Translation of adenovirus 2 late mRNAs microinjected into cultured African green monkey kidney cells.

Adenovirus 2-infected monkey cells fail to synthesize fiber, a 62,000 Mr virion polypeptide expressed at late times in productively infected cells. Yet these cells contain fiber mRNA that, after isolation, can be translated in vitro. The reason for the failure of monkey cells to translate fiber mRNA has been approached by microinjecting adenovirus mRNA into the cytoplasm of cultured monkey cells. Late adenovirus 2 mRNA, isolated from infected HeLa cells, was efficiently expressed when microinjected into the African green monkey kidney cell line CV-C. Expressed viral proteins identified by immunoprecipitation included the adenovirus fiber polypeptide. This result demonstrates that the monkey cell translational apparatus is capable of recognizing and expressing functional adenovirus fiber mRNA. Microinjection of late virus mRNA into cells previously infected with wild-type adenovirus 2 failed to increase significantly the yield of infectious virus.     

Adenovirus proteins associated with mRNA and hnRNA in infected HeLa cells.

The proteins that interact with cytoplasmic and nuclear polyadenylated RNA in adenovirus type 5 (Ad5) infection of HeLa cells were examined by UV-induced RNA-protein cross-linking in intact cells. The Ad5 100-kilodalton late nonvirion protein (100K protein) was cross-linked to both host and viral polyadenylated cytoplasmic RNA (mRNA). The cross-linking of the 100K protein to mRNA appears to correlate with productive infection, because the protein is not cross-linked to mRNA in abortive infection of wild-type Ad5 in monkey cells (CV-1) even though normal amounts of it are produced. However, when CV-1 cells are infected with Ad5 hr404, and Ad5 mutant which overcomes the host restriction to wild-type Ad5 infection in these cells, the 100K protein is cross-linked to mRNA. To identify and obtain antibodies to RNA-contacting proteins, a mouse was immunized with oligo(dT)-selected cross-linked RNA-protein complexes from Ad5-infected cells and the serum was used for immunoblotting experiments. It was found that in addition to the 100K protein, the Ad5 72K DNA-binding protein is also associated with RNA in the infected cells. The 72K DNA-binding protein is cross-linked to polyadenylated nuclear RNA sequences. These findings indicate that adenovirus proteins interact with RNAs in the infected cell and suggest possible mechanisms for the effects of the virus on mRNA metabolism.     

Synthesis of human adenovirus early RNA species is similar in productive and abortive infections of monkey and human cells.

Northern (RNA) blot analysis has been used to show that synthesis of early mRNA species is similar in monkey cells productively or abortively infected with human adenovirus. mRNA species from all five major early regions (1A, 1B, 2, 3, 4) are identical in size and comparable in abundance whether isolated from monkey cells infected with adenovirus type 2 or with the host range mutant Ad2hr400 or coinfected with adenovirus type 2 plus simian virus 40. The mRNA species isolated from monkey cells are identical in size to those isolated from human cells. Production of virus-associated RNA is also identical in productive and abortive infections of monkey cells. Synthesis of virus-associated RNA is, however, significantly greater in HeLa cells than in CV1 cells at late times after infection regardless of which virus is used in the infection.     

Simian virus 40 host range/helper function mutations cause multiple defects in viral late gene expression.

Simian virus 40 (SV40) deletion mutants dlA2459 and dlA2475 express T antigens that lack the normal carboxy terminus. These mutants are called host range/helper function (hr/hf) mutants because they form plaques at 37 degrees C on BSC-1 and Vero monkey kidney cell lines but not on CV-1p monkey kidney cells. Wild-type SV40 can provide a helper function to permit growth of human adenoviruses in monkey kidney cells; the hr/hf mutants cannot. Progeny yields of hr/hf mutants are also cold sensitive in all cell lines tested. Patterns of viral macromolecular synthesis in three cell lines (Vero, BSC-1, and CV-1) at three temperatures (40, 37, and 32 degrees C) were examined to determine the nature of the growth defect of hr/hf mutants. Mutant viral DNA replication was similar to that of the wild type in all three cell lines, indicating that the mutations affect late events in the viral lytic cycle. In mutant-infected Vero cells, in which viral yields were highest, late mRNA levels were similar to those observed during wild-type infection. Levels of viral late mRNA from mutant-infected CV-1 and BSC-1 cells at 32 and 37 degrees C were reduced relative to those of wild-type-infected cells. The steady-state level of the major viral capsid protein, VP1, in mutant-infected CV-1 cells was reduced to the same extent as was late mRNA. The synthesis of agnoprotein could not be detected in mutant-infected CV-1 cells but was readily detected in CV-1 cells infected by wild-type SV40. Primer extension analyses indicated that most late mRNAs from mutant-infected CV-1 cells utilize start sites downstream from the major wild-type cap site (nucleotide 325) and the agnoprotein initiation codon (nucleotide 335). These results indicate that deletion of the carboxyl-terminal domain of T antigen affects viral late mRNA production, both quantitatively and qualitatively. The agnoprotein is detected late in the wild-type SV40 lytic cycle and is thought to play a role in the assembly or maturation of virions. Reduced hr/hf progeny yields could result from decreased capsid protein synthesis and, in the absence of detectable levels of agnoprotein, from inefficient use of available capsid proteins.     

Adenovirus type 5 precursor terminal protein-expressing 293 and HeLa cell lines.

HeLa and 293 cell lines that express biologically active adenovirus type 5 precursor terminal protein (pTP) have been made. The amount of pTP synthesized in these cell lines ranges from barely detectable to greater than that observed in cells infected with the wild-type virus. The pTP-expressing cell lines permit the growth of a temperature-sensitive terminal protein mutant virus sub100r at the nonpermissive temperature. A higher percentage of the stably transfected 293 cell lines expressed terminal protein, and generally at considerably higher levels, than did the HeLa cell lines. While 293 cells appeared to tolerate pTP better than did HeLa cells, high-level pTP expression in 293 cells led to a significantly reduced growth rate. The 293-pTP cell lines produce infectious virus after transfection with purified viral DNA and form plaques when overlaid with Noble agar after infection at low multiplicity. These cell lines offer promise for the production of adenoviruses lacking pTP expression and therefore completely defective for replication.     

Mouse p53 represses the rat brain creatine kinase gene but activates the rat muscle creatine kinase gene.

The creatine kinases (CK) regenerate ATP for cellular reactions with a high energy expenditure. While muscle CK (CKM) is expressed almost exclusively in adult skeletal and cardiac muscle, brain CK (CKB) expression is more widespread and is highest in brain glial cells. CKB expression is also high in human lung tumor cells, many of which contain mutations in p53 alleles. We have recently detected high levels of CKB mRNA in HeLa cells and, in this study, have tested whether this may be due to the extremely low amounts of p53 protein present in HeLa cells. Transient transfection experiments showed that wild-type mouse p53 severely repressed the rat CKB promoter in HeLa but not CV-1 monkey kidney cells, suggesting that, in HeLa but not CV-1 cells, p53 either associates with a required corepressor or undergoes a posttranslational modification necessary for CKB repression. Conversely, mouse wild-type p53 strongly activated the rat CKM promoter in CV-1 cells but not in HeLa cells, suggesting that, in CV-1 cells, p53 may associate with a required coactivator or is modified in a manner necessary for CKM activation. The DNA sequences required for p53-mediated modulations were found to be within bp -195 to +5 of the CKB promoter and within bp -168 to -97 of the CKM promoter. Moreover, a 112-bp fragment from the proximal rat CKM promoter (bp -168 to -57), which contained five degenerate p53-binding elements, was capable of conferring p53-mediated activation on a heterologous promoter in CV-1 cells. Also, this novel p53 sequence, when situated in the native 168-bp rat CKM promoter, conferred p53-mediated activation equal to or greater than that of the originally characterized far-upstream (bp -3160) mouse CKM p53 element. Therefore, CKB and CKM may be among the few cellular genes which could be targets of p53 in vivo. In addition, we analyzed a series of missense mutants with alterations in conserved region II of p53. Mutations affected p53 transrepression and transactivation activities differently, indicating that these activities in p53 are separable. The ability of p53 mutants to transactivate correlated well with their ability to inhibit transformation of rat embryonic fibroblasts by adenovirus E1a and activated Ras.     

Poliovirus mutant that does not selectively inhibit host cell protein synthesis.

A poliovirus type I (Mahoney strain) mutant was obtained by inserting three base pairs into an infectious cDNA clone. The extra amino acid encoded by the insertion was in the amino-terminal (protein 8) portion of the P2 segment of the polyprotein. The mutant virus makes small plaques on HeLa and monkey kidney (CV-1) cells at all temperatures. It lost the ability to mediate the selective inhibition of host cell translation which ordinarily occurs in the first few hours after infection. As an apparent consequence, the mutant synthesizes far less protein than does wild-type virus. In mutant-infected CV-1 cells enough protein was produced to permit a normal course of RNA replication, but the yield of progeny virus was very low. In mutant-infected HeLa cells there was a premature cessation of both cellular and viral protein synthesis followed by a premature halt of viral RNA synthesis. This nonspecific translational inhibition was distinguishable from wild-type-mediated inhibition and did not appear to be part of an interferon or heat shock response. Because the mutant is recessive, our results imply that (at least in HeLa cells) wild-type poliovirus not only actively inhibits translation of cellular mRNAs, but also avoids early inhibition of its own protein synthesis. Cleavage of the cap-binding complex protein P220, which has been associated with the selective inhibition of capped mRNA translation, did not occur in mutant-infected cells. This result supports the hypothesis that cleavage of P220 plays an important role in normal poliovirus-mediated translational inhibition.     

Defective synthesis of early region 4 mRNAs during abortive adenovirus infections in monkey cells.

Human adenovirus 2 grows poorly in monkey cells, partly because of defects in late gene expression. Since deletions in early region 4 (E4) cause similar defects in late gene expression, we examined E4 mRNA expression in abortive infections. Processing of E4 mRNAs was defective during abortive infections, most likely at the level of splicing. At early times in productive infections in HeLa cells, the major E4 species produced is a 2-kb mRNA; at late times, a shift occurs so that smaller spliced E4 mRNAs are also produced. In CV-1 cells, a nonpermissive monkey cell line, this shift did not take place and only the 2-kb species was produced at late times, suggesting a defect in E4 mRNA splicing during abortive infections. The adenovirus DNA-binding protein (DBP) was required for normal processing of E4 mRNAs, since a host range mutant (hr602) containing an altered DBP gene showed a normal late E4 mRNA pattern in CV-1 cells; in addition, DBP was required during infections in HeLa cells for late E4 mRNA expression. DBP was not required for production of the late E4 pattern in transient expression assays in HeLa or 293 cells, suggesting that a second factor in addition to the DBP, present during infection but not transfection, modulates E4 mRNA processing.