the above peptides based upon their ability to induce the maximal AC activating effect was as follows: relaxin > IGF-1 > insulin (human myometrium); IGF-1 > relaxin > insulin (rat skeletal muscle); molluscan insulin-like peptide > IGF-I > insulin > relaxin (molluscan muscle). The relaxin AC activating effect was inhibited with a selective tyrosine kinase blocker tyrphostin 47 and potentiated with Gpp[NH]p providing evidence for the participation of the receptor-tyrosine kinase and G-protein of the stimulatory type (Gs) in the regulatory action of relaxin. The conclusion is that the signalling chain: receptor tyrosine kinase ==> Gs protein ==> AC is involved in the mechanism of relaxin action.

Computer-assisted sperm motion analysis of bovine sperm treated with insulin-like growth factor I and II: implications as motility regulators and chemokinetic factors

The effects of insulin-like growth factors (IGFs) I and II on motility of bovine sperm were examined using a computer-assisted sperm motion analyzer (CASA). The following kinematic parameters were examined: percentage of rapidly moving cells, straight-line velocity , curvilinear velocity, average path velocity, amplitude of lateral head displacement, and beat cross frequency. Sperm were treated with IGF-I (100 ng/mL) or IGF-II (250 ng/mL) and compared to sperm in modified Tyrodes' medium only (control) at 90, 180, and 360 min using CASA. Insulin-like growth factor I and II increased the percentage of rapidly moving cells, straight-line velocity, curvilinear velocity, average path velocity, amplitude of lateral head displacement, and beat cross frequency compared to the control treatment. These results indicate that IGFs may be involved in initiation and maintenance of bovine sperm motility.

Endothelin-1 and insulin activate the steady-state voltage dependent R-type Ca2+ channel in aortic smooth muscle cells via a pertussis toxin and cholera toxin sensitive G-protein

In single rabbit aortic smooth muscle cells, and at a concentration known to induce a maximum sustained increase of intracellular Ca2+ via activation of the steady-state voltage dependent R-type Ca2+ channels, endothelin-1 (10(-7) M) and insulin (80 microU/ml) were found to induce a sustained increase in cytosolic free Ca2+ ([Ca]i) levels that was significantly attenuated by pre-treatment with either pertussis toxin (PTX), cholera toxin (CTX) or removal of extracellular Ca2+. However, both PTX and CTX failed to inhibit the sustained depolarization-evoked sustained Ca2+ influx and [Ca]i elevation via activation of the R-type Ca2+ channels. Moreover, ET-1 and insulin-evoked sustained increases in Ca2+ influx were not attenuated by the selective PKC inhibitor, bisindolylmaleimide (BIS), or the specific L-type Ca2+ channel blocker, nifedipine, but were completely reversed by the R-type Ca2+ channel blocker, (-) PN 200-110 (isradipine). These data suggest that both insulin and ET-1 activate the nifedipine-insensitive but isradipine-sensitive steady state voltage dependent R-type Ca2+ channels present on rabbit VSMCs and these channels are directly coupled to PTX and CTX sensitive G protein(s).