Transcriptional activation of the Cdk inhibitor p21 by vitamin D3 leads to the induced differentiation of the myelomonocytic cell line U937.

Abstract

The hormonal form of vitamin D, 1,25-dihydroxyvitamin D3, acting through its cognate nuclear receptor (vitamin D3 receptor, VDR) will induce myeloid leukemic cell lines to terminally differentiate into monocytes/macrophages. Because VDR acts by transcriptionally regulating responsive genes in a ligand-dependent manner, we sought target genes of the receptor that initiate the differentiation process in response to ligand. We screened a cDNA library prepared from the myelomonocytic U937 cell line with probes generated from either 1,25-dihydroxyvitamin D3-treated or untreated cells. We report here that a candidate clone that hybridized differentially is the Cdk inhibitor p21 war1' cn, l. Furthermore, we show that p21 is transcriptionally induced by 1,25-dihydroxvitamin D 3 in a VDR-dependent, but not p53-dependent, manner, and we identify a functional vitamin D response element in the p21 promoter. Transient overexpression of p21 and/or the related Cdk inhibitor p27 in U937 cells in the absence of 1,25-dihydroxvitamin D3 results in the cell-surface expression of monocyte/macrophage-specific markers, suggesting that ligand-modulated transcriptional induction of the p21 gene facilitates the induced differentiation of this monoblastic cell line. We believe that this is the first report demonstrating that the ectopic overexpression of a Cdk inhibitor such as p21 or p27 directly leads to a terminal differentiation program.

Differential and antagonistic effects of 9-cis-retinoic acid and vitamin D analogues on pancreatic cancer cells in vitro

“…It is therefore likely that regulation by vitamin D analogues of genes whose products are involved in cell differentiation, proliferation and death play the most important role in this resistance. A number of genes are regulated by 1,25D 3 and its analogues, including the cyclin-dependent kinase inhibitors (CDKI) p21 WAF-1 and p27 Kip1 (Liu et al, 1996;Wang et al, 1996;Matsumoto et al, 1998). Both these proteins have been shown to be up-regulated in the pancreatic cancer cell line BxPc-3 after treatment with 1,25D 3 as well as the synthetic analogue 22-oxa-1,25-dihydroxyvitamin D 3 (OCT) (Kawa et al, 1997), implying that this is the mechanism whereby G0/G1 arrest is achieved.…”

Ras induces p21Cip1/Waf1 cyclin kinase inhibitor transcriptionally through Sp1-binding sites

“…Besides p53, transcription factor Ap-2 (Zeng et al, 1997), E2F-1/DP-1 complex (Hiyama et al, 1997), E2A (Prabhu et al, 1997), an ets-oncogene related E1AF (Funaoka et al, 1997), C/EBP , RAR (Liu et al, 1996a), VDR (Liu et al, 1996b), STATs (Chin et al, 1996), and Sp1 family (Biggs et al, 1996;Li et al, 1998;Owen et al, 1998;Prowse et al, 1997;Yan and Zi , 1997) are known to stimulate p21 promoter activity. Our results show that Ras induces p21 transcriptionally and that the Ras-responsive region in p21 promoter spans a short region downstream of the nucleotide 7110 relative to the transcription start site.…”

“…The transactivation is mediated by speci®c p53-binding sites in the p21 promoter (ElDeiry et al, 1993). Other transcriptional activators of p21 include tumor suppressor BRCA-1 , transforming growth factor-b (Datto et al, 1995b), activin A (Zauberman et al, 1997), cytokines acting through STAT-pathway (Chin et al, 1996), nerve growth factor (Yan and Zi , 1997), tumor promoters (Zeng and El-Deiry, 1996), vitamin D 3 (Liu et al, 1996b), retinoic acid receptor (Liu et al, 1996a), glucocorticoids , progesterone (Owen et al, 1998), Raf (Sewing et al, 1997), and MAPKK (Liu et al, 1996c), while Ras-mediated induction of p21 is negatively regulated by Rho (Olson et al, 1998). Furthermore, growth factors PDGF, FGF, and EGF (Michieli et al, 1994), as well as tumor suppressor gene WT1 (Englert et al, 1997) induce p21 mRNA levels.…”

Differential patterns of cell cycle regulatory proteins expression in transgenic models of thyroid tumours

“…Indeed, p21 and/or p27 accumulate in diverse di erentiating normal and tumour cells Franklin and Xiong, 1996;Tron et al, 1996;Durand et al, 1997;Nadal et al, 1997;Tikoo et al, 1997). Their overexpression induces the activation of a di erentiation pathway (Kranenburg et al, 1995;Liu et al, 1996). p27 suppression impairs the di erentiation of mouse keratinocytes and luteal cells Hauser et al, 1997).…”