Disease relevance of Prkar1a

• Prkar1a(+/-) mice developed nonpigmented schwannomas and fibro-osseous bone lesions beginning at approximately 6 months of age [1].
• To assess the activity of Tse-1 in other tissues, we transferred mouse chromosome 11 from several different cell types into rat hepatoma recipients [2].
• Effects of RIalpha overexpression on cisplatin sensitivity in human ovarian carcinoma cells [3].
• Intraperitoneal administration of this antisense RIalpha poly-DNP-RNA to SCID mice with transplanted MDA-MB-231 cells was found to inhibit the growth of the xenografts in a concentration-dependent way, prevent metastasis, and drastically reduce mortality [4].
• Prostaglandin E2 (PGE2) stimulated in vitro invasion, migration, and adherence to reconstituted basement membrane by metastatic Lewis lung carcinoma (LLC) clones, but this stimulation was blocked by protein kinase A (PKA) inhibitors and by expression of a transfected mutant RI alpha which blocks PKA activation [5].
• Although prolactinomas were observed in KO and control mice, the KO mice exhibited a significantly increased frequency of pituitary tumors compared with wild-type or conventional Prkar1a(+/-) mice [6].

High impact information on Prkar1a

• Surprisingly, a subset of these alf-responsive genes is negatively controlled by the tissue-specific extinguisher locus Tse-1 [7].
• We also provide evidence that human Tse-1 resides on the homologous chromosome (human chromosome 17), and that hybrids retaining active Tse-1 loci lack TAT-specific mRNA [8].
• In mice there are four R genes (encoding RI alpha, RI beta, RII alpha, and RII beta) and two C gene (encoding C alpha and C beta), expressed in tissue-specific patterns [9].
• Expression of the RI alpha subunit of cAMP-dependent protein kinase type I is enhanced in human cancer cell lines, in primary tumours, in cells after transformation and in cells upon stimulation of growth [10].
• We have investigated the effect of sequence-specific inhibition of RI alpha gene expression on in vivo tumour growth [10].

Chemical compound and disease context of Prkar1a

• In the present study, we have investigated the sequence- and target-specific effects of exogenous RIalpha antisense oligodeoxynucleotides (ODNs) and endogenous antisense gene on tumor growth, apoptosis, and cAMP signaling in androgen-insensitive prostate cancer cells, both in vitro and in nude mice [11].
• Based on histamine release from IgE-sensitized and nonsensitized basophil leukocytes of healthy donors, we detected anti-Fc epsilon RI alpha autoantibodies in sera from 38 (23%) urticaria patients and evidence for anti-IgE antibodies in a further nine patients [12].

Biological context of Prkar1a

• These were associated with allelic losses of the mouse chromosome 11 Prkar1a locus, an increase in total type II PKA activity, and higher RIIbeta protein levels [13].
• Down-regulation of Prkar1a by up to 70% was achieved in transgenic mouse tissues and embryonic fibroblasts, with concomitant changes in kinase activity and increased cell proliferation, respectively [13].
• Genetic analysis indicated that allelic loss occurred in a subset of tumor cells, suggesting that complete loss of Prkar1a plays a key role in tumorigenesis [1].
• To bypass the early embryonic lethality of Prkar1a(-/-) mice, we established transgenic mice carrying an antisense transgene for Prkar1a exon 2 (X2AS) under the control of a tetracycline-responsive promoter [13].
• RI alpha transcripts have accumulated in the muscle by day 12 of mouse embryogenesis, and localization is established by day 14, at about the time of formation of junctions [14].

Anatomical context of Prkar1a

• Similarly, tissue-specific ablation of Prkar1a from a subset of facial neural crest cells caused the formation of schwannomas with divergent differentiation [1].
• RI alpha transcripts are distributed in muscle fibers exactly as acetylcholinesterase, showing that this RNA is localized at the neuromuscular junction [14].
• When FSC1 was used as the bait to screen a mouse testis cDNA library, two clones were isolated encoding the type Ialpha regulatory subunit (RIalpha) of cAMP-dependent protein kinase [15].
• This defect in the production and migration of mesoderm can be completely rescued by crossing RIalpha mutants to mice carrying a targeted disruption in the Calpha catalytic subunit, demonstrating that unregulated PKA activity rather than a specific loss of RIalpha is responsible for the phenotype [16].
• These in vivo findings are consistent with observations made in cell culture, where we demonstrate that the overexpression of Calpha in NIH 3T3 cells results in increased RIalpha protein without increases in the rate of RIalpha synthesis or the level of RIalpha mRNA [17].

Associations of Prkar1a with chemical compounds

• This mouse provides a novel, useful tool for the investigation of cyclic AMP, RIalpha, and PKA functions and confirms the critical role of Prkar1a in tumorigenesis in endocrine and other tissues [13].
• Holoenzymes containing RI beta Ala and RI beta Ala/Ile gave Ka values which were higher than wild type RI beta, with the double mutant shifting toward the Ka value of RI alpha holoenzymes by about 30% [18].
• The 18-mer antisense DNA against the RIalpha subunit of PKA was conjugated via a primary amine on the 5'-end with the NHS esters of HYNIC and MAG3 and by the cyclic anhydride of DTPA [19].
• Retroviral-infected A2780 cells overexpressing wild-type RI alpha cDNA displayed a four- to eightfold greater sensitivity to cisplatin compared with parental cells [3].
• The nucleotide sequence indicated that the transforming activity was created by the fusion of the ret tyrosine kinase domain with part of the RI alpha regulatory subunit of protein kinase A (PKA) [20].

Regulatory relationships of Prkar1a

• The capacity of PKA to regulate the cytoskeletal organization of tumor cells was further studied with the use of LLC variants that had been stably transfected to over-express the C alpha subunit of PKA (CEV cells) or to express a mutant cAMP-resistant PKA RI alpha subunit resulting in a defective PKA (REV cells) [21].
• In addition to having catalytic activity, the C alpha subunit from Kin- cells is inhibited in the presence of mouse RI alpha regulatory subunit, indicating that formation of the holoenzyme complex is normal [22].
• These results suggest a novel mechanism of cAMP signaling through the interaction of RIalpha with CoxVb thereby regulating cytochrome c oxidase activity as well as the cytochrome c levels [23].

Other interactions of Prkar1a

• In addition, RI alpha recruits C alpha protein to the junction, providing at this site the potential for local responsiveness to cAMP [14].
• This assignment demonstrated that the Tat-1 structural gene was not syntenic with Tse-1, a chromosome 11-linked locus that negatively regulates TAT expression in trans (A. M. Killary and R. E. K. Fournier, Cell 38:523-534, 1984) [24].
• This is apparently the first report of an RIalpha-specific protein kinase A anchoring protein tethering domain [15].
• Brachyury mRNA expression in the primitive streak of RIalpha mutants is significantly reduced, consistent with later deficits in axial, paraxial, and lateral plate mesodermal derivatives [16].
• We have created null mutations in the RIbeta and RIIbeta regulatory subunit genes in mice, and find that both result in an increase in the level of RIalpha protein in tissues that normally express the beta isoforms [17].

Analytical, diagnostic and therapeutic context of Prkar1a

• This was supported by the finding that site-directed mutagenesis to disrupt the amphipathic helix eliminated RIalpha binding [15].
• Primary embryonic fibroblasts from RIalpha mutant embryos display an abnormal cytoskeleton and an altered ability to migrate in cell culture [16].
• Northern blot analysis of PKA subunit mRNAs following treatment of each cell line with 8-Cl-adenosine demonstrated decreased C alpha mRNA expression, increased RII alpha mRNA, and no change in RI alpha mRNA abundance [25].
• Antitumor activity and pharmacokinetics of a mixed-backbone antisense oligonucleotide targeted to the RIalpha subunit of protein kinase A after oral administration [26].
• This study further provides a basis for clinical studies of the antisense oligonucleotide targeted to the RIalpha subunit of PKA (GEM 231) as a cancer therapeutic agent used alone or in combination with conventional chemotherapy [26].

References