Changes in protein kinase activities in lamb adrenals at late gestation and early postnatal stages

Protein kinase CK2 ("casein kinase-2") and its implication in cell division and proliferation

Protein kinase CK2 (also termed casein kinase-2 or -II) is a ubiquitous Ser/Thr-specific protein kinase required for viability and for cell cycle progression. CK2 is especially elevated in proliferating tissues, either normal or transformed, and the expression of its catalytic subunit in transgenic mice is causative of lymphomas. CK2 is highly pleiotropic: more than 160 proteins phosphorylated by it at sites specified by multiple acidic residues are known. Despite its heterotetrameric structure generally composed by two catalytic (alpha and/or alpha') and two non catalytic beta-subunits, the regulation of CK2 is still enigmatic. A number of functional features of the beta-subunit which could cooperate to the modulation of CK2 targeting/activity will be discussed.

The effect of isobutylmethylxanthine, forskolin, and cholera toxin on growth hormone release from pituitary cell cultures of perinatal and mature rats

The factors that regulate growth hormone (GH) release during the perinatal period are not well understood. Circulating GH levels are markedly elevated in mammalian fetuses and newborns compared with mature animals, and the immature pituitary is highly responsive to the GH-stimulatory effect of GH-releasing factor (GHRF). The etiology of these developmental changes in GH secretion is not known. In order to investigate the mechanisms underlying GH release from immature pituitaries, we tested the effects of agents that increase intracellular cyclic adenosine 3',5' monophosphate (cAMP) production independent of the GHRF receptor on GH release from pituitaries of developing and mature rats. Pituitary cell cultures from fetal (day 20 of gestation), newborn (postnatal day 2), juvenile (postnatal day 12-15), adult male (3-4 months), and adult female (3-4 months) rats were tested with isobutylmethylxanthine (IBMX; 0.001-1.0 mM), forskolin (0.01-10 microM), and cholera toxin (0.025-25 ng/ml). IBMX, forskolin, and cholera toxin stimulated GH release in a dose-dependent manner from pituitary cultures of all age groups. However, the magnitude of the GH responses to these agents was highly age-dependent. Perinatal pituitaries exhibited markedly greater GH responses to IBMX, forskolin, and cholera toxin than did those of mature animals (P < 0.001 for age effect with each agent). GH release in response to the highest dose of IBMX (1 mM) was 301 +/- 8, 389 +/- 37, 296 +/- 33, 198 +/- 14, and 187 +/- 19% of control values from pituitary cell cultures of fetal, newborn, juvenile, adult male, and adult female rats, respectively (P < 0.001). In response to the highest dose of forskolin (10 microM) GH release was 537 +/- 46, 601 +/- 75, 274 +/- 22, 270 +/- 37, and 248 +/- 35% of control values in the same respective age groups (P < 0.001). Similarly, the highest dose of cholera toxin (25 ng/ml) stimulated GH release to 407 +/- 55, 365 +/- 43, 249 +/- 26, 186 +/- 11, and 186 +/- 1% of controls in these respective age groups (P < 0.003). The marked stimulation of GH release from perinatal pituitaries by IBMX, forskolin, and cholera toxin is consistent with the concept that cAMP is a potent mediator of GH release from immature as well as mature somatotrophs. The developmental changes in the GH secretory response to these agents further suggest that signal transduction pathways mediating GH release may undergo maturation, at least in part, at intrasomatotroph loci distal to the GHRF receptor.

Ontogenesis of cholesterol side-chain cleavage activity in the ovine adrenal during late gestation

The present study examined the activity of the cholesterol side-chain cleavage system, and the amount of cytochrome P450scc in adrenal glands of sheep fetuses and newborn lambs as well as the in vitro regulation of these parameters. Freshly isolated fetal adrenal cells incubated in the presence of 1 mM 8Br-cAMP or 25 microM 22R-OH cholesterol, produced 4- to 5-fold less pregnenolone than neonatal cells under similar conditions. Likewise, pregnenolone production by isolated fetal adrenal mitochondria was lower than that of neonatal mitochondria when endogenous cholesterol was used as a substrate or when 22R-OH cholesterol was added to the incubation medium. Also, the amount of P450scc, determined by immunoblot, was lower in fetal mitochondria than in neonatal mitochondria. In culture, ACTH, despite enhancing both the production of pregnenolone and the incorporation of [14C]acetate in cholesterol and its end-products by fetal adrenal cells, neither increased the amount of pregnenolone formed from 22R-OH cholesterol nor the amount of immunoreactive P450scc. By contrast, during the first 48 h of culture under standard conditions, there was a "spontaneous" increase in the activity of P450scc which reached values observed in neonatal adrenal cells. Such a development was inhibited when 5% ovine fetal serum was added to the culture medium. These results reinforce the view that in the ovine fetal adrenal gland, the development of P450scc is not ACTH-dependent but involves most probably a decrease in inhibitory factors present in fetal blood.

Purification of casein kinase I and isolation of cDNAs encoding multiple casein kinase I-like enzymes

We have purified casein kinase I (CKI) over 6000-fold from bovine thymus and have sequenced seven tryptic peptides that account for nearly 25% of the primary sequence of the enzyme. By using PCR, partial cDNAs encoding CKI and a related enzyme (CKI-delta) were isolated. A product that may correspond to an alternatively spliced form of CKI was also detected. The CKI PCR product was used to probe a bovine brain cDNA library from which cDNAs corresponding to CKI (CKI-alpha) and two homologous enzymes (CKI-beta and CKI-gamma) were identified. The finding that there are at least four CKI-like enzymes suggests that CKI activity in tissues or cell extracts may be composed of multiple related but distinct protein kinases. This group of enzymes is not similar to any other known protein kinases and may, therefore, represent an additional branch of the protein kinase family.