To detect transcripts encoding the interleukin-6 receptor (IL-6R) molecule lacking the transmembrane (TM) domain, in various cell lines and peripheral blood mononuclear cells (PBMC), we used the polymerase chain reaction (PCR) with primer pairs that flank the TM domain and which were selected to generate a 398-bp fragment. We detected 398-bp and 304-bp DNA molecules in the PCR products of the U1, J22HL60, MT-2, MT-4, U937 and HL60 cell lines and of PBMC isolated from several individuals. The sequencing analysis of both DNA molecules showed that a 94-bp region consisting of the TM domain of IL-6R was deleted in the 304-bp molecule. Moreover, we detected a soluble (s) IL-6R protein of 45 kDa in culture supernatants of the MT-2, MT-4 and U937 cell lines by radioimmunoprecipitation using specific antibodies against sIL-6R. Our results indicate that active deletion of the TM domain by alternative splicing of mRNA represents one mechanism for release of sIL-6R into the culture supernatants of cells, or into serum or urine.

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Circadian rhythms and zonal variations in the cell proliferation of adult rat adrenal cortex were studied by following the cells in the DNA-synthesizing stage (S-phase) as assessed by 5-bromo-2'-deoxyuridine incorporation into the cell-nuclei and/or by visualizing proliferating cell nuclear antigen. The S-phase cells were observed throughout the day in two regions of the adrenal cortex: (i) a region from the inner half of the zona glomerulosa to near the outer margin of the zona fasciculata, and (ii) the outer one-fourth portion of the zona fasciculata. Very little change in number was observed in the former region between day and night, while a burst of cell proliferation occurred in early morning at 3-4 a.m. in the latter region. A prominent rise in the plasma adrenocorticotropic hormone (ACTH) concentration preceded the burst of cell proliferation by about 4 h. Upon raising the plasma ACTH concentration by administration of ACTH or metyrapone, prominent cell proliferation also occurred in the same portion of the zona fasciculata 4-6 h after the provoked ACTH surge. Thus at least two sites in rat adrenal cortex are responsible for cytogenesis in this endocrine organ, and respond differentially to day/night cycles and circulating ACTH levels.

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