Polyadenylic acid-containing cytoplasmic RNA increases in adenosine 3',5'-cyclic monophosphate-induced 'differentiated' neuroblastoma cells in culture.

Printed in S\\'eden Copyright© 1975 hy Acad(,mic Press. Inc. All riKhts of reproduction in anyfhrm rc.\l'f\'t'd Experimental Cell Research 94 (1975) 88-94 POLY ADENYLIC ACID-CONTAINING CYTOPLASMIC RNA INCREASES IN ADENOSINE 3' ,5'-CYCLIC MONOPHOSPHA TE-INDUCED 'DIFFERENTIATED' NEUROBLASTOMA CELLS IN CULTURE K. N. PRASAD, S. C. BONDY and JANET L. PURDY Departments of Radiology and Neurology, University of Colorado Medical Center, Denver, CO 80220, USA SUMMARY The amount of polyadenylic acid [poly(A)]-containing cytoplasmic RNA in malignant and 'dif- ferentiated' mouse neuroblastoma cells in culture was determined. 4-(3-Butoxy-4-methoxybenzyl)- 2-imidazolidinone (R020-1724), prostaglandin (PG)Ei. serum-free medium, X-irradiation and sodium butyrate were used to induce 'differentiation'. The cAMP-induced 'differentiated' cells had more poly(A)-containing cytoplasmic RNA than the malignant cells; the increase in poly- (A)-RN A was greatest in R020-1724-treated cells. The amount ofpoly(A)-containing cytoplasmic RNA did not significantly change in serum-free medium- or sodium butyrate-treated cells; how- ever, it decreased in cells of confluent phase of growth. The percentage of total radioactive RNA in the cytoplasms of cAMP-induced 'differentiated' cells after l h oflabeling was three-fold greater than that in malignant cells, indicating that transport of RN A from nucleus to cytoplasm occurs at relatively higher rate in 'differentiated' cells. The stability of RNA in cAMP-induced 'dif- ferentiated' cells increased in comparison to malignant cells. The binding of actinomycin D with DNA suggests that the proportion of guanine residues that are accessible to actinomycin D are similar in the nuclei of malignant and cAMP-induced 'differentiated' cells. The present and previous studies suggest that cAMP induces many differentiated functions in neuroblastoma cells by increasing both the transcription and translation of genetic information which is probably masked during malignant transformation of nerve cells. All cell mRNAs except the histone mRNA [1] contain long stretches (100-200 nucleo- tides) of polyadenylic acid [poly(A)], whereas the ribosomal(r)- and transfer(t)- RN As do not [4, 6, 10, 32). The rate of syn- thesis, accumulation and degradation of poly(A)-containing RNA have been meas- ured under a variety of experimental condi- tions in order to obtain insight on the mole- cular mechanisms of growth and differentia- tion in mammalian cells in culture. For ex- ample, the amount and rate of synthesis of cytoplasmic poly(A)-containing RNA do Expt/ Cell Res 94 (1975) not appreciably change with the alteration in growth rate [27]. However, the turnover rate of poly(A)-containing RNA in the non- transformed mouse fibroblasts is propor- tional to the doubling time of cells [11]. The dividing immature muscle cells have high levels of synthesis of poly(A)-containing cytoplasmic RNA; the half-life of poly(A)- containing RNA increases from 10 h in the dividing muscle cells to 50 h in the differ- entiated muscle cells [3]. The poly(A)-con- taining RNA fractions from the liver and the hepatoma polyribosomes are similar