Induction of IFN-alphabeta enables Listeria monocytogenes to suppress macrophage activation by IFN-gamma.

Production of type I interferon (IFN; IFN-alphabeta) increases host susceptibility to Listeria monocytogenes, whereas type II IFN (IFN-gamma) activates macrophages to resist infection. We show that these opposing immunological effects of IFN-alphabeta and IFN-gamma occur because of cross talk between the respective signaling pathways. We found that cultured macrophages infected with L. monocytogenes were refractory to IFN-gamma treatment as a result of down-regulation of the IFN-gamma receptor (IFNGR). The soluble factor responsible for these effects was identified as host IFN-alphabeta. Accordingly, macrophages and dendritic cells (DCs) showed reduced IFNGR1 expression and reduced responsiveness to IFN-gamma during systemic infection of IFN-alphabeta-responsive mice. Furthermore, the increased resistance of mice lacking the IFN-alphabeta receptor (IFNAR(-/-)) to L. monocytogenes correlated with increased expression of IFN-gamma-dependent activation markers by macrophages and DCs and was reversed by depletion of IFN-gamma. Thus, IFN-alphabeta produced in response to bacterial infection and other stimuli antagonizes the host response to IFN-gamma by down-regulating the IFNGR. Such cross talk permits prioritization of IFN-alphabeta-type immune responses and may contribute to the beneficial effects of IFN-beta in treatment of inflammatory diseases such as multiple sclerosis.

A posttranscriptional role for the yeast Paf1-RNA polymerase II complex is revealed by identification of primary targets.

The yeast Paf1 complex (Paf1C: Paf1, Cdc73, Ctr9, Rtf1, and Leo1) is associated with RNA Polymerase II (Pol II) at promoters and coding regions of transcriptionally active genes, but transcript abundance for only a small subset of genes is altered by loss of Paf1. By using conditional and null alleles of PAF1 and microarrays, we determined the identity of both primary and secondary targets of the Paf1C. Neither primary nor secondary Paf1C target promoters were responsive to loss of Paf1. Instead, Paf1 loss altered poly(A) site utilization of primary target genes SDA1 and MAK21, resulting in increased abundance of 3'-extended mRNAs. The 3'-extended MAK21 RNA is sensitive to nonsense-mediated decay (NMD), as revealed by its increased abundance in the absence of Upf1. Therefore, although the Paf1C is associated with Pol II at initiation and during elongation, these critical Paf1-dependent changes in transcript abundance are due to alterations in posttranscriptional processing.

Separation of the Saccharomyces cerevisiae Paf1 complex from RNA polymerase II results in changes in its subnuclear localization.

The yeast Paf1 complex (Paf1C), composed of Paf1, Ctr9, Cdc73, Rtf1, and Leo1, associates with RNA polymerase II (Pol II) at promoters and in the actively transcribed portions of mRNA genes. Loss of Paf1 results in severe phenotypes and significantly reduced levels of the other Paf1C components. In contrast, loss of Rtf1 causes relatively subtle phenotypic changes and no reduction in the other Paf1C factors but disrupts the association of these factors with Pol II and chromatin. To elucidate the fate of the Paf1C when dissociated from Pol II, we examined the localization of the Paf1C components in paf1 and rtf1 mutant yeast strains. We found that although the Paf1C factors remain nuclear in paf1 and rtf1 strains, loss of Paf1 or Rtf1 results in a change in the subnuclear distribution of the remaining factors. In wild-type cells, Paf1C components are present in the nucleoplasm but not the nucleolus. In contrast, in both paf1 and rtf1 strains, the remaining factors are found in the nucleolus as well as the nucleoplasm. Loss of Paf1 affects nucleolar function; we observed that expression of MAK21 and RRP12, important for rRNA processing, is reduced concomitant with an increase in rRNA precursors in a paf1 strain. However, these changes are not the result of relocalization of the Paf1C because loss of Rtf1 does not cause similar changes in rRNA processing. Instead, we speculate that the change in localization may reflect a link between the Paf1C and newly synthesized mRNAs as they exit the nucleus.

The CUSP DeltaNp63alpha isoform of human p63 is downregulated by solar-simulated ultraviolet radiation.

BACKGROUND: In normal human keratinocytes, a p53-like protein, DeltaNp63alpha, also known as CUSP, is constitutively and abundantly expressed. The significant constitutive expression of DeltaNp63alpha in stratified epithelium has been proposed to maintain the proliferative capacity of basal cells, blocking the consequences of inappropriate p53 activation. OBJECTIVE: To determine the response of keratinocyte DeltaNp63alpha to ultraviolet radiation (UVR), a stimulus for p53 activation. METHODS: Cultured normal human keratinocytes were exposed to graded doses of solar-simulated UVR. The expression of DeltaNp63alpha protein and mRNA were measured with Western and Northern blotting. Normal mouse skin was exposed to UVR, and DeltaNp63alpha expression assessed with immunohistochemistry. RESULTS: Increasing doses of UVR virtually shut off DeltaNp63alpha protein and mRNA expression in cultured normal human keratinocytes and in normal mouse skin in vivo. CONCLUSION: This study supports the hypothesis that in situations where p53 activation is desirable, as with DNA-damaging UVR, DeltaNp63alpha downregulation occurs and may possibly allow for better target gene transcription by p53.

CUSP/p63 expression in basal cell carcinoma.

Chronic ulcerative stomatitis protein (CUSP), the most abundant cutaneous isoform of p63, is a p53-related gene essential for epithelial development. CUSP lacks the N-terminal transactivation domain found on other p53 family members and has been shown to inhibit p53 function in vitro. In this study, biopsies of normal skin (21 of 21), benign neoplasms [seborrheic keratosis (3 of 3), acrochordon (2 of 3), and verruca plana (3 of 3)], and squamous cell carcinomas (SCC) (4 of 4) displayed strong nuclear CUSP immuno-reactivity in epidermal cells. In contrast few basal cell carcinomas (BCC) (7 of 27) and sebaceous nevi (1 of 2) displayed this pattern of CUSP immunoreactivity. Thus, biopsies of cutaneous conditions characterized by sonic hedgehog (SHH) pathway dysregulation were more than 86 times as likely to lack CUSP/p63 immunofluorescence as were other cutaneous samples. Adjacent normal-appearing skin from patients with basal cell nevus syndrome (BCNS) (2 of 3) also lacked CUSP immuno-staining. Lastly, a BCC arising in a patched heterozygous mouse also lacked CUSP immuno-staining. Because CUSP mRNA and protein were detected via Northern and Western analysis in BCC samples lacking CUSP immuno-staining, we sequenced the coding region of CUSP from two non-staining BCCs but found no mutations. Therefore, CUSP appears to be present, unmutated, and yet frequently undetectable by immunofluorescence in cutaneous lesions in both humans and mice that are associated with SHH pathway dysregulation (BCCs, BCNS, and nevus sebaceous).