EXPRESSION OF THE HUMAN GROWTH-HORMONE NORMAL GENE (HGH-N) IN PROLIFERATING AND DIFFERENTIATED HL-60 CELLS

The possibility that human leukemic cells could synthesize growth horm one (GH) was investigated in the HL-60 cell line, Western blot analysi s of protein extracts obtained from these cells revealed the existence of a major immunoreactive GH (irGH) band, with an approximate molecul ar weight of 22 kDa, together with lower amounts of 20- and 44-kDa ban ds, Stimulating proliferating HL-60 cells with KCl clearly increased G M concentration in the incubation medium as compared to basal values, RT-P;CR amplification of HL-60 RNA and restriction assay of the amplim ers demonstrated that those proteins were the result of the expression of the GH-N (normal) gene in this cell line, These results were confi rmed by Northern blot, which also showed that the rate of GN-N gene ex pression was clearly dependent upon the proliferative state of the cel ls: while GH transcripts were easily detectable in actively proliferat ing cells, only minute amounts were observed when cells were induced t o differentiate with dimethyl sulphoxide (DMSO), Similar differences w ere observed by Western blot, In all, these findings demonstrate that HL-60 cells are capable to produce and secrete a GH identical to pitui tary GH. Interestingly, the rate of synthesis of the hormone dramatica lly increases when cells are actively proliferating, Therefore, it is likely that locally produced GH might be involved in the control of le ukemic cell. proliferation, Further studies are now in course to estab lish whether this mechanism occurs via an autocrine and/or paracrine w ay. (C) 1996 Academic Press, Inc.