Association of the type II cAMP-dependent protein kinase with a human thyroid RII-anchoring protein. Cloning and characterization of the RII-binding domain.

The type II cAMP-dependent protein kinase (PKA) is localized to specific subcellular environments through binding of the dimeric regulatory subunit (RII) to anchoring proteins. Subcellular localization is likely to influence which substrates are most accessible to the catalytic subunit upon activation. We have previously shown that the RII-binding domains of four anchoring proteins contain sequences which exhibit a high probability of amphipathic helix formation (Carr, D. W., Stofko-Hahn, R. E., Fraser, I. D. C., Bishop, S. M., Acott, T. E., Brennan, R. G., and Scott J. D. (1991) J. Biol. Chem. 266, 14188-14192). In the present study we describe the cloning of a cDNA which encodes a 1015-amino acid segment of Ht 31. A synthetic peptide (Asp-Leu-Ile-Glu-Glu-Ala-Ala-Ser-Arg-Ile-Val-Asp-Ala-Val-Ile-Glu-Gln-Val -Lys-Ala-Ala-Tyr) representing residues 493-515 encompasses the minimum region of Ht 31 required for RII binding and blocks anchoring protein interaction with RII as detected by band-shift analysis. Structural analysis by circular dichroism suggests that this peptide can adopt an alpha-helical conformation. Both Ht 31 (493-515) peptide and its parent protein bind RII alpha or the type II PKA holoenzyme with high affinity. Equilibrium dialysis was used to calculate dissociation constants of 4.0 and 3.8 nM for Ht 31 peptide interaction with RII alpha and the type II PKA, respectively. A survey of nine different bovine tissues was conducted to identify RII binding proteins. Several bands were detected in each tissues using a 32P-RII overlay method. Addition of 0.4 microM Ht 31 (493-515) peptide to the reaction mixture blocked all RII binding. These data suggest that all anchoring proteins bind RII alpha at the same site as the Ht 31 peptide. The nanomolar affinity constant and the different patterns of RII-anchoring proteins in each tissue suggest that the type II alpha PKA holoenzyme may be specifically targeted to different locations in each type of cell.     

Methylation patterns at the hypervariable X-chromosome locus DXS255 (M27 beta): correlation with X-inactivation status.

Methylation patterns surrounding a hypervariable X-chromosome locus, DXS255, have been analyzed with the restriction enzyme MspI and its methylation-sensitive isoschizomer HpaII. HpaII sites flanking the hypervariable region were found to be methylated on 41 active X chromosomes and unmethylated on 11 inactive X chromosomes present in a range of male, female, and hybrid cells and tissues. This differential methylation pattern coupled with the previously described high level (greater than 90%) of heterozygosity at the DXS255 locus can therefore be applied to determine the inactivation status of X chromosomes in females heterozygous for X-linked disease and in tumor clonality studies.     

Toxic shock syndrome in a patient with systemic lupus erythematosus.

A case is presented of toxic shock syndrome in a patient with systemic lupus erythematosus. Toxic shock syndrome is rarely reported in patients who are immunosuppressed, perhaps because such patients are often treated vigorously with antibiotics at the earliest sign of infection. The association in this case may have been coincidental.     

Comparison of different methods of determining cell viability after exposure to cytotoxic compounds

Cell-survival (of DON and L1210 cells) after treatment with cytotoxic compounds was assessed by measuring cloning efficiency, exclusion of trypan blue and erythrosin B, [⁵¹Cr] release, and attachment of DON cells to glass. Cell survival as measured by cloning efficiency did not correlate with survival measured by any of the other methods. We found that the stainability of cells after drug exposure depended on the cell line used. For example, after 3 h exposure to tubercidin although 100% of both DON and L1210 cells were killed (on basis of cloning efficiency), only 11% of DON cells and 68% of L1210 cells were dead as indicated by staining with erythrosin B. The stainability of cells also depended on the particular drug used. For example, after 24 h exposure of L1210 cells to adriamycin and tubercidin (both killed >99% of cells on basis of cloning efficiency) 21% of cells exposed to adriamycin and 99% of cells exposed to tubercidin were stained. The results obtained with several other cytotoxic compounds are discussed.