Search

BACKGROUND. Vitamin D has been shown to promote differentiation of cells and inhibit growth in many cancer cells through its effects on nuclear receptors, but it has also been proposed that there may be nonreceptor-mediated effects on cellular function. We investigated the effects of vitamin D on two human colon cancer cell lines obtained from the same patient at early and metastatic stages with and without vitamin D receptor (VDR) and 1-[alpha]-vitamin D hydroxylase activity (1-[alpha]-VD-OHase), respectively. METHODS. Cell lines SW480 (primary colon cancer) and SW620 (metastatic lesion from the same patient) were obtained from the American Type Culture Collection and grown under standard conditions. RNA was extracted by RNeasy Total Isolation Kit (QIAGEN). Reverse-transcription polymerase chain (RT-PCR) reaction was performed by the Superscript Choice System (Gibco BRL). Cells were synchronized by 24-h depletion of fetal bovine serum. Approximately 30,000 cells/well were plated on 6-well Falcon plastic tissue culture dishes. Vitamin D was added to the culture media at concentrations ranging from 10 pmol/L to 10 [micro]mol/L at day of seeding (day 0). Cells were counted by hemocytometer by two observers blinded to treatment every 24 h until a growth curve demonstrated maximal inhibition. The Student's t test was used to assess statistical significance between treated and control groups. RESULTS. RT-PCR results confirmed that the SW480 cell line is [VDR.sub.+] and 1-[alpha]-VD-[OHase.sub.+] whereas the SW620 cell line is [VDR.sub.-] and 1-[alpha]-VD-[OHase.sup.-]. Vitamin D had dose-dependent antiproliferative effects on both cell lines. There was a 67% decrease in growth in the SW480 cell line (P < 0.05) and a 41% decrease in growth in the SW620 cell line (P < 0.05) after 5 d of VD treatment compared with untreated cells. DISCUSSION. These results suggest that the antiproliferative effects mediated by vitamin D may be independent of the VDR because antiproliferation was observed in the cell line lacking the VDR. Alternatively, incubating [VDR.sub.-] cell lines with vitamin D may result in VDR induction. [Supported by National Institutes of Health grant 42710.]

A hysteretic mixed-signal controller for high-frequency switch-mode power supplies that achieves both very fast transient response and constant switching frequency under steady-state operation is presented. The mixed-signal controller combines three control loops: analog nonlinear current loop, digital linear voltage loop, and digital frequency loop. To eliminate the sampling delay associated with conventional digital controllers and improve the transient response performance, the fast nonlinear loop is built with a simple analog hardware. The nonlinear current loop is designed based on the hysteretic control of the output capacitor current. To guarantee the constant switching frequency, under different operating conditions, a digital frequency loop is proposed and implemented. The digital frequency loop eliminates undesirable switching frequency variation, associated with the conventional hysteretic controllers, by digitally adjusting the hysteretic bands around the output voltage reference. The controller operation is experimentally verified with a 5-MHz buck converter. Experimental results demonstrate fast transient response while the constant switching frequency is maintained under steady-state operation. [ABSTRACT FROM AUTHOR]

Expressive loss of the tumor suppressor deleted in colon cancer (DCC) may be superior to lymph node status in predicting patient survival for intermediate stage colon cancer. A polymerase chain reaction (PCR)-based method for detecting DCC would be ideal as a prognostic indicator. DCC is an alternatively spliced molecule; thus, reliability of a PCR test for DCC will depend on amplifying only those regions of the molecule that are lost in the progression of colon cancer. For this reason, we studied a colon cancer cell line model at different stages of tumor progression to determine the alternative splice pattern for DCC. A commercially available colon cancer cell line system at different stages of tumor progression was used to identify which DCC exons are lost by western blot analysis, PCR, and RT-PCR techniques. Colon cancers express abnormal DCC transcripts. The proximal and distal exons are present (exons 2 and 28-29). Exons located in the center of the molecule are absent (6-7 and 18-23). This correlated to DCC protein loss in the cell lines. For clinical utility as a disease marker, exons in the middle portion of the DCC molecule that are spliced out should be utilized. Amplification of the proximal and distal regions will result in falsely concluding that DCC is present when its protein product is not expressed. [ABSTRACT FROM AUTHOR]