Changes in the expression of oncogenes encoding nuclear phosphoproteins but not c-Ha-ras have a relationship to monocytic differentiation of HL 60 cells.

Abstract

Abstract. HL 60 cells were subcloned into variants with different sensitivities to the differentiation-inducing effect of 1,25 dihydroxyvitamin D3 (I,25(OH)2D3), as shown by increased oxidative and phagocytic activity and the appearance of cytoplasmic a-naphthyl butyrate esterase. Brief treatment (4 h) with 1,25(OH)2D3 or 5-azacytidine (5-Aza CR) of sensitive sublines induced monocytic differentiation in a fraction of treated cells. The phenotypic differentiation induced by 1,25(OH)2D3 was preceded by altered expression of oncogenes c-myc and c-fos, but not of c-Ha-ras or of the constitutively expressed p72 gene. Treatment with 5-Aza CR had similar effects but in addition increased the rate of transcription of the c-Ha-ras oncogene. In partially resistant sublines exposure to 1,25(OH)2D3 or 5-Aza CR resulted in changes in the levels of c-myc and c-fos mRNA, but the expression of c-Ha-ras gene did not correlate with the phenotypic differentiation. When induction of differentiation in responsive cells was delayed by cycloheximide, a temporal correlation could be made between changes in the expression of the c-myc gene and differentiation. These results suggest that a reduction of the elevated levels of c-myc gene transcription in HL 60 cells is required for the initiation of monocytic differentiation, that the induction of c-fos gene expression is an early step in this process, and that the transient increase in the expression of c-Ha-ras gene by 5-Aza CR is not related to differentiation.

Inhibition of DNA synthesis by an inducer of differentiation of leukemic cells, 1 alpha, 25 dihydroxy vitamin D3, precedes down regulation of the c‐myc gene

“…In contrast, the expression of c-fos became detectable a little later and gradually increased, preceding by a few hr the manifestations of the phenotypic differentiation of these cells (Fig. 31, as reported in more detail in another study (Brelvi and Studzinski, 1986). Specifically, we confirmed the observation of Muller et al (1985) that rapid (< 30 min) induction of c-fos is not detectable following treatment with 1,25(OH)@3.…”

“…Approximately one third of the cells exposed to this regimen show phenotypic differentiation (shown by, e.g., nonspecific esterase, phagocytosis, morphological changes) which peaks 24-36 hr after exposure to the inducer, and the cells then gradually revert to the undifferentiated phenotype. This transient wave of differentiation was shown to be preceded by a reduced rate of cell proliferation and of c-myc gene expression (Studzinski et al, 1985a), and to be accompanied by an increased expression of the c-fos gene (Brelvi and Studzinski, 1986) but these changes were not previously correlated with the altered rates of DNA synthesis, which is the focus of this study.…”

1 alpha,25-dihydroxyvitamin D3 regulates the transcription of carbonic anhydrase II mRNA in avian myelomonocytes.

“…Furthermore, in all these instances and as reported here for CAII mRNA, inhibition of protein synthesis by CHX did not block the effects of 1,25(OH)2D3, indicating that the responses did not necessi-tate the de novo synthesis of other gene products. Instead, we found that it induced an increase in CAII mRNA level, as reported for these other gene products and for differentiationrelated protooncogenes in HL-60 cells (37)(38)(39).…”

Vitamin D Effects on Differentiation and Cell Cycle

“…Indeed, the association between c-Myc downregulation and 1,25(OH) 2 D 3 -induced differentiation of human leukemia cells was one of the earliest findings that initiated the studies of the molecular basis of the cellular changes that follow exposure to this hormone [16,265,309,310]. Subsequently, several studies have shown a marked reduction in c-Myc expression in response to 1,25(OH) 2 D 3 and analog treatment of colon cancer cells [311,312] and prostate cancer cells [268,313], and this was associated with the induction of differentiation [312] and G1 arrest [313].…”