Expression and regulation of alkaline phosphatases in human breast cancer MCF‐7 cells

Abstract

The effect of retinoic acid and dexamethasone on alkaline phosphatase (AP) expression was investigated in human breast cancer MCF-7 cells. Cellular AP activity was induced significantly by retinoic acid or dexamethasone in a time-dependent and dose-dependent fashion. A marked synergistic induction of AP activity was observed when the cells were incubated with both agents simultaneously. Two AP isozymes, tissuenonspecific (TNAP) and intestinal (IAP), were shown to be expressed in MCF-7 cells as confirmed by the differential rate of thermal inactivation of these isozymes and RT-PCR. Based on the two-isozyme thermalinactivation model, the specific activities for TNAP and IAP in each sample were analyzed. TNAP activity was induced only by retinoic acid and IAP activity was induced only by dexamethasone. Whereas dexamethasone conferred no significant effect on TNAP activity, retinoic acid was shown to inhibit IAP activity by < 50%. Interestingly, TNAP was found to be the only isozyme activity superinduced when the cells were costimulated with retinoic acid and dexamethasone. Northern blot and RT-PCR analysis were then used to demonstrate that the steady-state TNAP mRNA level was also superinduced, which indicates that the superinduction is regulated at the transcriptional or post-transcriptional levels. In the presence of the glucocorticoid receptor antagonist RU486, the dexamethasone-mediated induction of IAP activity was blocked completely as expected. However, the ability of RU486 to antagonize the action of glucocorticoid was greatly compromised in dexamethasone-mediated superinduction of TNAP activity. Furthermore, in the presence of retinoic acid, RU486 behaved as an agonist, and conferred superinduction of TNAP gene expression in the same way as dexamethasone. Taken together, these observations suggest that the induction of IAP activity by dexamethasone and the superinduction of TNAP by dexamethasone were mediated through distinct regulatory pathways. In addition, retinoic acid plays an essential role in the superinduction of TNAP gene expression by enabling dexamethasone to exert its agonist activity, which otherwise has no effect.

Activity of phosphatase-sensitive 5-aminolevulinic acid prodrugs in cancer cell lines

“…Although abundantly present in tissues, the regulation of alkaline phosphatase expression changes due to different factors according to cell type. 24,42,43 It has to be noted that PSI-ALA-Hex upon activation gives rise to the production of formaldehyde. Although participating in fundamental biological pathways in cells, the excessive amounts of formaldehyde have toxic effects by inhibiting cell proliferation and leading to apoptosis through the upregulation of tumor suppressor genes p53 and p21 responsible for the cell cycle regulation.…”

The sodium iodide symporter (NIS): Regulation and approaches to targeting for cancer therapeutics

“…Agonists of glucocorticoid receptor (GR), such as dexamethasone (Dex) and hydrocortisone, synergistically increase expression of genes induced by tRA (Medh & Schmidt, 1997; Tsai et al, 2000), including NIS (Dohan et al, 2006; Kogai et al, 2005; Unterholzner et al, 2006). Dex significantly increases iodide uptake (>3-fold with 10 −7 M tRA) in MCF-7 cells both in the presence and absence of tRA (Kogai et al, 2005).…”

Inhibition of growth and increase of alkaline phosphatase activity in cultured human oral cancer cells by all-trans retinoic acid

“…Studies have shown that the antitumour effects of ATRA on colon cancer and osteosarcoma are associated with the activity of ALP 1,10 . Using human breast cancer MCF-7 cells as a model, TSAI et al 26 found that cellular ALP activity was significantly induced by retinoic acid in a time-dependent and dose-dependent fashion. In human head-and-neck tumour cells, the ALP activity is very low 4 .…”