Radiation sensitivity of human squamous cell carcinoma cells in vitro is modulated by all-trans and 13-cis-retinoic acid in combination with interferon-alpha.

PURPOSE: Retinoids and interferon-alpha (IFN-alpha) have been shown to exert antiproliferative and radiosensitizing effects. The present study was designed to determine differential effects of retinoids in combination with IFN-alpha on radiation toxicity of 5 human squamous cell carcinoma (SCC) cell lines. METHODS AND MATERIALS: Using clonogenic assays, the effects of all-trans (ATRA), 13-cis-retinoic acid (13cRA), and IFN-alpha on radiation toxicity were analyzed. Basal mRNA expression of the cytoplasmic retinoic acid binding protein, CRABP I, was determined in retinoid-sensitive and -insensitive cell lines by reverse transcriptase/polymerase chain reaction (RT-PCR). RESULTS: Treatment with ATRA, 13cRA, or IFN-alpha resulted in a cell line-specific inhibition of clonogenic survival. A comparison of retinoid-sensitive and insensitive cells revealed that retinoid sensitivity seems to be dependent on the basal expression level of CRABP I. ATRA, 13cRA, and IFN-alpha alone or in combination altered radiation sensitivity by affecting predominantly the alpha-component of the linear-quadratic dose-response curve. Likewise, depending upon the treatment condition the surviving fraction at 2 Gy (SF2) was decreased cell line-specifically. Combined treatment with ATRA or 13cRA and IFN-alpha markedly enhanced radiation cytotoxicity. CONCLUSION: These in vitro data indicate that the combined treatment with retinoids, IFN-alpha, and ionizing radiation could be beneficial for patients presenting with SCC.

A method for isolation of RNA from Pneumocystis carinii.

Total RNA from Pneumocystis carinii obtained directly from the rat lung and from short term culture on A549 cells was evaluated for size and purity. An isolation procedure using guanidine isothiocyanate and lithium chloride was preferable to a hot phenol method. Host cells were eliminated by hypotonic lysis and a series of microfiltrations. Pneumocystis carinii were pretreated with Zymolyase for increased susceptibility to chaotropic agents. The major ribosomal species of P. carinii RNA migrated similarly to Saccharomyces cerevisiae rRNA. The 28s-like species migrated well ahead of rat and A549 cell rRNA and well behind the prokaryotic large rRNA species.

Pneumocystis carinii: sequence from ribosomal RNA implies a close relationship with fungi.

Pneumocystis carinii is the etiologic agent of a lethal pneumonia which occurs in patients with the acquired immune deficiency syndrome (AIDS) and other immunocompromised hosts. The basic biochemical and genetic characteristics of P. carinii are poorly understood and its taxonomic classification as a protozoan is uncertain. To address the taxonomic question, a method was developed for the extraction of total RNA from P. carinii. Denaturing agarose gel electrophoresis showed the two ribosomal RNA species of P. carinii to be similar in size to those of other lower eukaryotes, including Saccharomyces cerevisiae. Three portions of the small ribosomal RNA of P. carinii were sequenced by reverse transcription from oligonucleotide primers. Three hundred seventy-two nucleotides of sequence were obtained. The sequence derived from P. carinii RNA contained regions that previous phylogenetic studies have shown to be highly variable among species, as well as regions that are highly conserved. Comparison of the P. carinii sequence to corresponding sequences of organisms from other taxa showed the P. carinii sequence to be more similar to sequences from the fungi (Saccharomyces cerevisiae, Neurospora crassa, Candida albicans, and Cryptococcus diffuens) than to protozoan sequences. These data suggest that P. carinii is more closely related to fungi than to protozoa.