Vitamin D-3 receptor (VDR) expression in HC-11 mammary cells: regulation by growth-modulatory agents, differentiation, and Ha-ras transformation

HC-11 mammary epithelial cells which originate from midpregnant BALB/c mice are able to differentiate in culture after epidermal (EGF) or basic fibrob last (FGF) growth factor pretreatment followed by lactogenic hormone stimul ation (Dexamethasone, Insulin, and Prolactin - DIP). In our study, HC-11 ce lls exhibited specific vitamin D-3 receptors (VDR) determined by Northern a nalysis or flow cytometry and responded to 10 nM vitamin D-3 treatment disp laying strong growth inhibition, arrest in G0/G1 phase without evidence of apoptosis, and VDR mRNA reduction, although the percentage of cells express ing VDR protein remained unchanged. In an attempt to verify if there was a correlation between the growth state of the cells and VDR levels, we have e xamined the effects of growth modulators such as EGF/bFGF and confluency an d transformation by Ha-ras. A down-regulation of VDR expression was observe d after Ha-ras transformation of HC-11 cells which desensitized the cells t o the growth inhibitory effects of vitamin D-3. EGF or bFGF decreased VDR i n parental cells and EGF antagonized the antiproliferative activity of vita min D-3. As well, transition from proliferating to confluent state signific antly reduced VDR levels only in parental cells. DIP-induced HC-11 cell dif ferentiation (monitored by beta-casein transcripts), although leading to ce ll cycle arrest, increased VDR mRNA content, which seems to be rather relat ed to lactogenic hormone induction than to differentiation itself. In fact, DIP-stimulated HC-11 cells in the absence of EGF pretreatment, or DIP-trea ted HC-11ras cultures, also displayed up-regulated VDR level even in the ab sence of differentiation. Concluding, mammary VDR levels might be regulated by growth modulating agents, by physiological conditions of the gland, and by the ras-mediated malignant transformation.