Effect of UV light on small nuclear RNA synthesis: increased inhibition during postirradiation cell incubation.

Abstract

It has been shown previously that the synthesis of small nuclear RNAs (snRNAs) Ul, U2, U3, U4, and U5, in contrast to that of all other RNA species tested, decreases markedly within 2 h of cell incubation after exposure to UV light (254 nm), while pyrimidine dimers are being removed from DNA. We examined the possibility that the postirradiation cell incubation-dependent, UV light-induced inhibition of snRNA synthesis might reflect hypersensitivity of the snRNA transcriptional domains to single-stranded DNA nicks or relaxation of DNA torsional stress or both that occur during DNA repair. This late suppression of snRNA biosynthesis was as pronounced in UV light-irradiated (DNA incision-deficient) xeroderma pigmentosum fibroblasts (complementation group A) as in irradiated normal human fibroblasts. The synthesis of snRNAs was not preferentially sensitive to -y radiation (which produces single-stranded DNA breaks) or novobiocin or nalidixic acid (which induce DNA relaxation). Neither of these two drugs prevented the UV light-induced inhibition of snRNA synthesis observed during postirradiation cell incubation. These results suggest that the late suppression of snRNA synthesis does not result from hypersensitivity of snRNA transcriptional domains to single-stranded DNA cleavages or relaxation of DNA torsional strain. The UV light-induced late inhibition of snRNA synthesis: (i) shows an inactivation curve whose slope differs from that observed immediately after irradiation; (ii) is seen in untransformed cells as well as established cells lines; and (iii) has been conserved between birds and mammals.The size of transcription units can be measured by UV transcription mapping (24). UV light induces the random dimerization of adjacent pyrimidine pairs along a DNA strand, interrupting the elongation of transcription. There are three unexpected features about the effect of UV radiation on the biosynthesis of small nuclear RNA (snRNA) species Ul, U2, U3, U4, and U5. First, although Ul through U5 snRNAs and their known precursors are very short (1, 5), their biosynthesis is very sensitive to UV light (3, 6). In contrast, for all other RNA species tested there is a strict correlation between the length of the transcription unit and the UV light sensitivity of its expression (24). The term early inhibition will be used here for the UV light-induced suppression of snRNA biosynthesis that is easily seen after relatively high UV doses and very short postirradiation cell incubations (for example, about 290 J/m2 and no more than 10 min, respectively). Second, a small fraction of Ul, U2, U3, and U5 snRNA biosynthesis remains unaffected at high UV doses when cell radiolabeling begins soon (within 10 min) after irradiation (6). The presence of a UV lightresistant subpopulation of RNA synthesis has not been observed in any other RNA species whose synthesis is inhibited by UV radiation. Third, the suppression of Ul through U5 snRNA synthesis increases within 2 h of postirradiation cell incubation (6). This has not been seen in any other ...

Transcriptional regulation of human small nuclear RNA genes

“…One initial hint of such an activity arose from studies demonstrating that the transcription of numerous snRNA genes by both RNA polymerase II and III is sharply down regulated in response to UV light treatment for an extended period beyond the time required for repair of lesions that might impair transcription [123][124][125][126][127][128]. This initial finding suggested that a factor activated in response to DNA damage was capable of restricting snRNA gene transcription or alternatively that an essential factor was lost after DNA damage.…”

Epigallocatechin gallate induced apoptosis in Sarcoma180 cells in vivo: Mediated by p53 pathway and inhibition in U1B, U4-U6 UsnRNAs expression

“…The differential metabolism of the U1-U6 UsnRNAs during the cellular proliferation, differentiation, development, and lung carcinogenesis has been reported [26][27][28][29][30][31]. The association of U5 in in vitro transformation [60] and reduced expression of UsnRNAs due to UV exposure have also been seen [61][62][63]. This indicates that, the alterations in the expression of U1B and U4-U6 UsnRNAs during EGCG induced apoptosis in S180 cells in vivo might have some effect on this phenomenon.…”

Effect of ultraviolet light on the expression of genes for human U1 RNA

“…1A). 5s RNA transcription was monitored as a control, since it is not affected appreciably in whole cells at the W doses tested (Eliceiri, 1979;Eliceiri and Smith, 1983;Morra et al, 1986a). The U 1 gene fragment used, generated a -1.2-kb runoff transcript (ten times longer than 5 s RNA).…”

“…Second, snRNAs Ul-U5 are the only RNA species whose syntheses exhibit a delayed inhibition induced by UV light. It requires about 1-2 h r of cell incubation after irradiation and UV doses that are about tenfold lower than those needed to get comparable effects immediately after irradiation (the synthesis of messenger RNA, the major RNA polymerase 11 product, is not affected) (Eliceiri and Smith, 1983; Morra et al, 1986a). Several observations suggest that the immediate and delayed inhibitions of U1 RNA synthesis induced by UV radiation are separate reactions and that U1 RNA transcription is the step affected in both (Eliceiri and Smith, 1983; Morra et al, 1986a,b).…”