Cloning and sequencing of the cDNA encoding the avian kidney cAMP-dependent protein kinase inhibitor protein

The role of an endogenous PKA inhibitor, PKIalpha, in organizing left-right axis formation

Protein kinase inhibitor (PKI) is an endogenous inhibitor of cAMP-dependent protein kinase A (PKA). We have found that the alpha-isoform of PKI (PKIalpha) is asymmetrically expressed along the left-right (L-R) axis in chick embryos. At stage 6, PKIalpha is expressed on the right side of the node, and this asymmetric expression continues until stage 7+. After stage 8, PKIalpha expression returns symmetric. Treatment of embryos with antisense PKIalpha oligonucleotides increased the incidence of reversed heart looping. Antisense oligonucleotides also induced ectopic expression of the left-specific genes Nodal and Pitx2, and suppressed the expression of the right-specific gene SnR in the right lateral plate mesoderm. Similarly, treatment with PKA activators forskolin and Sp-cAMPs resulted in both reversed heart looping and bilateral expression of NODAL: Ectopic activin induced PKIalpha on the left side of the node, while ectopic Shh and anti-Shh antibody had no effect on PKIalpha expression. Taken together, these data suggest that PKIalpha induced by an activin-like molecule, through the inhibition of PKA activity, suppresses the Nodal-Pitx2 pathway on the right side of the body.

Genomic cloning, structure, and regulatory elements of the 1 alpha, 25(OH)2D3 down-regulated gene for cyclic AMP-dependent protein kinase inhibitor

The cyclic AMP-dependent protein kinase inhibitor (PKI) mRNA and protein are negatively and tissue-specifically regulated in the kidney by 1 alpha, 25(OH)2D3. A 17-kb PKI clone, isolated from a chick genomic library, revealed that the PKI gene consists of two exons separated by a 4.5-kb intron. A 411-bp upstream region (constituting 93 bp upstream and 318 bp downstream from the transcriptional start site) containing a putative negative VDRE (nVDRE) fused to the luciferase gene was used for transient transfections of primary cultures of chick kidney cells. Luciferase activity was significantly down-regulated in response to 1 alpha, 25(OH)2D3. This result suggests that the promoter region containing the putative nVDRE plays a pivotal role in the negative regulation of PKI gene transcription.

Prothoracic gland inactivation in Heliothis virescens (F.) (Lepidoptera:Noctuidae) larvae parasitized by Cardiochiles nigriceps Viereck (Hymenoptera:Braconidae)

Heliothis virescens (F.) last instar larvae parasitized by the endophagous braconid Cardiochiles nigriceps Viereck fail to attain the pupal stage, due to a parasitoid-induced alteration of ecdysteroid biosynthesis and metabolism. Currently available information on host prothoracic gland inactivation in this host-parasitoid system is reported here. Prothoracic glands of H. virescens mature larvae show a depressed biosynthetic activity, without undergoing gross morphological disruption. The ultrastructure of gland cells is characterized by minor parasitoid-induced changes, with the rough endoplasmic reticulum appearing more developed and electrondense than in nonparasitized controls. Eventually, the cells of prothoracic glands of parasitized host last instar larvae die but maintain their structural integrity. The inactivation of pupally committed host prothoracic glands is achieved through the disruption of the PTTH signal transduction pathway. The second messenger cAMP appears to be normally produced in response to PTTH stimulation of glands explanted from parasitized host larvae, however the downstream activation of the cAMP-dependent protein kinase does not appear to occur. In fact, a marked underphosphorylation of regulatory target proteins is observed. This underphosphorylation is associated with a significant reduction in general protein synthesis, which appears to be blocked at the translational level, to a redirection of specific protein synthesis and to a drastic suppression of ecdysteroidogenesis. These parameters appeared to be correlated in a kinetic time-course study, confirming their functional link. C. nigriceps polydnavirus (CnPDV) plays a major role in the inactivation of pupally committed host prothoracic glands, while putative factors occurring in the host haemolymph do not seem to be of particular importance at that developmental stage. Southern blot hybridization indicates the occurrence of PKI(protein kinase inhibitor)-like genes in the C. nigriceps genome, which, in contrast, are undetectable in H. virescens.

Tissue-specific expression and regulation by 1,25(OH)2D3 of chick protein kinase inhibitor (PKI) mRNA

The heat-stable protein kinase inhibitor (PKI) protein is a specific and potent competitive inhibitor of the catalytic subunit of cAMP-dependent protein kinase (PKA). Previously, it has been shown that vitamin D status affects chick kidney PKI activity: a 5- to 10-fold increase in PKI activity was observed in kidneys of chronically vitamin D-deficient chicks and treatment with 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) in cultured kidney cells resulted in a 95% decrease in PKI activity. The authors have recently cloned the cDNA for chick kidney PKI and have used the coding sequence to study the regulation of PKI mRNA. Northern analysis showed the expression of two PKI messages, which are 2.7 and 3.3 kb in size. These mRNAs are expressed in brain, muscle, testis, and kidney, but not in pancreas, liver, or intestine. PKI mRNA steady-state levels are downregulated by 47% in kidneys from vitamin D-replete chicks as compared to vitamin D-deficient chicks. PKI mRNA levels in brain, muscle, and testis are not affected by vitamin D status. Treatment of primary chick kidney cultures treated with 10(-7) M 1,25(OH)2D3 for 24h resulted in a 20-30% decrease in PKI mRNA. 1,25(OH)2D3 treatment does not affect the stability of PKI mRNA as determined by treatment of cell cultures with actinomycin D. This study shows that 1,25(OH)2D3 directly and tissue-specifically downregulates PKI mRNA in the chick kidney.